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.

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;

   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:

Next up: drawing text at the graphics cursor position (as sprites).