# Source code for gui.viewport

    #
    ##
    ##  This file is part of pyFormex 1.0.5  (Sat Feb 16 10:40:32 CET 2019)
    ##  pyFormex is a tool for generating, manipulating and transforming 3D
    ##  geometrical models by sequences of mathematical operations.
    ##  Home page: http://pyformex.org
    ##  Project page:  http://savannah.nongnu.org/projects/pyformex/
    ##  Copyright 2004-2018 (C) Benedict Verhegghe (benedict.verhegghe@ugent.be)
    ##  Distributed under the GNU General Public License version 3 or later.
    ##
    ##  This program is free software: you can redistribute it and/or modify
    ##  it under the terms of the GNU General Public License as published by
    ##  the Free Software Foundation, either version 3 of the License, or
    ##  (at your option) any later version.
    ##
    ##  This program is distributed in the hope that it will be useful,
    ##  but WITHOUT ANY WARRANTY; without even the implied warranty of
    ##  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ##  GNU General Public License for more details.
    ##
    ##  You should have received a copy of the GNU General Public License
    ##  along with this program.  If not, see http://www.gnu.org/licenses/.
    ##
    """Interactive OpenGL Canvas embedded in a Qt4 widget.

    This module implements user interaction with the OpenGL canvas defined in
    module :mod:`canvas`.
    `QtCanvas` is a single interactive OpenGL canvas, while `MultiCanvas`
    implements a dynamic array of multiple canvases.
    """
    from __future__ import absolute_import, division, print_function

    import math
    import numpy as np
    from OpenGL import GL
    #
    # TODO: this should be removed !
    from numpy import *

    import pyformex as pf
    from pyformex import zip, round, utils

    from pyformex.opengl import canvas
    from pyformex.gui import (
        QtCore, QtGui, QtOpenGL, QtWidgets,
        image, toolbar,
        )

    from pyformex.collection import Collection
    from pyformex.coords import Coords
    from pyformex.arraytools import isInt,unitVector
    from pyformex.gui.signals import *

    # Some 2D vector operations
    # We could do this with the general functions of coords.py,
    # but that would be overkill for this simple 2D vectors

    def dotpr (v, w):
        """Return the dot product of vectors v and w"""
        return v[0]*w[0] + v[1]*w[1]

    def length (v):
        """Return the length of the vector v"""
        return math.sqrt(dotpr(v, v))

    def projection(v, w):
        """Return the (signed) length of the projection of vector v on vector w."""
        return dotpr(v, w)/length(w)

    # signals

    # keys
    ESC = QtCore.Qt.Key_Escape
    RETURN = QtCore.Qt.Key_Return    # Normal Enter
    ENTER = QtCore.Qt.Key_Enter      # Num Keypad Enter

    # mouse actions
    PRESS = 0
    MOVE = 1
    RELEASE = 2

    # mouse buttons
    LEFT = QtCore.Qt.LeftButton
    MIDDLE = QtCore.Qt.MidButton
    RIGHT = QtCore.Qt.RightButton
    _buttons = [LEFT, MIDDLE, RIGHT]

    # modifiers
    NONE = QtCore.Qt.NoModifier
    SHIFT = QtCore.Qt.ShiftModifier
    CTRL = QtCore.Qt.ControlModifier
    ALT = QtCore.Qt.AltModifier
    META = QtCore.Qt.MetaModifier
    ALLMODS = SHIFT | CTRL | ALT | META
    _modifiers = [NONE, SHIFT, CTRL, ALT, META]
    _modifiername = ['NONE', 'SHIFT', 'CTRL', 'ALT', 'META']

    def modifierFlag(mod):
        try:
            return _modifiers[_modifiername.index(mod)]
        except:
            return NONE

    def modifierName(mod):
        try:
            return _modifiername[_modifiers.index(mod)]
        except:
            return 'UNKNOWN'

    # mouse modifiers used during picking actions
    _PICK_MOVE = [ modifierFlag(i) for i in pf.cfg['gui/mouse_mod_move'] ]
    _PICK_SET = modifierFlag(pf.cfg['gui/mouse_mod_set'])
    _PICK_ADD = modifierFlag(pf.cfg['gui/mouse_mod_add'])
    _PICK_REMOVE = modifierFlag(pf.cfg['gui/mouse_mod_remove'])

    ############### OpenGL Format #################################

    opengl_format = None

    def setOpenGLFormat():
        """Set the correct OpenGL format.

        On a correctly installed system, the default should do well.
        The default OpenGL format can be changed by command line options::

           --dri   : use the Direct Rendering Infrastructure, if available
           --nodri : do not use the DRI
           --opengl : set the opengl version
        """
        global opengl_format
        pf.debug("Get OpenGL Format", pf.DEBUG.OPENGL)
        fmt = QtOpenGL.QGLFormat.defaultFormat()
        if pf.options.debuglevel & pf.DEBUG.OPENGL:
            pf.debug("Got OpenGL Format", pf.DEBUG.OPENGL)
            pf.debug(OpenGLFormat(fmt), pf.DEBUG.OPENGL)
        if pf.options.dri is not None:
            fmt.setDirectRendering(pf.options.dri)
        if pf.options.opengl:
            try:
                major, minor = [int(o) for o in pf.options.opengl.split('.')]
                fmt.setVersion(major, minor)
            except:
                pass

        if pf.options.debuglevel & pf.DEBUG.OPENGL:
            pf.debug("Set OpenGL Format", pf.DEBUG.OPENGL)
            pf.debug(OpenGLFormat(fmt), pf.DEBUG.OPENGL)
        QtOpenGL.QGLFormat.setDefaultFormat(fmt)
        #QtOpenGL.QGLFormat.setOverlayFormat(fmt)
        #fmt.setDirectRendering(False)
        opengl_format = fmt
        if pf.options.debuglevel & pf.DEBUG.OPENGL:
            pf.debug(OpenGLFormat(fmt), pf.DEBUG.OPENGL)
        return fmt

    def getOpenGLContext():
        ctxt = QtOpenGL.QGLContext.currentContext()
        if ctxt is not None:
            printOpenGLContext(ctxt)
        return ctxt

    def OpenGLSupportedVersions(flags):
        """Return the supported OpenGL version.

        flags is the return value of QGLFormat.OpenGLVersionFlag()

        Returns a list with tuple (k,v) where k is a string describing an Opengl
        version and v is True or False.
        """
        flag = QtOpenGL.QGLFormat.OpenGLVersionFlag
        keys = [ k for k in dir(flag) if k.startswith('OpenGL') and not k.endswith('None')]
        return [ (k, bool(int(flags) & int(getattr(flag, k)))) for k in keys ]

    def OpenGLFormat(fmt=None):
        """Some information about the OpenGL format."""
        if fmt is None:
            fmt = opengl_format
        flags = fmt.openGLVersionFlags()
        s = [ "OpenGL: %s" % fmt.hasOpenGL(),
            "OpenGl Version: %s.%s (%x)" % (fmt.majorVersion(), fmt.minorVersion(), int(flags)),
            "OpenGLOverlays: %s" % fmt.hasOpenGLOverlays(),
            "Double Buffer: %s" % fmt.doubleBuffer(),
            "Depth Buffer: %s" % fmt.depth(),
            "RGBA: %s" % fmt.rgba(),
            "Alpha Channel: %s" % fmt.alpha(),
            "Accumulation Buffer: %s" % fmt.accum(),
            "Stencil Buffer: %s" % fmt.stencil(),
            "Stereo: %s" % fmt.stereo(),
            "Direct Rendering: %s" % fmt.directRendering(),
            "Overlay: %s" % fmt.hasOverlay(),
            "Plane: %s" % fmt.plane(),
            "Multisample Buffers: %s" % fmt.sampleBuffers(),
            ''
            ]
        s.append("\nSupported OpenGL versions:")
        for k, v in OpenGLSupportedVersions(flags):
            s.append("  %s: %s" % (k, v))
        return '\n'.join(s)

    def printOpenGLContext(ctxt):
        if ctxt:
            print("context is valid: %d" % ctxt.isValid())
            print("context is sharing: %d" % ctxt.isSharing())
        else:
            print("No OpenGL context yet!")

