VDU 25
PLOT commands
| Syntax | VDU 25,<numeric>,<numeric>;<numeric>;
|
| Character stream (hex) | &19 <command> <Xlow> <Xhigh> <Ylow> <Yhigh>
|
| Description | Performs a vector graphics operation. |
Coordinates
The X and Y coordinates specify logical points in a logical screen that is the same size in all screen modes with the same aspect ratio regardless of the number of physical pixels. The usual BBC screen size is 1280 horizontal logical pixels by 1024 vertical logical pixels.
Plot commands
The plot command is a bitmap indicating what action to perform.
+---+---+---+---+---+---+---+---+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 0 | Draw line
+---+---+---+---+---+---+---+---+
| | | | | | | |
| | | | | | +---+---00 Move
| | | | | | 01 Plot with foreground GCOL action and colour
| | | | | | 10 Plot in inverse colour as though GCOL 4
| | | | | | 11 Plot with background GCOL action and colour
| | | | | +----------- 0 Relative coordinates
| | | | | 1 Absolute coordinates
| | | | +--------------- 0 Last point not omitted
| | | | 1 Last point omitted
| | | +------------------- 0 Solid line
| | | 1 Dot-dash line
| | +----------------------- 0 First point not omitted
| | 1 First point omitted
+---+---------------------------00 Draw line
+---+---+---+---+---+---+---+---+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 0 | Plot points
+---+---+---+---+---+---+---+---+
| | | | | | | |
| | | | | | +---+---00 Move
| | | | | | 01 Plot with foreground GCOL action and colour
| | | | | | 10 Plot in inverse colour as though GCOL 4
| | | | | | 11 Plot with background GCOL action and colour
| | | | | +----------- 0 Relative coordinates
| | | | | 1 Absolute coordinates
+---+---+---+---+---------------&40+n Plot point
&48+n Fill to non-background
&50+n Fill triangle
&58+n Fill to background
&60+n Fill rectangle
&68+n Fill to foreground
&70+n Fill parallelogram
&78+n Fill to non-foreground
+---+---+---+---+---+---+---+---+
| 7 | 6 | 5 | 4 | 3 | 2 | 1 0 | Fill area and other actions
+---+---+---+---+---+---+---+---+
| | | | | | | |
| | | | | | +---+---00 Move
| | | | | | 01 Plot with foreground GCOL action and colour
| | | | | | 10 Plot in inverse colour as though GCOL 4
| | | | | | 11 Plot with background GCOL action and colour
| | | | | +----------- 0 Relative coordinates
| | | | | 1 Absolute coordinates
+---+---+---+---+---------------&80+n Flood to non-background
&88+n Flood to foreground
&90+n Circle outline
&98+n Circle fill
&A0+n Circle arc
&A8+n Circle segment
&B0+n Circle sector
&B8+n Block copy/move/swap:
b0-b1: 00 no action
01 copy
10 move
11 swap (copy and move)
&C0+n Ellipse outline
&C8+n Ellipse fill
&D0+n Font plot
&D8+n Reserved
&E0+n Reserved
&E8+n Sprite plot (BBFW: block swap)
&F0+n User plot
&F8+n User plot
Calling from BBC BASIC
PLOT k,x,y sends VDU 25,k,x;y; MOVE x,y sends PLOT 4,x,y DRAW x,y sends PLOT 5,x,y On BASICs that support the commands: MOVE BY x,y sends PLOT 0,x,y DRAW BY x,y sends PLOT 1,x,y PLOT BY x,y sends PLOT 65,x,y PLOT x,y sends PLOT 69,x,y FILL BY x,y sends PLOT 129,x,y FILL x,y sends PLOT 133,x,y LINE x1,y1,x2,y2 sends MOVE x1,y1:DRAW x2,y2 CIRCLE x,y,r sends MOVE x,y:PLOT 145,r,0 CIRCLE FILL x,y,r sends MOVE x,y:PLOT 153,r,0 ELLIPSE x,y,a,b sends MOVE x,y:MOVE a,0:PLOT 193,0,b ELLIPSE FILL x,y,a,b sends MOVE x,y:MOVE a,0:PLOT 201,0,b RECTANGLE FILL x,y,w,h sends MOVE x,y:PLOT 101,x+w,y+h RECTANGLE FILL x1,y1,w,h TO x2,y2 sends MOVE x1,y1:MOVE x1+w,y1+h:PLOT 189,x2,y2 RECTANGLE x1,y1,w,h TO x2,y2 sends MOVE x1,y1:MOVE x1+w,y1+h:PLOT 190,x2,y2 RECTANGLE SWAP x1,y1,w,h TO x2,y2 sends MOVE x1,y1:MOVE x1+w,y1+h:PLOT 191,x2,y2 RECTANGLE x,y,w,h sends MOVE x,y:PLOT 13,x+w,y:PLOT 13,x+w,y+h:PLOT 13,x,y+h:PLOT 13,x,y
Implementation
| PLOT &00-&3F | Draw line | All platforms |
| PLOT &40+n | Plot point | All platforms |
| PLOT &48+n | Fill to non-background | All platforms |
| PLOT &50+n | Draw trangle | All platforms |
| PLOT &58+n | Fill to background | |
| PLOT &60+n | Fill rectangle | |
| PLOT &68+n | Fill to foreground | |
| PLOT &70+n | Fill parallelogram | |
| PLOT &78+n | Fill to non-foreground | |
| PLOT &80+n | Flood to non-background | |
| PLOT &88+n | Flood to foreground | |
| PLOT &90+n | Circle outline | |
| PLOT &98+n | Circle fill | |
| PLOT &A0+n | Circle arc | |
| PLOT &A8+n | Circle segment | |
| PLOT &B0+n | Circle sector | |
| PLOT &B8+n | Block copy/move/swap | |
| PLOT &C0+n | Ellipse outline | |
| PLOT &C8+n | Ellipse fill | |
| PLOT &D0+n | Font plot | |
| PLOT &D8+n | Reserved | |
| PLOT &E0+n | Reserved | |
| PLOT &E8+n | Sprite plot | |
| PLOT &F0+n | User | All platforms |
| PLOT &F8+n | User | All platforms |
