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Documented how the TGI API shows when a palette has 256 colors.

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This commit is contained in:
Greg King 2020-06-08 16:39:11 -04:00
parent 20a9c0c336
commit bc1e884988
1 changed files with 22 additions and 2 deletions
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doc/tgi.sgml
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@ -241,14 +241,34 @@ color = tgi_getcolor();
<tag/Function/Get the number of available colors.
<tag/Header/<tt/<ref id="tgi.h" name="tgi.h">/
<tag/Declaration/<tt/unsigned char tgi_getcolorcount (void);/
<tag/Description/Tgi platforms use indexed color palettes. This function
<tag/Description/TGI platforms use indexed color palettes. This function
returns the number of entries we can use in the palette.
<tt/tgi_setcolor()/ can accept numbers from <tt/0/ to <tt/255/. That is 256
possible colors, but an <tt/(unsigned char)/ cannot hold that number.
Therefore, the number zero is used to indicate when a palette has 256 entries.
A portable program should test for that number, and do appropriate actions.
A program might assign the count to an <tt/unsigned int/ (and change a zero to
a 256). Or, it might rely on the fact that <tt/(unsigned char)/ will
"wrap-around" when it is incremented beyond 255.
<tag/Availability/cc65
<tag/See also/Other tgi functions
<tag/Example/<verb>
<tag/Examples/<verb>
if (tgi_getcolorcount() == 2) {
printf("Only monochrome graphics is supported\n");
}
static unsigned char num_colors;
static unsigned char color;
...
num_colors = tgi_getcolorcount();
...
++color;
if (num_colors == 0) {
tgi_setcolor(color);
} else {
tgi_setcolor(color % num_colors);
}
</verb>
</descrip>
</quote>