    ### Some (OLD) drawing functions ############################################

    def drawDot(x, y):
        """Draw a dot at canvas coordinates (x,y)."""
        GL.glBegin(GL.GL_POINTS)
        GL.glVertex2f(x, y)
        GL.glEnd()

    def drawLine(x1, y1, x2, y2):
        """Draw a straight line from (x1,y1) to (x2,y2) in canvas coordinates."""
        GL.glBegin(GL.GL_LINES)
        GL.glVertex2f(x1, y1)
        GL.glVertex2f(x2, y2)
        GL.glEnd()

    def drawGrid(x1, y1, x2, y2, nx, ny):
        """Draw a rectangular grid of lines

        The rectangle has (x1,y1) and and (x2,y2) as opposite corners.
        There are (nx,ny) subdivisions along the (x,y)-axis. So the grid
        has (nx+1) * (ny+1) lines. nx=ny=1 draws a rectangle.
        nx=0 draws 1 vertical line (at x1). nx=-1 draws no vertical lines.
        ny=0 draws 1 horizontal line (at y1). ny=-1 draws no horizontal lines.
        """
        GL.glBegin(GL.GL_LINES)
        ix = range(nx+1)
        if nx==0:
            jx = [1]
            nx = 1
        else:
            jx = ix[::-1]
        for i, j in zip(ix, jx):
            x = (i*x2+j*x1)/nx
            GL.glVertex2f(x, y1)
            GL.glVertex2f(x, y2)

        iy = range(ny+1)
        if ny==0:
            jy = [1]
            ny = 1
        else:
            jy = iy[::-1]
        for i, j in zip(iy, jy):
            y = (i*y2+j*y1)/ny
            GL.glVertex2f(x1, y)
            GL.glVertex2f(x2, y)
        GL.glEnd()

    def drawRect(x1, y1, x2, y2):
        """Draw the circumference of a rectangle."""
        drawGrid(x1, y1, x2, y2, 1, 1)

    ################# Canvas Mouse Event Handler #########################

    class CursorShapeHandler(object):
        """A class for handling the mouse cursor shape on the Canvas.

        """
        cursor_shape = { 'default': QtCore.Qt.ArrowCursor,
                         'pick': QtCore.Qt.CrossCursor,
                         'busy': QtCore.Qt.BusyCursor,
                         }

        def __init__(self, widget):
            """Create a CursorHandler for the specified widget."""
            self.widget = widget

        def setCursorShape(self, shape):
            """Set the cursor shape to shape"""
            if shape not in QtCanvas.cursor_shape:
                shape = 'default'
            self.setCursor(QtCanvas.cursor_shape[shape])

        def setCursorShapeFromFunc(self, func):
            """Set the cursor shape to shape"""
            if func in [ self.mouse_rectangle, self.mouse_pick ]:
                shape = 'pick'
            else:
                shape = 'default'
            self.setCursorShape(shape)

    class CanvasMouseHandler(object):
        """A class for handling the mouse events on the Canvas.

        """
        def setMouse(self,button,func,mod=NONE):
            pf.debug(button, mod, pf.DEBUG.MOUSE)
            self.mousefncsaved[mod][button].append(self.mousefnc[mod][button])
            self.mousefnc[mod][button] = func
            self.setCursorShapeFromFunc(func)
            pf.debug("MOUSE %s" % func, pf.DEBUG.MOUSE)
            pf.debug("MOUSE SAVED %s" % self.mousefncsaved[mod][button], pf.DEBUG.MOUSE)

        def resetMouse(self,button,mod=NONE):
            pf.debug("MOUSE SAVED %s" % self.mousefncsaved[mod][button], pf.DEBUG.MOUSE)
            try:
                func = self.mousefncsaved[mod][button].pop()
            except:
                pf.debug("AAAAAHHH, COULD NOT POP", pf.DEBUG.MOUSE)
                func = None
            self.mousefnc[mod][button] = func
            self.setCursorShapeFromFunc(func)
            pf.debug("RESETMOUSE %s" % func, pf.DEBUG.MOUSE)
            pf.debug("MOUSE SAVED %s" % self.mousefncsaved[mod][button], pf.DEBUG.MOUSE)

        def getMouseFunc(self):
            """Return the mouse function bound to self.button and self.mod"""
            return self.mousefnc.get(int(self.mod), {}).get(self.button, None)

    ################# Single Interactive OpenGL Canvas ###############

    class QtCanvas(QtOpenGL.QGLWidget, canvas.Canvas):
        """A canvas for OpenGL rendering.

        This class provides interactive functionality for the OpenGL canvas
        provided by the :class:`canvas.Canvas` class.

        Interactivity is highly dependent on Qt4. Putting the interactive
        functions in a separate class makes it esier to use the Canvas class
        in non-interactive situations or combining it with other GUI toolsets.

        The QtCanvas constructor may have positional and keyword arguments. The
        positional arguments are passed to the QtOpenGL.QGLWidget constructor,
        while the keyword arguments are passed to the canvas.Canvas constructor.
        """
        cursor_shape = { 'default': QtCore.Qt.ArrowCursor,
                         'pick': QtCore.Qt.CrossCursor,
                         'draw': QtCore.Qt.CrossCursor,
                         'busy': QtCore.Qt.BusyCursor,
                         }

        selection_filters = [ 'none', 'single', 'closest', 'connected', 'closest-connected' ]

        # private signal class
        class Communicate(QtCore.QObject):
            CANCEL = Signal()
            DONE   = Signal()

        def __init__(self,*args,**kargs):
            """Initialize an empty canvas."""
            QtOpenGL.QGLWidget.__init__(self,*args)
            if pf.options.debuglevel & pf.DEBUG.OPENGL:
                pf.debug("QtCanvas.__init__:\n"+OpenGLFormat(self.format()),pf.DEBUG.OPENGL)
            # Define our privatee signals
            self.signals = self.Communicate()
            self.CANCEL = self.signals.CANCEL
            self.DONE   = self.signals.DONE
            #
            self.setMinimumSize(32, 32)
            self.setSizePolicy(QtWidgets.QSizePolicy.MinimumExpanding, QtWidgets.QSizePolicy.MinimumExpanding)
            self.setFocusPolicy(QtCore.Qt.StrongFocus)
            canvas.Canvas.__init__(self,**kargs)
            self.setCursorShape('default')
            self.button = None
            self.mod = NONE
            self.dynamouse = True  # dynamic mouse action works on mouse move
            self.dynamic = None    # what action on mouse move
            self.mousefnc = {}
            self.mousefncsaved = {}
            for mod in _modifiers:
                self.mousefnc[mod] = {}
                self.mousefncsaved[mod] = {}
                for button in _buttons:
                    self.mousefnc[mod][button] = None
                    self.mousefncsaved[mod][button] = []
            # Initial mouse funcs are dynamic handling
            # Also some modifier keys are bound to mouse movement operations
            # These can be used during picking operations

            for mod in set(_PICK_MOVE):
                self.setMouse(LEFT, self.dynarot, mod)
                self.setMouse(MIDDLE, self.dynapan, mod)
                self.setMouse(RIGHT, self.dynazoom, mod)
            self.pick_mode = None
            self.pick_mode_subsel = 'any'
            self.selection = Collection()
            self.trackfunc = None
            self.pick_func = {
                'actor': self.pick_actors,
                'element': self.pick_elements,
                'face': self.pick_faces,
                'edge': self.pick_edges,
                'point': self.pick_points,
                'number': self.pick_numbers,
                }
            self.picked = None
            self.closest_pick = None
            self.pickable = None
            self.drawmode = None
            self.drawing_mode = None
            self.drawing = None
            # Drawing options
            self.resetOptions()

        def getSize(self):
            """Return the size of this canvas"""
            from pyformex.gui.guimain import Size
            return Size(self)

        def saneSize(self, width=0, height=0):
            """Return a cleverly resized canvas size.

            Parameters:

            - `width`: int: requested width in pixels. Set automatically if <= 0.
            - `height`: int: requested height in pixels. Set automatically if <= 0.

            Returns a tuple of positive integers (width,height).

