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# Glossary

Some of the terms used in this manual may be new to some programmers. It is hoped that this appendix sheds some light on these terms.

bitmapped image
  An image that is stored as 2-dimensional array of bits (hence bit-map) or pixels. This image may be written directly to the screen/canvas.

callback
  A function which should be called when something happens. This function is registered ahead of time. The use of callbacks makes event-driven programming much more simple and robust.

canvas
  A region on the screen or in a window into which you can draw things.

event-driven
  A term for a programming methodology which is based on waiting for events, and processing each as it occurs.

event
  A thing which happens, like a button is pressed. Events can by low-level (such as button or keyboard events), or they can be high level (such as when a new dataset is available for processing).

graphics primitive
  A fundamental object that may be drawn onto a canvas, such as a point, a line, an ellipse and so forth. A bitmapped image may also be considered a primitive.

intelligent array
  An array object that knows its own size, dimensionality and its type.

memory mapping
  A technique that avoids reading in an entire file into virtual memory, by ``mapping'' the contents of the file somewhere into your virtual memory space. Once mapped, you can access any portion of the file just as you would when accessing normal memory. The operating system will automatically read into physical memory the section of the mapped file that you access. This allows you to access data at the end of the file without having to read the whole file in. It also means that you don't have to allocate virtual memory (swap space) in order to be able to access all parts of the file.

pixel
  All graphics primitives are drawn to a canvas by writing pixels to specific locations. Pixels may be 8 bits (typical for PseudoColour displays) or 24 bits (for TrueColour and DirectColour displays). Other sizes are possible, but not common.

pixel canvas
  A canvas onto which may be drawn pixel values, in a pixel co-ordinate system.

restriction information
  A way of describing the location of an m-dimensional slice of data in a higher dimensional dataset.

tiled array
  A way of ordering the data in an array so that values which are close to each other in n-dimensional space are also close to each other in memory. The advantage of this storage scheme is that most ways of accessing data become much faster.

window refresh
  The act of redrawing the contents of a window, because something has erased the contents of the window.

world canvas
  A canvas onto which may be drawn pixel values or data values, in a world co-ordinate system. World co-ordinates are possibly non-linear and may even be curvilinear, with some interaction between the two co-ordinate axes.

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