Re: [cc65] Colormania (was: TGI summary)

Hi!

On Tue, Oct 27, 2009 at 4:37 PM, Ullrich von Bassewitz <uz@musoftware.de> wrote:
>
> On Tue, Oct 27, 2009 at 04:19:57PM -0300, Daniel Serpell wrote:
>> The problem with the above is that a program that is designed to
>> run on the Atari mode 9 normally expects index 0 to be black and
>> index 15 to be white, with all the 14 grays in between, and this
>> mapping will break the expectations.
>
> I cannot see a problem with that, since cc65 is not (any more) an Atari
> compiler. For a casual programmer, it is probably more important to have a
> program run on another machine without much trouble. An Atari hardcode
> programmer on the other side has no problem to change the palette.
>

But then, having a tgi driver for mode 9 has little sense, better use one of
the other modes (hires of 4-color).

>> Perhaps a new api could be designed modeled on, for example,
>> how X11 works:
>
> Please come back to the ground:-) We're talking about 6502 machines with some
> 10KB of memory. And TGI is the "Tiny Graphics Interface". It was designed to
> dive into simple graphics programming rather quickly. It was never designed as
> a competitor to OpenGL or DirectX.

Yes, I know :-)

But perhaps a simpler implementation, using the color definitions
can be implemented, like:

unsigned char black = tgi_alloc_color(COLOR_BLACK);
unsigned char white = tgi_alloc_color(COLOR_WHITE);
// ....

Then, the implementation is only a few bytes:

   ; See if the color is already allocated
   ldx #0
SEARCH:
   cmp PALETTE,x
   beq  OK
   inx
   cpx ALOC_COLORS
   bne SEARCH
   ; Color not allocated already.
   cpx #MAX_COLORS
   beq ERR ; No more palette entries available
   sta PALETTE,x
   ; Now, set the palette ... hardware dependent
   inc ALOC_COLORS
OK:
   txa
   rts
ERR:
   lda #255 ; Return 255 on error
   rts

So, it's about 30 bytes for the full definition. And instead of
a tgi_free_color, simply a "tgi_free_all_colors" that sets ALOC_COLORS
back to 0.

Also, in Atari, the already existing COLOR_XXX macros list
palette color values, so the implementation above is complete
if using the OS shadow palette registers as PALETTE.

    Daniel.
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