            If both specified values are positive, returns the values unchanged.
            If only one of the values is positive, returns that value unchanged,
            while the other one is determined automatically from the aspect ratio
            of the current canvas.
            If both values are <=0, returns the current canvas size.
            """
            if width<=0 or height <= 0:
                wc,hc = self.getSize()
                if height > 0:
                    width = round(float(height)/hc*wc)
                elif width > 0:
                    height = round(float(width)/wc*hc)
                else:
                    width,height = wc,hc
            return width, height

        # TODO: negative sizes should probably resize all viewports
        # OR we need to implement frames
        def changeSize(self, width, height):
            """Resize the canvas to (width x height).

            If a negative value is given for either width or height,
            the corresponding size is set equal to the maximum visible size
            (the size of the central widget of the main window).

            Note that this may not have the expected result when multiple
            viewports are used.
            """
            if width < 0 or height < 0:
                w, h = pf.GUI.maxCanvasSize()
                if width < 0:
                    width = w
                if height < 0:
                    height = h
            self.resize(width, height)

        def image(self,w=None,h=None,remove_alpha=True):
            """Return the current OpenGL rendering in an image format.

            Parameters:

            - `w`, `h`: requested size (in pixels) of the image. The default
              is to use the current canvas size. If only one is specified,
              the aspect ratio of the current canvas is kept.
            - `remove_alpha`: bool. If True (default), the alpha channel is
              removed from the image.

            Returns the current OpenGL rendering as a QImage of the specified
            size.
            """
            if remove_alpha:
                from pyformex.plugins.imagearray import removeAlpha
                return removeAlpha(self.image(w,h,False))

            self.makeCurrent()
            wc,hc = pf.canvas.getSize()
            w,h = self.saneSize(w,h)
            vcanvas = QtOpenGL.QGLFramebufferObject(w,h)
            vcanvas.bind()
            self.resize(w,h)
            self.display()
            GL.glFlush()
            qim = vcanvas.toImage()
            vcanvas.release()
            self.resize(wc,hc)
            GL.glFlush()
            del vcanvas
            return qim

        def rgb(self,w=None,h=None,remove_alpha=True):
            """Return the current OpenGL rendering in an array format.

            Parameters:

            - `w`, `h`: requested size (in pixels) of the image. The default
              is to use the current canvas size. If only one is specified,
              the aspect ratio of the current canvas is kept.
            - `remove_alpha`: bool. If True (default), the alpha channel is
              removed from the image.

            Returns the current OpenGL rendering as a numpy array of
            type uint and shape (w,h,3) if remove_alpha is True (default)
            or shape (w,h,4) if remove_alpha is False.
            """
            from pyformex.plugins.imagearray import qimage2numpy
            qim = self.image(w,h,False)
            ar, cm = qimage2numpy(qim)
            if remove_alpha:
                ar = ar [...,:3]
            return ar

        def outline(self, size=(0,0), profile='luminance', level=0.5, bgcolor=None, nproc=None):
            """Return the outline of the current rendering

            Parameters:

            - `size`: a tuple of ints (w,h) specifying the size of the image to
              be used in outline detection. A non-positive value will be set
              automatically from the current canvas size or aspect ratio.
            - `profile`: the function used to translate pixel colors into a single
              value. The default is to use the luminance of the pixel color.
            - `level`: isolevel at which to construct the outline.
            - `bgcolor`: a color that is to be interpreted as background color
              and will get a pixel value -0.5.
            - `nproc`: number of processors to be used in the image processing.
              Default is to use as many as available.

            Returns the outline as a Formex of plexitude 2.

            Note:

            - 'luminance' is currently the only profile implemented.
            - `bgcolor` is currently experimental.
            """
            from pyformex.plugins.isosurface import isoline
            from pyformex.formex import Formex
            from pyformex.opengl.colors import luminance, RGBcolor
            self.camera.lock()
            w,h = self.saneSize(*size)
            data = self.rgb(w,h)
            shape = data.shape[:2]

            if bgcolor:
                bgcolor = RGBcolor(bgcolor)
                print("bgcolor = %s" % (bgcolor,))
                bg = (data==bgcolor).all(axis=-1)
                print(bg)
                data = luminance(data.reshape(-1,3)).reshape(shape) + 0.5
                data[bg] = -0.5

            else:
                data = luminance(data.reshape(-1,3)).reshape(shape)

            #print(data[:2,:2])
            rng = data.max() - data.min()
            bbox = self.bbox
            ctr = self.camera.project((bbox[0]+bbox[1])*.05)
            axis = unitVector(self.camera.eye-self.camera.focus)
            #
            # NOTE: the + [0.5,0.5] should be checked and then be
            #       moved inside the isoline function!
            #
            seg = isoline(data,data.min()+level*rng,nproc=nproc) + [0.5,0.5]
            if size is not None:
                wc,hc = pf.canvas.getSize()
                sx = float(wc)/w
                sy = float(hc)/h
                #print("Post scaling %s,%s" % (sx,sy))
                seg[...,0] *= sx
                seg[...,1] *= sy
            X = Coords(seg).trl([0.,0.,ctr[0][2]])
            shape = X.shape
            X = self.camera.unproject(X.reshape(-1,3)).reshape(shape)
            self.camera.unlock()
            F = Formex(X)
            F.attrib(axis=axis)
            return F

        def getPickModes(self):
            return [mode for mode in self.pick_func]

        def setCursorShape(self, shape):
            """Set the cursor shape to shape"""
            if shape not in QtCanvas.cursor_shape:
                shape = 'default'
            #self.setCursor(QtGui.QCursor(QtCanvas.cursor_shape[shape]))
            self.setCursor(QtCanvas.cursor_shape[shape])

        def setCursorShapeFromFunc(self, func):
            """Set the cursor shape to shape"""
            if func in [ self.mouse_rectangle, self.mouse_pick ]:
                shape = 'pick'
            elif func == self.mouse_draw:
                shape = 'draw'
            else:
                shape = 'default'
            self.setCursorShape(shape)

        def setMouse(self,button,func,mod=NONE):
            pf.debug("setMouse %s %s %s" % (button, mod, func), pf.DEBUG.MOUSE)
            self.mousefncsaved[mod][button].append(self.mousefnc[mod][button])
            self.mousefnc[mod][button] = func
            if button == LEFT and mod == NONE:
                self.setCursorShapeFromFunc(func)
            #print self.mousefnc

        def resetMouse(self,button,mod=NONE):
            pf.debug("resetMouse %s %s" % (button, mod), pf.DEBUG.MOUSE)
            try:
                func = self.mousefncsaved[mod][button].pop()
            except:
                func = None
            self.mousefnc[mod][button] = func
            if button == LEFT and mod == NONE:
                self.setCursorShapeFromFunc(func)
            #print self.mousefnc

        def getMouseFunc(self):
            """Return the mouse function bound to self.button and self.mod"""
            return self.mousefnc.get(int(self.mod), {}).get(self.button, None)

        def zoom_rectangle(self):
            self.start_rectangle(func=self.zoomRectangle)

        def get_rectangle(self,):
            self.start_rectangle(func=None)
            self.selection_timer = QtCore.QThread
            while not self.rectangle:
                self.selection_timer.msleep(20)
                pf.app.processEvents()
            return self.rectangle

        def start_rectangle(self,func=None):
            self.rectangle = None
            self.rectangle_func = func
            self.setMouse(LEFT, self.mouse_rectangle)

        def finish_rectangle(self):
            self.resetMouse(LEFT)
            try:
                self.rectangle_func(*self.rectangle)
            except:
                pass
            self.update()
            self.selection_timer = None

        def mouse_rectangle(self, x, y, action):
            """Process mouse events during interactive rectangle zooming.

