Graph Units, Pixels, Bitmap Coordinates, Zoom
All function points are first calculated using "Graph Coordinates", they are
then translated into "Pixel Coordinates", and finally into "Bitmap Coordinates"
before being drawn. It is sometimes necessary to work with all three of these
coordinate systems.
Bitmap Coordinates - All graphs are drawn on resizable bitmaps, and displayed in scrolling windows. These bitmaps can be copied and pasted into other programs, or saved to disk. Bitmap coordinates are measured in points or pixels. In bitmap coordinates (0, 0) is the top left corner. The "X" value increases to the right, and the "Y" value increases as you move down. Negative numbers are not allowed.
Pixel Coordinates - Like bitmap coordinates, pixel coordinates are measured in points or pixels. Pixel coordinates work like Cartesian coordinates in all other respects. The origin (center) is at (0, 0). The "X" value increases to the right, and the "Y" value increases as you move up.
Graph Units (Graph Coordinates) - Graph units are used when functions are plotted. They can be expressed as 2D Cartesian, 3D Cartesian, or polar coordinates. Graph units are calculated as "GraphUnits = PixelUnits / Zoom"; this means that graph units change when the zoom changes.
Zoom - The zoom is used to increase or decrease the relative size of a graph and its functions. Bigger zoom values give bigger function graphs. Pixel units are calculated using "PixelUnits = GraphUnits * Zoom". Because of this equation, a zoom greater than 1 will give more than 1 pixel unit per graph unit, and a zoom less than 1 will give multiple graph units per pixel unit. Zoom values must be greater than 0. The 3D graphs allow only integer zoom values. The 2D Cartesian graphs allow for separate "X" and "Y" zoom values.