[Mesa-dev] [alternate PATCH 1.1/6] mesa: Handle GL_BACK correctly for ES 3.0 in glDrawBuffers().

[Anuj Phogat]

On Tue, Dec 18, 2012 at 1:26 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
> In ES 3.0, when calling glDrawBuffers() on the window system
> framebuffer, the only valid targets are GL_NONE or GL_BACK.  Since there
> is no stereo rendering in ES 3.0, this is a single buffer, unlike
> desktop where it may be two (and thus isn't allowed).
>
> For single-buffered configs, GL_BACK ironically means the front (and
> only) buffer.  I'm not sure that it matters, however, as ES shouldn't
> have front buffer rendering in the first place.
>
> Fixes es3conform framebuffer_blit_coverage_default_draw_buffer_binding.
> ---
>  src/mesa/main/buffers.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
>
> These two patches are a proposed replacement for Anuj's patch 1/6.
>
patch 1/6 is still required to fix failures related to
glGetFramebufferAttachmentParameteriv
in framebuffer_blit_functionality_multisampled_to_singlesampled_blit test case.
I'll soon post an updated patch.

> diff --git a/src/mesa/main/buffers.c b/src/mesa/main/buffers.c
> index aa9b9f0..244f4de 100644
> --- a/src/mesa/main/buffers.c
> +++ b/src/mesa/main/buffers.c
> @@ -94,7 +94,7 @@ supported_buffer_bitmask(const struct gl_context *ctx,
>   * GL_FRONT_AND_BACK), return the corresponding bitmask of BUFFER_BIT_* flags.
>   */
>  static GLbitfield
> -draw_buffer_enum_to_bitmask(GLenum buffer)
> +draw_buffer_enum_to_bitmask(const struct gl_context *ctx, GLenum buffer)
>  {
>     switch (buffer) {
>        case GL_NONE:
> @@ -102,6 +102,19 @@ draw_buffer_enum_to_bitmask(GLenum buffer)
>        case GL_FRONT:
>           return BUFFER_BIT_FRONT_LEFT | BUFFER_BIT_FRONT_RIGHT;
>        case GL_BACK:
> +         if (_mesa_is_gles3(ctx)) {
> +            /* From the ES 3.0 specification, page 180:
> +             * "When draw buffer zero is BACK, color values are written into
> +             *  the sole buffer for single-buffered contexts, or into the back
> +             *  buffer for double-buffered contexts."
> +             *
> +             * Since there is no stereo rendering in ES 3.0, only return the
> +             * LEFT bits.  This also satisfies the "n must be 1" requirement.
> +             */
> +            if (ctx->DrawBuffer->Visual.doubleBufferMode)
> +               return BUFFER_BIT_BACK_LEFT;
> +            return BUFFER_BIT_FRONT_LEFT;
> +         }
>           return BUFFER_BIT_BACK_LEFT | BUFFER_BIT_BACK_RIGHT;
>        case GL_RIGHT:
>           return BUFFER_BIT_FRONT_RIGHT | BUFFER_BIT_BACK_RIGHT;
> @@ -241,7 +254,7 @@ _mesa_DrawBuffer(GLenum buffer)
>     else {
>        const GLbitfield supportedMask
>           = supported_buffer_bitmask(ctx, ctx->DrawBuffer);
> -      destMask = draw_buffer_enum_to_bitmask(buffer);
> +      destMask = draw_buffer_enum_to_bitmask(ctx, buffer);
>        if (destMask == BAD_MASK) {
>           /* totally bogus buffer */
>           _mesa_error(ctx, GL_INVALID_ENUM,
> @@ -321,7 +334,7 @@ _mesa_DrawBuffers(GLsizei n, const GLenum *buffers)
>              return;
>           }
>
> -         destMask[output] = draw_buffer_enum_to_bitmask(buffers[output]);
> +         destMask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
>
>           /* From the OpenGL 3.0 specification, page 258:
>            * "Each buffer listed in bufs must be one of the values from tables
> @@ -451,7 +464,7 @@ _mesa_drawbuffers(struct gl_context *ctx, GLuint n, const GLenum *buffers,
>        const GLbitfield supportedMask = supported_buffer_bitmask(ctx, fb);
>        GLuint output;
>        for (output = 0; output < n; output++) {
> -         mask[output] = draw_buffer_enum_to_bitmask(buffers[output]);
> +         mask[output] = draw_buffer_enum_to_bitmask(ctx, buffers[output]);
>           ASSERT(mask[output] != BAD_MASK);
>           mask[output] &= supportedMask;
>        }
> --
> 1.8.0.2
>
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Reviewed-by: Anuj Phogat <anuj.phogat at gmail.com>