            On PRESS, record the mouse position.
            On MOVE, create a rectangular zoom window.
            On RELEASE, zoom to the picked rectangle.
            """
            if action == PRESS:
                self.makeCurrent()
                self.update()
                if self.trackfunc:
                    #print "PRESS",self.trackfunc,pf.canvas.camera.focus
                    pf.canvas.camera.setTracking(True)
                    x, y, z = pf.canvas.camera.focus
                    self.zplane = pf.canvas.project(x, y, z, True)[2]
                    #print 'ZPLANE',self.zplane
                    self.trackfunc(x, y, self.zplane)
                self.begin_2D_drawing()
                GL.glEnable(GL.GL_COLOR_LOGIC_OP)
                # An alternative is GL_XOR #
                GL.glLogicOp(GL.GL_INVERT)
                # Draw rectangle
                self.draw_state_rect(x, y)
                self.swapBuffers()

            elif action == MOVE:
                if self.trackfunc:
                    #print "MOVE",self.trackfunc
                    #print 'ZPLANE',self.zplane
                    self.trackfunc(x, y, self.zplane)
                # Remove old rectangle
                self.swapBuffers()
                self.draw_state_rect(*self.state)
                # Draw new rectangle
                self.draw_state_rect(x, y)
                self.swapBuffers()

            elif action == RELEASE:
                GL.glDisable(GL.GL_COLOR_LOGIC_OP)
                self.end_2D_drawing()
                x0 = min(self.statex, x)
                y0 = min(self.statey, y)
                x1 = max(self.statex, x)
                y1 = max(self.statey, y)
                self.rectangle = x0,y0,x1,y1
                self.finish_rectangle()

    ####################### INTERACTIVE PICKING ############################

        def start_selection(self, mode, filter, pickable=None):
            """Start an interactive picking mode.

            If selection mode was already started, mode is disregarded and
            this can be used to change the filter method.
            """
            pf.debug("START SELECTION", pf.DEBUG.GUI)
            pf.debug("Mode is %s" % self.pick_mode, pf.DEBUG.GUI)
            if self.pick_mode is None:
                self.setMouse(LEFT, self.mouse_pick)
                self.setMouse(LEFT, self.mouse_pick, SHIFT)
                self.setMouse(LEFT, self.mouse_pick, CTRL)
                self.setMouse(RIGHT, self.emit_done)
                self.setMouse(RIGHT, self.emit_cancel, SHIFT)
                self.DONE.connect(self.accept_selection)
                self.CANCEL.connect(self.cancel_selection)
                self.pick_mode = mode
                self.pickable = pickable
                self.selection_front = None

            if filter == 'none':
                filter = None
            self.selection_filter = filter
            if filter is None:
                self.selection_front = None
            self.selection.clear()
            self.selection.setType(self.pick_mode)
            pf.debug("START SELECTION DONE", pf.DEBUG.GUI)

        def wait_selection(self):
            """Wait for the user to interactively make a selection."""
            pf.debug("WAIT SELECTION", pf.DEBUG.GUI)
            self.selection_timer = QtCore.QThread
            self.selection_busy = True
            while self.selection_busy:
                self.selection_timer.msleep(20)
                pf.app.processEvents()
            pf.debug("WAIT SELECTION DONE", pf.DEBUG.GUI)

        def finish_selection(self):
            """End an interactive picking mode."""
            pf.debug("FINISH SELECTION", pf.DEBUG.GUI)
            self.resetMouse(LEFT)
            self.resetMouse(LEFT, SHIFT)
            self.resetMouse(LEFT, CTRL)
            self.resetMouse(RIGHT)
            self.resetMouse(RIGHT, SHIFT)
            self.DONE.disconnect(self.accept_selection)
            self.CANCEL.disconnect(self.cancel_selection)
            self.pick_mode = None
            self.pickable = None
            pf.debug("FINISH SELECTION DONE", pf.DEBUG.GUI)

        def accept_selection(self,clear=False):
            """Accept or cancel an interactive picking mode.

            If clear == True, the current selection is cleared.
            """
            self.selection_accepted = True
            if clear:
                self.selection.clear()
                self.selection_accepted = False
            self.selection_canceled = True
            self.selection_busy = False

        def cancel_selection(self):
            """Cancel an interactive picking mode and clear the selection."""
            self.accept_selection(clear=True)

        def pick(self,mode='actor',oneshot=False,func=None,filter=None,pickable=None):
            """Interactively pick objects from the viewport.

            - `mode`: defines what to pick : one of
              ``['actor','element','point','number','edge']``
            - `oneshot`: if True, the function returns as soon as the user ends
              a picking operation. The default is to let the user
              modify his selection and only to return after an explicit
              cancel (ESC or right mouse button).
            - `func`: if specified, this function will be called after each
              atomic pick operation. The Collection with the currently selected
              objects is passed as an argument. This can e.g. be used to highlight
              the selected objects during picking.
            - `filter`: defines what elements to retain from the selection: one of
              ``[None,'single','closest,'connected']``.

              - None (default) will return the complete selection.
              - 'closest' will only keep the element closest to the user.
              - 'connected' will only keep elements connected to

                - the closest element (set picked)
                - what is already in the selection (add picked).

                Currently this only works when picking mode is 'element' and
                for Actors having a partitionByConnection method.

            Returns a (possibly empty) Collection with the picked items.
            After return, the value of the pf.canvas.selection_accepted variable
            can be tested to find how the picking operation was exited:
            True means accepted (right mouse click, ENTER key, or OK button),
            False means canceled (ESC key, or Cancel button). In the latter case,
            the returned Collection is always empty.

            """
            self.setFocus()
            self.selection_canceled = False
            self.start_selection(mode, filter, pickable)
            while not self.selection_canceled:
                self.wait_selection()
                if not self.selection_canceled:
                    # selection by mouse_picking
                    self.pick_func[self.pick_mode]()
                    if len(self.picked) > 0:
                        if self.selection_filter is None:
                            if self.mod == _PICK_SET:
                                self.selection.set(self.picked)
                            elif self.mod == _PICK_ADD:
                                self.selection.add(self.picked)
                            elif self.mod == _PICK_REMOVE:
                                self.selection.remove(self.picked)
                        elif self.selection_filter == 'single':
                            if self.mod == _PICK_SET:
                                self.selection.set([self.closest_pick[0]])
                            elif self.mod == _PICK_ADD:
                                self.selection.add([self.closest_pick[0]])
                            elif self.mod == _PICK_REMOVE:
                                self.selection.remove([self.closest_pick[0]])
                        elif self.selection_filter == 'closest':
                            if self.selection_front is None or \
                                   self.mod == _PICK_SET or \
                                   (self.mod == _PICK_ADD and self.closest_pick[1] < self.selection_front[1]):
                                self.selection_front = self.closest_pick
                                self.selection.set([self.closest_pick[0]])
                        elif self.selection_filter == 'connected':
                            if self.selection_front is None or \
                                   self.mod == _PICK_SET or \
                                   len(self.selection) == 0:
                                self.selection_front = self.closest_pick
                                closest_actor, closest_elem = [int(i) for i in self.selection_front[0]]
                            elif self.mod == _PICK_ADD:
                                closest_elem = self.selection.get(closest_actor)[0]
                            if self.mod == _PICK_SET:
                                self.selection.set(self.picked)
                            elif self.mod == _PICK_ADD:
                                self.selection.add(self.picked)
                            elif self.mod == _PICK_REMOVE:
                                self.selection.remove(self.picked)
                            if self.mod == _PICK_SET or \
                                   self.mod == _PICK_ADD:
                                conn_elems = self.actors[closest_actor].object.connectedElements(closest_elem, self.selection.get(closest_actor))
                                self.selection.set(conn_elems, closest_actor)
                    elif self.mod == _PICK_SET:
                        # Nothing picked and set mode:
                        self.selection.set([])
                    if func:
                        func(self, self.selection)
                    self.update()
                    if oneshot:
                        self.accept_selection()
            if func and not self.selection_accepted:
                func(self, self.selection)
            self.finish_selection()
            return self.selection

        def pickNumbers(self,*args,**kargs):
            """Go into number picking mode and return the selection."""
            return self.pick('numbers',*args,**kargs)

    #################### Interactive drawing ####################################

        def idraw(self,mode='point',npoints=-1,zplane=0.,func=None,coords=None,preview=False):
            """Interactively draw on the canvas.

            This function allows the user to interactively create points in 3D
            space and collects the subsequent points in a Coords object. The
            interpretation of these points is left to the caller.

