[Mesa-dev] [PATCH 1/2] st/mesa: adjust blending modes if we don't have destination alpha

[Jose Fonseca]

On 28/04/15 23:16, Brian Paul wrote:
> If the user requested a GL_RGB texture but the driver actually allocated
> an RGBA texture, the alpha values in the texture may not be defined.
>
> If we later bind the texture as a color target and try to blend into
> it with GL_DST_ALPHA or GL_ONE_MINUS_DST_ALPHA we may blend with
> undefined alpha values when, in fact, the dest alpha value should be one.
> So replace GL_DST_ALPHA/GL_ONE_MINUS_DST_ALPHA with GL_ONE/GL_ZERO.
>
> Fixes the piglit fbo-blending-formats test for some GL_RGB formats
> with the VMware driver.  Also tested with llvmpipe.
> ---
>   src/mesa/state_tracker/st_atom_blend.c | 38 +++++++++++++++++++++++++---------
>   1 file changed, 28 insertions(+), 10 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_atom_blend.c b/src/mesa/state_tracker/st_atom_blend.c
> index 6bb4077..30bff7a 100644
> --- a/src/mesa/state_tracker/st_atom_blend.c
> +++ b/src/mesa/state_tracker/st_atom_blend.c
> @@ -44,10 +44,21 @@
>   /**
>    * Convert GLenum blend tokens to pipe tokens.
>    * Both blend factors and blend funcs are accepted.
> + * \param destBaseFormat  the base format of the render target, such as
> + *                        GL_RGBA, GL_RGB, GL_RED, GL_ALPHA, etc.
>    */
>   static GLuint
> -translate_blend(GLenum blend)
> +translate_blend(GLenum blend, GLenum destBaseFormat)
>   {
> +   /* If we don't have destination alpha and the blend factor is either
> +    * GL_DST_ALPHA or GL_ONE_MINUS_DST_ALPHA then we use
> +    * PIPE_BLENDFACTOR_ONE or _ZERO instead.
> +    */
> +   const bool haveDstA = (destBaseFormat == GL_RGBA ||
> +                          destBaseFormat == GL_ALPHA ||
> +                          destBaseFormat == GL_INTENSITY ||
> +                          destBaseFormat == GL_LUMINANCE_ALPHA);
> +
>      switch (blend) {
>      /* blend functions */
>      case GL_FUNC_ADD:
> @@ -69,7 +80,7 @@ translate_blend(GLenum blend)
>      case GL_SRC_ALPHA:
>         return PIPE_BLENDFACTOR_SRC_ALPHA;
>      case GL_DST_ALPHA:
> -      return PIPE_BLENDFACTOR_DST_ALPHA;
> +      return haveDstA ? PIPE_BLENDFACTOR_DST_ALPHA : PIPE_BLENDFACTOR_ONE;
>      case GL_DST_COLOR:
>         return PIPE_BLENDFACTOR_DST_COLOR;
>      case GL_SRC_ALPHA_SATURATE:
> @@ -91,7 +102,7 @@ translate_blend(GLenum blend)
>      case GL_ONE_MINUS_DST_COLOR:
>         return PIPE_BLENDFACTOR_INV_DST_COLOR;
>      case GL_ONE_MINUS_DST_ALPHA:
> -      return PIPE_BLENDFACTOR_INV_DST_ALPHA;
> +      return haveDstA ? PIPE_BLENDFACTOR_INV_DST_ALPHA : PIPE_BLENDFACTOR_ZERO;
>      case GL_ONE_MINUS_CONSTANT_COLOR:
>         return PIPE_BLENDFACTOR_INV_CONST_COLOR;
>      case GL_ONE_MINUS_CONSTANT_ALPHA:
> @@ -208,14 +219,21 @@ update_blend( struct st_context *st )
>      else if (ctx->Color.BlendEnabled) {
>         /* blending enabled */
>         for (i = 0, j = 0; i < num_state; i++) {
> +         const struct gl_renderbuffer *rb;
> +         GLenum baseFormat;
>
>            blend->rt[i].blend_enable = (ctx->Color.BlendEnabled >> i) & 0x1;
>
>            if (ctx->Extensions.ARB_draw_buffers_blend)
>               j = i;
>
> +         /* _NEW_BUFFERS */
> +         /* Get the base format of the render target */
> +         rb = ctx->DrawBuffer->_ColorDrawBuffers[j];
> +         baseFormat = rb ? rb->_BaseFormat : GL_RGBA;
> +
>            blend->rt[i].rgb_func =
> -            translate_blend(ctx->Color.Blend[j].EquationRGB);
> +            translate_blend(ctx->Color.Blend[j].EquationRGB, baseFormat);
>
>            if (ctx->Color.Blend[i].EquationRGB == GL_MIN ||
>                ctx->Color.Blend[i].EquationRGB == GL_MAX) {
> @@ -225,13 +243,13 @@ update_blend( struct st_context *st )
>            }
>            else {
>               blend->rt[i].rgb_src_factor =
> -               translate_blend(ctx->Color.Blend[j].SrcRGB);
> +               translate_blend(ctx->Color.Blend[j].SrcRGB, baseFormat);
>               blend->rt[i].rgb_dst_factor =
> -               translate_blend(ctx->Color.Blend[j].DstRGB);
> +               translate_blend(ctx->Color.Blend[j].DstRGB, baseFormat);
>            }
>
>            blend->rt[i].alpha_func =
> -            translate_blend(ctx->Color.Blend[j].EquationA);
> +            translate_blend(ctx->Color.Blend[j].EquationA, baseFormat);
>
>            if (ctx->Color.Blend[i].EquationA == GL_MIN ||
>                ctx->Color.Blend[i].EquationA == GL_MAX) {
> @@ -241,9 +259,9 @@ update_blend( struct st_context *st )
>            }
>            else {
>               blend->rt[i].alpha_src_factor =
> -               translate_blend(ctx->Color.Blend[j].SrcA);
> +               translate_blend(ctx->Color.Blend[j].SrcA, baseFormat);
>               blend->rt[i].alpha_dst_factor =
> -               translate_blend(ctx->Color.Blend[j].DstA);
> +               translate_blend(ctx->Color.Blend[j].DstA, baseFormat);
>            }
>         }
>      }
> @@ -285,7 +303,7 @@ update_blend( struct st_context *st )
>   const struct st_tracked_state st_update_blend = {
>      "st_update_blend",					/* name */
>      {							/* dirty */
> -      (_NEW_COLOR | _NEW_MULTISAMPLE),  /* XXX _NEW_BLEND someday? */	/* mesa */
> +      (_NEW_BUFFERS | _NEW_COLOR | _NEW_MULTISAMPLE),  	/* mesa */
>         0,						/* st */
>      },
>      update_blend,					/* update */
>

Series LGTM.

Reviewed-by: Jose Fonseca <jfonseca at vmware.com>