Text viewports and sprites
Monday, 21st July 2008
Back to work on the TI-83 Plus port of BBC BASIC! To complement the graphics viewport I've added support for text viewports — this lets you define the area the text console uses. The following VDU commands are now supported:
- VDU 24,<left>;<top>;<right>;<bottom>;
Define a graphics viewport. - VDU 28,<left>,<top>,<right>,<bottom>
Define a text viewport. - VDU 26
Reset both viewports to their default settings (full screen). - VDU 29,<x>;<y>;
Defines the graphics origin.
![2008.07.13.01.gif](/bin/bbcbasic/2008.07.13.01.gif)
The above screenshots defines the graphics viewport to fill the left hand side of the screen and shunts the text viewport over to the right half, using the following code:
VDU 24,0;0;47;63; VDU 28,12,0,23,9 VDU 29,24;32;I've also added simple sprite drawing to BBC BASIC's PLOT command. PLOT usually takes a shape type and two coordinates, but for sprites (shapes 208..215) I've added an extra parameter - the address of the sprite data to use.
![2008.07.20.01.gif](/bin/bbcbasic/2008.07.20.01.gif)
10 DIM ball 7 20 ball?0=&3C 30 ball?1=&5E 40 ball?2=&8F 50 ball?3=&DF 60 ball?4=&FF 70 ball?5=&FF 80 ball?6=&7E 90 ball?7=&3C 100 *REFRESH OFF 110 REPEAT 120 CLG 130 T=TIME/100 140 FOR P=0 TO 5 150 A=P/3*PI+T 160 X=16*SIN(A)+44 170 Y=16*COS(A)+28 180 PLOT 213,X,Y,ball 190 NEXT 200 *REFRESH 210 UNTIL INKEY(0)<>-1 220 *REFRESH ON
The above code allocates 8 bytes of memory (DIM ball 7) then copies the sprite data to it by use of the ? indirection operator. This is a little laborious, so in reality you'd probably store your sprites in a binary file external to the main program, and might load them like this:
10 ball%=FN_loadSprite("SPRITES",0) 20 face%=FN_loadSprite("SPRITES",1) 30 *REFRESH OFF 40 REPEAT 50 CLG 60 T=TIME/100 70 FOR P=0 TO 5 80 A=P/3*PI+T 90 X=16*SIN(A)+44 100 Y=16*COS(A)+28 110 PLOT 213,X,Y,ball% 120 NEXT 130 PLOT 213,44,28,face% 140 *REFRESH 150 UNTIL INKEY(0)<>-1 160 *REFRESH ON 170 END 180 DEF FN_loadSprite(f$,i%) 190 fh%=OPENIN(f$) 200 PTR#fh%=i%*8 210 DIM spr 7 220 FOR j%=0 TO 7 230 spr?j%=BGET#fh% 240 NEXT j% 250 CLOSE#fh% 260 =spr 270 ENDPROC
(Note FN_loadSprite() at the end of the program). The result is the following:
![2008.07.20.02.gif](/bin/bbcbasic/2008.07.20.02.gif)
Next up: drawing text at the graphics cursor position (as sprites).