            - `mode`: one of the drawing modes, specifying the kind of objects you
              want to draw. This is passed to the specified `func`.
            - `npoints`: If -1, the user can create any number of points. When >=0,
              the function will return when the total number of points in the
              collection reaches the specified value.
            - `zplane`: the depth of the z-plane on which the 2D drawing is done.
            - `func`: a function that is called after each atomic drawing
              operation. It is typically used to draw a preview using the current
              set of points. The function is passed the current Coords and the
              `mode` as arguments.
            - `coords`: an initial set of coordinates to which the newly created
              points should be added. If specified, `npoints` also counts these
              initial points.
            - `preview`: **Experimental** If True, the preview funcion will also
              be called during mouse movement with a pressed button, allowing to
              preview the result before a point is created.

            The drawing operation is finished when the number of requested points
            has been reached, or when the user clicks the right mouse button or
            hits 'ENTER'.
            The return value is a (n,3) shaped Coords array.
            To know in which way the drawing was finished check
            pf.canvas.draw_accepted: True means mouse right click / ENTER,
            False means ESC button on keyboard.
            """
            self.setFocus()
            self.draw_canceled = False
            self.start_draw(mode, zplane, coords)
            try:
                if preview:
                    self.previewfunc = func
                else:
                    self.previewfunc = None

                while not self.draw_canceled:
                    self.wait_selection()
                    if not self.draw_canceled:
                        self.drawn = Coords(self.drawn).reshape(-1, 3)
                        self.drawing = Coords.concatenate([self.drawing, self.drawn])
                        if func:
                            func(self.drawing, self.drawmode)
                    if npoints > 0 and len(self.drawing) >= npoints:
                        self.accept_draw()
                if func and not self.draw_accepted:
                    func(self.drawing, self.drawmode)
            finally:
                self.finish_draw()
            return self.drawing

        def start_draw(self, mode, zplane, coords):
            """Start an interactive drawing mode."""
            self.setMouse(LEFT, self.mouse_draw)
            self.setMouse(RIGHT, self.emit_done)
            self.setMouse(RIGHT, self.emit_cancel, SHIFT)
            self.DONE.connect(self.accept_draw)
            self.CANCEL.connect(self.cancel_draw)
            self.drawmode = mode
            self.zplane = float(zplane)
            self.drawing = Coords(coords)

        def finish_draw(self):
            """End an interactive drawing mode."""
            self.resetMouse(LEFT)
            self.resetMouse(RIGHT)
            self.resetMouse(RIGHT, SHIFT)
            self.DONE.disconnect(self.accept_draw)
            self.CANCEL.disconnect(self.cancel_draw)
            self.drawmode = None

        def accept_draw(self,clear=False):
            """Cancel an interactive drawing mode.

            If clear == True, the current drawing is cleared.
            """
            self.draw_accepted = True
            if clear:
                self.drawing = Coords()
                self.draw_accepted = False
            self.draw_canceled = True
            self.selection_busy = False

        def cancel_draw(self):
            """Cancel an interactive drawing mode and clear the drawing."""
            self.accept_draw(clear=True)

        def mouse_draw(self, x, y, action):
            """Process mouse events during interactive drawing.

            On PRESS, do nothing.
            On MOVE, do nothing.
            On RELEASE, add the point to the point list.
            """
            if action == PRESS:
                self.makeCurrent()
                self.update()
                if self.trackfunc:
                    print("ENABLE TRACKING")
                    pf.canvas.camera.setTracking(True)

            elif action == MOVE:
                if pf.app.hasPendingEvents():
                    return
                if self.trackfunc:
                    self.trackfunc(x, y, self.zplane)
                    #pf.app.processEvents()
                if self.previewfunc:
                    self.swapBuffers()
                    self.drawn = self.unproject(x, y, self.zplane)
                    self.drawn = Coords(self.drawn).reshape(-1, 3)
                    self.previewfunc(Coords.concatenate([self.drawing, self.drawn]), self.drawmode)
                    self.swapBuffers()

            elif action == RELEASE:
                self.drawn = self.unproject(x, y, self.zplane)
                self.drawn = Coords(self.drawn).reshape(-1, 3)
                self.selection_busy = False

    ##########################################################################
     # line drawing mode #

        def drawLinesInter(self,mode='line',oneshot=False,func=None):
            """Interactively draw lines on the canvas.

            - oneshot: if True, the function returns as soon as the user ends
              a drawing operation. The default is to let the user
              draw multiple lines and only to return after an explicit
              cancel (ESC or right mouse button).
            - func: if specified, this function will be called after each
              atomic drawing operation. The current drawing is passed as
              an argument. This can e.g. be used to show the drawing.

            When the drawing operation is finished, the drawing is returned.
            The return value is a (n,2,2) shaped array.
            """
            self.setFocus()
            self.drawing_canceled = False
            self.start_drawing(mode)
            while not self.drawing_canceled:
                self.wait_drawing()
                if not self.drawing_canceled:
                    if self.edit_mode: # an edit mode from the edit combo was clicked
                        if self.edit_mode == 'undo' and self.drawing.size != 0:
                            self.drawing = delete(self.drawing, -1, 0)
                        elif self.edit_mode == 'clear':
                            self.drawing = empty((0, 2, 2), dtype=int)
                        elif self.edit_mode == 'close' and self.drawing.size != 0:
                            line = asarray([self.drawing[-1, -1], self.drawing[0, 0]])
                            self.drawing = append(self.drawing, line.reshape(-1, 2, 2), 0)
                        self.edit_mode = None
                    else: # a line was drawn interactively
                        self.drawing = append(self.drawing, self.drawn.reshape(-1, 2, 2), 0)
                    if func:
                        func(self.drawing)
                if oneshot:
                    self.accept_drawing()
            if func and not self.drawing_accepted:
                func(self.drawing)
            self.finish_drawing()
            return self.drawing

        def start_drawing(self, mode):
            """Start an interactive line drawing mode."""
            pf.debug("START DRAWING MODE", pf.DEBUG.GUI)
            self.setMouse(LEFT, self.mouse_draw_line)
            self.setMouse(RIGHT, self.emit_done)
            self.setMouse(RIGHT, self.emit_cancel, SHIFT)
            self.DONE.connect(self.accept_drawing)
            self.CANCEL.connect(self.cancel_drawing)
            #self.setCursorShape('pick')
            self.drawing_mode = mode
            self.edit_mode = None
            self.drawing = empty((0, 2, 2), dtype=int)

        def wait_drawing(self):
            """Wait for the user to interactively draw a line."""
            self.drawing_timer = QtCore.QThread
            self.drawing_busy = True
            while self.drawing_busy:
                self.drawing_timer.msleep(20)
                pf.app.processEvents()

        def finish_drawing(self):
            """End an interactive drawing mode."""
            pf.debug("END DRAWING MODE", pf.DEBUG.GUI)
            #self.setCursorShape('default')
            self.resetMouse(LEFT)
            self.resetMouse(RIGHT)
            self.resetMouse(RIGHT, SHIFT)
            self.DONE.disconnect(self.accept_drawing)
            self.CANCEL.disconnect(self.cancel_drawing)
            self.drawing_mode = None

        def accept_drawing(self,clear=False):
            """Cancel an interactive drawing mode.

