Hi,

I'm working on a simple Basic program where an bird shaped object/sprite is fired across the screen but am getting an Illegal Quantity Error when the X co-ordinates of the sprite reach 260.

Is anyone able to help (code below)

Also I have drawn a single colour sprite to be overlayed onto the multicolour sprite used above but am not sure how to achieve this (DATA included below) - does anyone have an example listing for both multicolour and single colour sprites?

Thanks
Lee

Code:

30 FOR T= 0 TO 62 40 READ U 50 POKE 12288+T,U 60 NEXT T 65 X=30:REM STARTING X POSITION 66 Y=220: REM STARTING Y POSITION 67 XVEL=8: REM X VELOCITY 68 YVEL=-8: REM Y VELOCITY 70 V=53248 80 POKE 2040,192 90 POKE V,Y:POKE V+1,X 100 POKE V+37,7 110 POKE V+38,1 120 POKE V+39,2 130 POKE V+28,1 140 POKE V+23,0:POKE V+29,0 150 POKE V+21,1 200 PRINT"XVEL" ; XVEL; " X";INT(X) 210 PRINT"YVEL" ; YVEL;" Y";INT(Y) 220 POKE V,INT(X):POKE V+1,INT(Y) 230 X=X+XVEL 231 Y=Y+YVEL 235 IF XVEL > 0 THEN XVEL=XVEL-.10 240 IF Y<210 THEN YVEL=YVEL+.45 245 IF Y>220 THEN YVEL=0 270 GOTO 200 1000 REM DATA FOR COLOUR SPRITE 1010 DATA 0,0,0 1020 DATA 40,168,0 1030 DATA 42,170,0 1040 DATA 10,174,160 1050 DATA 42,175,240 1060 DATA 42,191,240 1070 DATA 170,191,240 1080 DATA 170,191,212 1090 DATA 170,189,213 1100 DATA 170,173,84 1110 DATA 170,169,84 1120 DATA 170,169,84 1130 DATA 170,169,84 1140 DATA 170,169,168 1150 DATA 170,170,168 1160 DATA 42,170,160 1170 DATA 42,170,160 1180 DATA 42,190,160 1190 DATA 10,255,192 1200 DATA 3,255,0 1210 DATA 0,252,0 1220 REM DATA FOR SINGLE COLOUR OVERLAY SPRITE 1240 DATA 0,0,0 1250 DATA 40,168,0 1260 DATA 42,170,0 1270 DATA 10,174,160 1280 DATA 42,175,240 1290 DATA 42,191,240 1300 DATA 170,191,240 1310 DATA 170,191,212 1320 DATA 170,189,213 1330 DATA 170,173,84 1340 DATA 170,169,84 1350 DATA 170,169,84 1360 DATA 170,169,84 1370 DATA 170,169,168 1380 DATA 170,170,168 1390 DATA 42,170,160 1400 DATA 42,170,160 1410 DATA 42,190,160 1420 DATA 10,255,192 1430 DATA 3,255,0 1440 DATA 0,252,0

A memory location can only hold 0-255. So 260 is an illegal quantity.

There are 320 X positions, so how do you get at the last 64?

The sprite MSB or Most Significant Byte. This is is 53264 (V+16).

Like some of the other controls, each bit refers to a sprite. With a single sprite, POKE V+16,1 puts the sprite onto this right hand portion of the screen. POKE V+16,0 puts it back on the left.

One way to do it in your BASIC program would be to add a couple of lines.

260 IF X > 255 THEN MX=1: X=X-256:GOTO200
265 MX=0

And change line 220 to read

220 POKE V,X:POKE V+1,Y:POKEV+16,MX


This means if X is greater than 256, then MX is set to 1 and the sprite will appear on the right. If X is less than 255, MX will be zero and it appears on the left.
_________________

Thanks for that, got myself a copy of a Sprite programming book off Bombjack's excellent book site.

Thanks
Lee