[Mesa-dev] [Mesa-stable] [PATCH 2/2] meta: Write color values in to 'out' variables for all the draw buffers

[Chris Forbes]

If you're going to do that, you'd really want to add draw buffer count
to the cache key (and i guess this might be the point where you
convert the blit shader cache to be a hashtable), to avoid recompiling
all the time if the app does two blits with the same target but
different draw buffer counts.

This all seems like a huge amount of extra machinery to avoid using
gl_FragColor and having the backend just take care of it, though. What
do we actually gain from this?


On Tue, May 20, 2014 at 10:22 AM, Anuj Phogat <anuj.phogat at gmail.com> wrote:
> On Mon, May 19, 2014 at 3:12 PM, Chris Forbes <chrisf at ijw.co.nz> wrote:
>> On Tue, May 20, 2014 at 8:20 AM, Anuj Phogat <anuj.phogat at gmail.com> wrote:
>>> @@ -247,7 +247,8 @@ _mesa_meta_setup_blit_shader(struct gl_context *ctx,
>>>     struct blit_shader *shader = choose_blit_shader(target, table);
>>>     const char *vs_input, *vs_output, *fs_input, *fs_output;
>>>     const char *vs_preprocess = "", *fs_preprocess = "";
>>> -   const char *fs_output_decl = "";
>>> +   const char *fs_output_decl = "", *for_loop = "";
>>> +   const int draw_buf_count = ctx->DrawBuffer->_NumColorDrawBuffers;
>>
>> You can't depend on the number of bound draw buffers here. These
>> shaders get generated on first use, and cached for the life of the
>> context.
> Nice catch. I'll add a condition to recompile the shader if number of
> draw buffers change.