            If clear == True, the current drawing is cleared.
            """
            pf.debug("CANCEL DRAWING MODE", pf.DEBUG.GUI)
            self.drawing_accepted = True
            if clear:
                self.drawing = empty((0, 2, 2), dtype=int)
                self.drawing_accepted = False
            self.drawing_canceled = True
            self.drawing_busy = False

        def cancel_drawing(self):
            """Cancel an interactive drawing mode and clear the drawing."""
            self.accept_drawing(clear=True)

        def edit_drawing(self, mode):
            """Edit an interactive drawing."""
            self.edit_mode = mode
            self.drawing_busy = False

    ######## QtOpenGL interface ##############################

        def initializeGL(self):
            # if pf.options.debuglevel & pf.DEBUG.GUI:
            #     p = self.sizePolicy()
            #     print("Size policy %s,%s,%s,%s" % (p.horizontalPolicy(), p.verticalPolicy(), p.horizontalStretch(), p.verticalStretch()))
            self.glinit()
            self.initCamera()
            self.resizeGL(self.width(), self.height())
            self.setCamera()

        def	resizeGL(self, w, h):
            self.setSize(w, h)

        def	paintGL(self):
            if not self.mode2D:
                self.display()

    ####### MOUSE EVENT HANDLERS ############################

        # Mouse functions can be bound to any of the mouse buttons
        # LEFT, MIDDLE or RIGHT.
        # Each mouse function should accept three possible actions:
        # PRESS, MOVE, RELEASE.
        # On a mouse button PRESS, the mouse screen position and the pressed
        # button are always saved in self.statex,self.statey,self.button.
        # The mouse function does not need to save these and can directly use
        # their values.
        # On a mouse button RELEASE, self.button is cleared, to avoid further
        # move actions.
        # Functions that change the camera settings should call saveModelView()
        # when they are done.
        # ATTENTION! The y argument is positive upwards, as in normal OpenGL
        # operations!

        def dynarot(self, x, y, action):
            """Perform dynamic rotation operation.

            This function processes mouse button events controlling a dynamic
            rotation operation. The action is one of PRESS, MOVE or RELEASE.
            """
            if action == PRESS:
                w, h = self.getSize()
                self.state = [self.statex-w/2, self.statey-h/2 ]

            elif action == MOVE:
                w, h = self.getSize()
                # set all three rotations from mouse movement
                # tangential movement sets twist,
                # but only if initial vector is big enough
                x0 = self.state        # initial vector
                d = length(x0)
                if d > h/8:
                    x1 = [x-w/2, y-h/2]     # new vector
                    a0 = math.atan2(x0[0], x0[1])
                    a1 = math.atan2(x1[0], x1[1])
                    an = (a1-a0) / math.pi * 180
                    ds = utils.stuur(d, [-h/4, h/8, h/4], [-1, 0, 1], 2)
                    twist = - an*ds
                    self.camera.rotate(twist, 0., 0., 1.)
                    self.state = x1
                # radial movement rotates around vector in lens plane
                x0 = [self.statex-w/2, self.statey-h/2]    # initial vector
                if x0 == [0., 0.]:
                    x0 = [1., 0.]
                dx = [x-self.statex, y-self.statey]        # movement
                b = projection(dx, x0)
                if abs(b) > 5:
                    val = utils.stuur(b, [-2*h, 0, 2*h], [-180, 0, +180], 1)
                    rot =  [ abs(val), -dx[1], dx[0], 0 ]
                    self.camera.rotate(*rot)
                    self.statex, self.statey = (x, y)
                self.update()

            elif action == RELEASE:
                self.update()
                self.camera.saveModelView()

        def dynapan(self, x, y, action):
            """Perform dynamic pan operation.

            This function processes mouse button events controlling a dynamic
            pan operation. The action is one of PRESS, MOVE or RELEASE.
            """
            if action == PRESS:
                pass

            elif action == MOVE:
                w, h = self.getSize()
                dx, dy = float(self.statex-x)/w, float(self.statey-y)/h
                self.camera.transArea(dx, dy)
                self.statex, self.statey = (x, y)
                self.update()

            elif action == RELEASE:
                self.update()
                self.camera.saveModelView()

        def dynazoom(self, x, y, action):
            """Perform dynamic zoom operation.

            This function processes mouse button events controlling a dynamic
            zoom operation. The action is one of PRESS, MOVE or RELEASE.
            """
            if action == PRESS:
                self.state = [self.camera.dist, self.camera.area.tolist(), pf.cfg['gui/dynazoom']]

            elif action == MOVE:
                w, h = self.getSize()
                dx, dy = float(self.statex-x)/w, float(self.statey-y)/h
                for method, state, value, size in zip(self.state[2], [self.statex, self.statey], [x, y], [w, h]):
                    if method == 'area':
                        d = float(state-value)/size
                        f = exp(4*d)
                        self.camera.zoomArea(f, area=asarray(self.state[1]).reshape(2, 2))
                    elif method == 'dolly':
                        d = utils.stuur(value, [0, state, size], [5, 1, 0.2], 1.2)
                        self.camera.dist = d*self.state[0]

                self.update()

            elif action == RELEASE:
                self.update()
                self.camera.saveModelView()

        def wheel_zoom(self, delta):
            """Zoom by rotating a wheel over an angle delta"""
            f = 2**(delta/120.*pf.cfg['gui/wheelzoomfactor'])
            if pf.cfg['gui/wheelzoom'] == 'area':
                self.camera.zoomArea(f)
            elif pf.cfg['gui/wheelzoom'] == 'lens':
                self.camera.zoom(f)
            else:
                self.camera.dolly(f)
            self.update()

        def emit_done(self, x, y, action):
            """Emit a DONE event by clicking the mouse.

            This is equivalent to pressing the ENTER button."""
            if action == RELEASE:
                self.DONE.emit()

        def emit_cancel(self, x, y, action):
            """Emit a CANCEL event by clicking the mouse.

            This is equivalent to pressing the ESC button."""
            if action == RELEASE:
                self.CANCEL.emit()

        def draw_state_rect(self, x, y):
            """Store the pos and draw a rectangle to it."""
            self.state = x, y
            drawRect(self.statex, self.statey, x, y)

        def mouse_pick(self, x, y, action):
            """Process mouse events during interactive picking.

            On PRESS, record the mouse position.
            On MOVE, create a rectangular picking window.
            On RELEASE, pick the objects inside the rectangle.
            """
            if action == PRESS:
                self.makeCurrent()
                self.update()
                pf.app.processEvents()
                self.begin_2D_drawing()
                #self.swapBuffers()
                GL.glEnable(GL.GL_COLOR_LOGIC_OP)
                # An alternative is GL_XOR #
                GL.glLogicOp(GL.GL_INVERT)
                # Draw rectangle
                self.draw_state_rect(x, y)
                self.swapBuffers()

            elif action == MOVE:
                # Remove old rectangle
                self.swapBuffers()
                self.draw_state_rect(*self.state)
                # Draw new rectangle
                self.draw_state_rect(x, y)
                self.swapBuffers()

            elif action == RELEASE:
                GL.glDisable(GL.GL_COLOR_LOGIC_OP)
                self.swapBuffers()
                self.end_2D_drawing()

                x, y = (x+self.statex)/2., (y+self.statey)/2.
                w, h = abs(x-self.statex)*2., abs(y-self.statey)*2.
                if w <= 0 or h <= 0:
                   w, h = pf.cfg.get('draw/picksize', (20, 20))
                vp = GL.glGetIntegerv(GL.GL_VIEWPORT)
                self.pick_window = (x, y, w, h, vp)
                self.selection_busy = False

        def draw_state_line(self, x, y):
            """Store the pos and draw a line to it."""
            self.state = x, y
            drawLine(self.statex, self.statey, x, y)

        def mouse_draw_line(self, x, y, action):
            """Process mouse events during interactive drawing.

