Plot Commands :
0 Solid line incl end pts 8 excl end pt
16 Dotted line incl end pts 24 excl end pt
32 Solid line excl first pt 40 excl both end pts
48 Dotted line excl first pt, 56 excl both end pts
pattern continued
Horizontal linefill:
64 Point plot 72 (left&right) to non backgr
80 Triangle fill 88 (to right) to backgr
96 Rectangle fill 104 (left&right) to foregr
112 Parallelogram fill 120 (to right) to non foregr
128 Flood to non-background 136 Flood to foreground
144 Circle outline 152 Circle fill
160 Circular arc 168 Segment
176 Sector 184 Block copy/move
192 Ellipse outline 200 Ellipse fill
208 Font printing (don't use) 232 Sprite Plot
The base commands are specified in the top 5 bits, modified by the value in the bottom 3 bits . Block copy/move uses a special set of modifiers .
Some shapes need to be defined by a sequence of points. The VDU drivers use the previous positions of the graphics cursor to define these. These can be specified by a sequence of absolute or relative moves (commands 64 or 68) - the points to visit to define a particular shape is given as a link in the table above.
Unknown plot codes (216-231,240-255) are sent to the unknown plot vector, which by default does nothing.
The dash pattern is set with VDU 23,6 and can be read with OS_Word 10,6. Its length is set and read with OS_Byte 163.
Line Moves
To plot a line, move to one endpoint, then plot line to other endpoint
Triangle Moves
To plot a triangle, move to vertex, move to next vertex, then plot triangle to third vertex.
Rectangle Moves
To plot a rectangle, move to one corner, then plot rectangle to diagonally opposite corner.
Parallelogram Moves
To plot a parallelogram, move to vertex, move to next vertex, then plot parallelogram to third vertex. Fourth vertex will be opposite second.
Circle Moves
To plot a circle, move to centre, then plot circle to a point on the circumference.
Arc/Segment/Sector Moves
To plot an arc/segment/sector, move to centre, move to start, then plot arc/segment/sector to a point on the line joining centre to end. Arc/segment/sector will be plotted anticlockwise.
Block Copy/Move Moves
First define the source rectangle: move to one corner, then move to diagonally opposite corner. Then plot bottom left corner of destination.
Ellipse Moves
To plot a ellipse, move to centre, move to point on circumference with same Y coord as centre, then plot ellipse to the lowest or highest point on the circumference.
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