[Mesa-dev] [PATCH 1/2] st/mesa: adjust blending modes if we don't have destination alpha
Ilia Mirkin
imirkin at alum.mit.edu
Tue Apr 28 17:45:23 PDT 2015
if (blend_per_rt(ctx) || colormask_per_rt(ctx)) {
num_state = ctx->Const.MaxDrawBuffers;
blend->independent_blend_enable = 1;
}
So independent blend won't get enabled even though the backend
supports it in the case where you have the same settings but with one
RGB and one RGBA target.
My concern is that this might end up messing up scenarios that work
today (e.g. when the driver properly supports RGBX and RGBA, but
you'll end up forcing the RGBX one to be ONE instead of DST_ALPHA).
On Tue, Apr 28, 2015 at 8:19 PM, Brian Paul <brianp at vmware.com> 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.
>
> v2: use the i-th (not j-th) render buffer's base format
> ---
> 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..6337e1c 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 i-th render target */
> + rb = ctx->DrawBuffer->_ColorDrawBuffers[i];
> + 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 */
> --
> 1.9.1
>
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