            On PRESS, record the mouse position.
            On MOVE, draw a line.
            On RELEASE, add the line to the drawing.
            """
            if action == PRESS:
                self.makeCurrent()
                self.update()
                self.begin_2D_drawing()
                self.swapBuffers()
                GL.glEnable(GL.GL_COLOR_LOGIC_OP)
                # An alternative is GL_XOR #
                GL.glLogicOp(GL.GL_INVERT)
                # Draw rectangle
                if self.drawing.size != 0:
                    self.statex, self.statey = self.drawing[-1, -1]
                self.draw_state_line(x, y)
                self.swapBuffers()

            elif action == MOVE:
                # Remove old rectangle
                self.swapBuffers()
                self.draw_state_line(*self.state)
                # Draw new rectangle
                self.draw_state_line(x, y)
                self.swapBuffers()

            elif action == RELEASE:
                GL.glDisable(GL.GL_COLOR_LOGIC_OP)
                #self.swapBuffers()
                self.end_2D_drawing()

                self.drawn = asarray([[self.statex, self.statey], [x, y]])
                self.drawing_busy = False

        @classmethod
        def has_modifier(clas, e, mod):
            return ( e.modifiers() & mod ) == mod

        def mousePressEvent(self, e):
            """Process a mouse press event."""
            # Make the clicked viewport the current one
            pf.GUI.viewports.setCurrent(self)
            # on PRESS, always remember mouse position and button
            self.statex, self.statey = e.x(), self.height()-e.y()
            self.button = e.button()
            self.mod = e.modifiers() & ALLMODS
            #imod = int(self.mod)
            #bmod = "{:032b}".format(imod)
            #print("PRESS BUTTON %s WITH MODIFIER %s(%s)" % (self.button,bmod,imod))
            func = self.getMouseFunc()
            if func:
                func(self.statex, self.statey, PRESS)
            e.accept()

        def mouseMoveEvent(self, e):
            """Process a mouse move event."""
            # the MOVE event does not identify a button, use the saved one
            func = self.getMouseFunc()
            if func:
                func(e.x(), self.height()-e.y(), MOVE)
            e.accept()

        def mouseReleaseEvent(self, e):
            """Process a mouse release event."""
            func = self.getMouseFunc()
            self.button = None        # clear the stored button
            if func:
                func(e.x(), self.height()-e.y(), RELEASE)
            e.accept()

        def wheelEvent(self, e):
            """Process a wheel event."""
            func = self.wheel_zoom
            if func:
                func(e.delta())
            e.accept()

        # Any keypress with focus in the canvas generates a GUI WAKEUP signal.
        # This is used to break out of a wait status.
        # Events not handled here could also be handled by the toplevel
        # event handler.
        def keyPressEvent (self, e):
            # Make the clicked viewport the current one
            pf.GUI.signals.WAKEUP.emit()
            if e.key() == ESC:
                self.CANCEL.emit()
                e.accept()
            elif e.key() == ENTER or e.key() == RETURN:
                self.DONE.emit()
                e.accept()
            else:
                e.ignore()

    ################# Multiple Viewports ###############

    class NewMultiCanvas(QtWidgets.QGridLayout):
        """An OpenGL canvas with multiple viewports and QT interaction.

        The MultiCanvas implements a central QT widget containing one or more
        QtCanvas widgets.
        """
        def __init__(self,parent=None):
            """Initialize the multicanvas."""
            QtWidgets.QGridLayout.__init__(self)
            self.all = []
            self.current = None
            self.rowwise = True
            self.parent = parent

        def changeLayout(self,nvps=None,ncols=None,nrows=None,pos=None,rstretch=None,cstretch=None):
            """Change the lay-out of the viewports on the OpenGL widget.

            nvps: number of viewports
            ncols: number of columns
            nrows: number of rows
            pos: list holding the position and span of each viewport
            [[row,col,rowspan,colspan],...]
            rstretch: list holding the stretch factor for each row
            cstretch: list holding the stretch factor for each column
            (rows/columns with a higher stretch factor take more of the
            available space)
            Each of this parameters is optional.

            If pos is given, it specifies all viewports and nvps, nrows and ncols
            are disregarded.

            Else:

            If nvps is given, it specifies the number of viewports in the layout.
            Else, nvps will be set to the current number of viewports.

            If ncols is an int, viewports are laid out rowwise over ncols
            columns and nrows is ignored. If ncols is None and nrows is an int,
            viewports are laid out columnwise over nrows rows.

            If nvps is not equal to the current number of viewports, viewports
            will be added or removed to match the requested number.

            By default they are laid out rowwise over two columns.
            """
            if pos is None:
                # get the new layout definition
                if nvps is None:
                    nvps = len(self.all)
                if ncols is None:
                    if nrows is None:
                        ncols = self.ncols()
                if isInt(ncols):
                    pos = [ divmod(i, ncols) for i in range(nvps) ]
                elif isInt(nrows):
                    pos = [ divmod(i, nrows)[::-1] for i in range(nvps) ]
                else:
                    return
            else:
                nvps = len(pos)

            while len(self.all) < nvps:
                # create new viewports
                view = self.createView()
                self.all.append(view)

            while len(self.all) > nvps:
                # remove viewports
                self.removeView()

            # remove all views from the canvas
            for w in self.all:
                self.removeWidget(w)
               # w.hide()

            # create the new layout
            for view, args in zip(self.all, pos):
                self.addView(view,*args)
            self.setCurrent(self.all[-1])

        def createView(self,shared=None):
            """Create a new viewport

            If another QtCanvas instance is passed, both will share the same
            display lists and textures.
            """
            if shared is not None:
                pf.debug("SHARING display lists WITH %s" % shared, pf.DEBUG.DRAW)
            view = QtCanvas(self.parent, shared)
            if len(self.all) > 0:
                # copy default settings from previous
                view.resetDefaults(self.all[-1].settings)
            return(view)

        def addView(self,view,row,col,rowspan=1,colspan=1):
            """Add a new viewport and make it visible"""
            self.addWidget(view, row, col, rowspan, colspan)
            view.raise_()
            view.initializeGL()   # Initialize OpenGL context and camera

        def removeView(self,view=None):
            """Remove a view from the canvas

            If view is None, the last one is removed.
            You can not remove a view when there is only one left.
            """
            if len(self.all) > 1:
                if view is None:
                    view = self.all.pop()
                else:
                    i = self.all.find(view)
                    if i < 0:
                        return
                    view = self.all.pop(i)
                    if self.current == view:
                        self.setCurrent(self.all[i-1])
                    self.removeWidget(view)
                    view.close()

        def setCurrent(self, view):
            """Make the specified viewport the current one.

            view can be either a viewport or viewport number.
            The current viewport is the one that will be used for drawing
            operations. This may be different from the viewport having GUI
            focus (pf.canvas).
            """
            #print "NEWCANVAS SETTING CURRENT VIEWPORT"
            if isInt(view) and view in range(len(self.all)):
                view = self.all[view]
            if view == self.current:
                return  # already current

            if view in self.all:
                if self.current:
                    self.current.focus = False
                    self.current.updateGL()
                self.current = view
                self.current.focus = True
                self.current.updateGL()

            pf.canvas = pf.GUI.viewports.current

        def currentView(self):
            return self.all.index(self.current)

        def nrows(self):
            return self.rowCount()

        def ncols(self):
            return self.columnCount()

        def setStretch(self, rowstretch, colstretch):
            """Set the row and column stretch factors.

            rowstretch and colstretch are lists of stretch factors to be applied
            on the subsequent rows/columns. If the lists are shorter than the
            number of rows/columns, the
            """
            if rowstretch:
                for i in range(min(len(rowstretch), self.nrows())):
                    self.setRowStretch(i, rowstretch[i])
            if colstretch:
                for i in range(min(len(colstretch), self.ncols())):
                    self.setColumnStretch(i, colstretch[i])

        def updateAll(self):
             pf.debug("UPDATING ALL VIEWPORTS", pf.DEBUG.GUI)
             for v in self.all:
                 v.update()
             pf.GUI.processEvents()

        def printSettings(self):
            for i, v in enumerate(self.all):
                print("""
    ## VIEWPORTS ##
    Viewport %s;  Current:%s;  Settings:
    %s
    """ % (i, v == self.current, v.settings))

        def link(self, vp, to):
            """Link viewport vp to to"""
            print("LINK %s to %s" % (vp, to))
            print("LINKING CURRENTLY DISABLED")
            return
            nvps = len(self.all)
            if vp in range(nvps) and to in range(nvps) and vp != to:
                to = self.all[to]
                oldvp = self.all[vp]
                utils.warn('warn_viewport_linking')
                newvp = self.newView(to)
                self.all[vp] = newvp
                self.removeWidget(oldvp)
                oldvp.close()
                self.showWidget(newvp)
                vp = newvp
                vp.scene = to.scene
                vp.show()
                vp.setCamera()
                vp.redrawAll()
                #vp.updateGL()
                pf.GUI.processEvents()

    class FramedGridLayout(QtWidgets.QGridLayout):
        """A QtWidgets.QGridLayout where each added widget is framed."""

        def __init__(self,parent=None):
            """Initialize the multicanvas."""
            QtWidgets.QGridLayout.__init__(self)
            self.setContentsMargins(0, 0, 0, 0)
    #       self.frames = []

        def addWidget(*args):
    #        f = QtWidgets.QFrame(w)
    #        self.frames.append(f)
            QtWidgets.QGridLayout.addWidget(*args)

        def removeWidget(self, w):
            QtWidgets.QGridLayout.removeWidget(self, w)

    class MultiCanvas(FramedGridLayout):
        """An OpenGL canvas with multiple viewports and QT interaction.

