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Color Computer 2 semi-graphics mode 8

Posted by hloberg, in programming, coco2 16 February 2019 · 93 views

COCO2 COLOR COMPUTER GRAHICS PROGRAMMING TANDY RADIO SHACK


 
this is a short blog. Again playing around with the Color Computer 2 & came across the semi-graphic mode 8. This mode isn't really addressable straight from BASIC. You have to do a series of POKES and address the screen by the location in memory, but it still has potential. you can display all 9 color on the screen in a 32 x 64 grid. With a little assembler trickery I can see that being expanded to 64 x 64. Semi-graphics mode 24 can give you 64 x 128, not bad. 
Who ever wrote the Wikipedia article on the CoCo2 referred to these modes as 'interesting curiosity'. Personally I think that you could do some good graphics and games with these modes. He also complains that the screen occupies up to 6k. Well, Atari GITA modes that produce up to 8 color or 16 shades/hues takes up 8k and the pixels are about the same size, roughly, Now Atari GITA is directly accessible in BASIC and doesn't need some half character tricks to make the pixels 4 pips wide, so you have that. Still, 9 color on the screen in a raster graphic? Not many computers of the era was able to do that. 
 here is the code:
10 REM SGM 8
15 POKE 65495,0 :REM SPEED UP
17 REM CREATE SG 8
20 POKE 65314,(PEEK(65314) AND 7):POKE 65479,0:POKE 65481,0:POKE 65483,0:POKE 65476,0
30 POKE 65475,0:POKE 65472,0
40 REM 64X64 - 8 COLOR
50 REM POKE 3584-5632
60 FOR I=3584 TO 4984 :REM BLACK SCREEN
62 POKE I,240
80 NEXT I
90 FOR X=1 TO 64
95 FOR J=0 TO 7
96 G=255-(J*16)
110 POKE (3584+J+X)+(X*32),G
115 NEXT J
200 NEXT X
1000 GOTO 1000 






On the original CoCo there were a whole whack of modes which could be generated by setting the SAM and VDG properly.  IIRC the main issue with them was the horizontal resolution was limited as you were using text graphics.  Back in the day I had the Technical Manual for the CoCo which went into gory detail on the various off-the-shelf chips in the CoCo and what they could do.

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