VDU 25

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PLOT commands

VDU 25
Syntax VDU 25,<numeric>,<numeric>;<numeric>;
Character stream (hex) &19 <command> <Xlow> <Xhigh> <Ylow> <Yhigh>
Description Performs a vector graphics operation.

Contents

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 in foreground colour
   |   |   |   |   |   |           10    Plot in inverse colour
   |   |   |   |   |   |           11    Plot in background 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 in foreground colour
   |   |   |   |   |   |           10    Plot in inverse colour
   |   |   |   |   |   |           11    Plot in background 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 in foreground colour
   |   |   |   |   |   |           10    Plot in inverse colour
   |   |   |   |   |   |           11    Plot in background 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 x1,y1,w,h TO x2,y2       sends  MOVE x1,y1:MOVE x1+w,y1+h:PLOT 191,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