        The MultiCanvas implements a central QT widget containing one or more
        QtCanvas widgets.
        """
        def __init__(self,parent=None):
            """Initialize the multicanvas."""
            FramedGridLayout.__init__(self)
            self.all = []
            self.current = None
            self.ncols = 2
            self.rowwise = True
            self.pos = None
            self.rstretch = None
            self.cstretch = None
            self.parent = parent

        def newView(self,shared=True,settings=None):
            """Create a new viewport.

            If shared is True, and the MultiCanvas already has one or more
            viewports, the new viewport will share display lists and textures
            with the first viewport. Since pyFormex is not using display
            lists (anymore) and textures are needed to display text, the value
            defaults to True, and all viewports will share the same textures,
            unless a viewport is created with a specified value for shared:
            it can either be another viewport to share textures with, or a
            value False or None to not share textures with any viewport. In the
            latter case you will not be able to use text display, unless you
            initialize the textures yourself.

            settings: can be a legal CanvasSettings to initialize the viewport.
            Default is to copy settings of the current viewport.

            Returns the created viewport, which is an instance of QtCanvas.
            """
            if not isinstance(shared,QtCanvas):
                if shared and len(self.all) > 0:
                    shared = self.all[0]
                else:
                    shared = None

            # Now shared should be a QtCanvas or None
            pf.debug("New viewport sharing textures with %s" % shared, pf.DEBUG.DRAW)
            if settings is None:
                try:
                    settings = self.current.settings
                except:
                    settings = {}
            pf.debug("Create new viewport with settings:\n%s"%settings, pf.DEBUG.CANVAS)
            ##
            ## BEWARE: shared should be positional, settings should be keyword !
            canv = QtCanvas  (self.parent, shared, settings=settings)
            #print(canv.settings)
            return(canv)

        def addView(self):
            """Add a new viewport to the widget"""
            canv = self.newView()
            if len(self.all) > 0:
                # copy default settings from previous
                canv.resetDefaults(self.all[-1].settings)
            self.all.append(canv)
            self.showWidget(canv)
            canv.initializeGL()   # Initialize OpenGL context and camera
            self.setCurrent(canv)

        def setCurrent(self, canv):
            """Make the specified viewport the current one.

            canv can be either a viewport or viewport number.
            """
            #print "SETTING CURRENT VIEWPORT"
            if isInt(canv) and canv in range(len(self.all)):
                canv = self.all[canv]
            if canv == self.current:
                #print "ALREADY CURRENT"
                pass
            elif canv in self.all:
                #print "CHANGING CURRENT"
                if self.current:
                    self.current.focus = False
                    self.current.updateGL()
                self.current = canv
                self.current.focus = True
                self.current.updateGL()
                toolbar.updateViewportButtons(self.current)

            pf.canvas = self.current

        def viewIndex(self, view):
            """Return the index of the specified view"""
            return self.all.index(view)

        def currentView(self):
            return self.all.index(self.current)

        def showWidget(self, w):
            """Show the view w."""
            ind = self.all.index(w)
            if self.pos is None:
                row, col = divmod(ind, self.ncols)
                if not self.rowwise:
                    row, col = col, row
                rspan, cspan = 1, 1
            elif ind < len(self.pos):
                row, col, rspan, cspan = self.pos[ind]
            else:
                return
            self.addWidget(w, row, col, rspan, cspan)
            w.raise_()
            # set the stretch factors
            if self.rstretch is not None:
                for i in range(row, row+rspan):
                    if i >= len(self.rstretch):
                        self.rstretch.append(1)
                    self.setRowStretch(i, self.rstretch[i])
            if self.cstretch is not None:
                for i in range(col, col+cspan):
                    if i >= len(self.cstretch):
                        self.cstretch.append(1)
                    self.setColumnStretch(i, self.cstretch[i])

        def removeView(self):
            if len(self.all) > 1:
                w = self.all.pop()
                if self.pos is not None:
                    self.pos = self.pos[:-1]
                if self.current == w:
                    self.setCurrent(self.all[-1])
                self.removeWidget(w)
                w.close()
                # set the stretch factors
                pos = [self.getItemPosition(self.indexOf(w)) for w in self.all]
                if self.rstretch is not None:
                    row = max([p[0]+p[2] for p in pos])
                    for i in range(row, len(self.rstretch)):
                        self.setRowStretch(i, 0)
                    self.rstretch = self.rstretch[:row]
                if self.cstretch is not None:
                    col = max([p[1]+p[3] for p in pos])
                    for i in range(col, len(self.cstretch)):
                        self.setColumnStretch(i, 0)
                    self.cstretch = self.cstretch[:col]

    ##     def setCamera(self,bbox,view):
    ##         self.current.setCamera(bbox,view)

        def updateAll(self):
             pf.debug("UPDATING ALL VIEWPORTS", pf.DEBUG.GUI)
             for v in self.all:
                 v.update()
             pf.GUI.processEvents()

        def printSettings(self):
            for i, v in enumerate(self.all):
                print("""
    ## VIEWPORTS ##
    Viewport %s;  Current:%s;  Settings:
    %s
    """ % (i, v == self.current, v.settings))

        def changeLayout(self,nvps=None,ncols=None,nrows=None,pos=None,rstretch=None,cstretch=None):
            """Change the lay-out of the viewports on the OpenGL widget.

            nvps: number of viewports
            ncols: number of columns
            nrows: number of rows
            pos: list holding the position and span of each viewport
            [[row,col,rowspan,colspan],...]
            rstretch: list holding the stretch factor for each row
            cstretch: list holding the stretch factor for each column
            (rows/columns with a higher stretch factor take more of the
            available space)
            Each of this parameters is optional.

            If a number of viewports is given, viewports will be added
            or removed to match the requested number.
            By default they are laid out rowwise over two columns.

            If ncols is an int, viewports are laid out rowwise over ncols
            columns and nrows is ignored. If ncols is None and nrows is an int,
            viewports are laid out columnwise over nrows rows. Alternatively,
            the pos argument can be used to specify the layout of the viewports.
            """
            # add or remove viewports to match the requested number
            if isInt(nvps):
                while len(self.all) > nvps:
                    self.removeView()
                while len(self.all) < nvps:
                    self.addView()
            # get the new layout definition
            if isInt(ncols):
                rowwise = True
                pos = None
            elif isInt(nrows):
                ncols = nrows
                rowwise = False
                pos = None
            elif isinstance(pos, list) and len(pos) == len(self.all):
                ncols = None
                rowwise = None
            else:
                return
            # remove the viewport widgets
            for w in self.all:
                self.removeWidget(w)
            # assign the new layout arguments
            self.ncols = ncols
            self.rowwise = rowwise
            self.pos = pos
            self.rstretch = rstretch
            self.cstretch = cstretch
            # add the viewport widgets
            for w in self.all:
                self.showWidget(w)

        def link(self, vp, to):
            """Link viewport vp to to"""
            print("LINK %s to %s" % (vp, to))
            nvps = len(self.all)
            if vp in range(nvps) and to in range(nvps) and vp != to:
                to = self.all[to]
                oldvp = self.all[vp]
                utils.warn('warn_viewport_linking')
                newvp = self.newView(shared=True)
                self.all[vp] = newvp
                self.removeWidget(oldvp)
                oldvp.close()
                self.showWidget(newvp)
                vp = newvp
                vp.scene.actors = to.scene.actors
                vp.show()
                vp.setCamera()
                vp.redrawAll()
                #vp.updateGL()
                pf.GUI.processEvents()

    def _auto_initialize():
        global MultiCanvas
        try:
            if pf.options.newviewports:
                MultiCanvas = NewMultiCanvas
        except:
            pass

    _auto_initialize()

    # End