st/mesa: generate blend state according to the number of enabled color buffers

Non-MRT cases always translate blend state for 1 color buffer only.
MRT cases only check and translate blend state for enabled color buffers.

This also avoids an assertion failure in translate_blend for:
  dEQP-GLES31.functional.draw_buffers_indexed.overwrite_common.common_advanced_blend_eq_buffer_blend_eq

Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/state_tracker/st_atom_blend.c

@@ -112,23 +112,26 @@ translate_blend(GLenum blend)
  * Figure out if colormasks are different per rt.
  */
 static GLboolean
-colormask_per_rt(const struct gl_context *ctx)
+colormask_per_rt(const struct gl_context *ctx, unsigned num_cb)
 {
+   GLbitfield full_mask = _mesa_replicate_colormask(0xf, num_cb);
    GLbitfield repl_mask0 =
       _mesa_replicate_colormask(GET_COLORMASK(ctx->Color.ColorMask, 0),
-                                ctx->Const.MaxDrawBuffers);
+                                num_cb);
 
-   return ctx->Color.ColorMask != repl_mask0;
+   return (ctx->Color.ColorMask & full_mask) != repl_mask0;
 }
 
 /**
  * Figure out if blend enables/state are different per rt.
  */
 static GLboolean
-blend_per_rt(const struct gl_context *ctx)
+blend_per_rt(const struct gl_context *ctx, unsigned num_cb)
 {
-   if (ctx->Color.BlendEnabled &&
-      (ctx->Color.BlendEnabled != ((1U << ctx->Const.MaxDrawBuffers) - 1))) {
+   GLbitfield cb_mask = u_bit_consecutive(0, num_cb);
+   GLbitfield blend_enabled = ctx->Color.BlendEnabled & cb_mask;
+
+   if (blend_enabled && blend_enabled != cb_mask) {
       /* This can only happen if GL_EXT_draw_buffers2 is enabled */
       return GL_TRUE;
    }
@@ -144,13 +147,15 @@ st_update_blend( struct st_context *st )
 {
    struct pipe_blend_state *blend = &st->state.blend;
    const struct gl_context *ctx = st->ctx;
+   unsigned num_cb = st->state.fb_num_cb;
    unsigned num_state = 1;
    unsigned i, j;
 
    memset(blend, 0, sizeof(*blend));
 
-   if (blend_per_rt(ctx) || colormask_per_rt(ctx)) {
-      num_state = ctx->Const.MaxDrawBuffers;
+   if (num_cb > 1 &&
+       (blend_per_rt(ctx, num_cb) || colormask_per_rt(ctx, num_cb))) {
+      num_state = num_cb;
       blend->independent_blend_enable = 1;
    }
 

src/mesa/state_tracker/st_atom_framebuffer.c

@@ -216,4 +216,5 @@ st_update_framebuffer_state( struct st_context *st )
    st->state.fb_height = framebuffer.height;
    st->state.fb_num_samples = util_framebuffer_get_num_samples(&framebuffer);
    st->state.fb_num_layers = util_framebuffer_get_num_layers(&framebuffer);
+   st->state.fb_num_cb = framebuffer.nr_cbufs;
 }

src/mesa/state_tracker/st_atom_list.h

@@ -10,7 +10,6 @@ ST_STATE(ST_NEW_VS_STATE, st_update_vp)
 
 ST_STATE(ST_NEW_POLY_STIPPLE, st_update_polygon_stipple)
 ST_STATE(ST_NEW_WINDOW_RECTANGLES, st_update_window_rectangles)
-ST_STATE(ST_NEW_BLEND, st_update_blend)
 ST_STATE(ST_NEW_BLEND_COLOR, st_update_blend_color)
 
 ST_STATE(ST_NEW_VS_SAMPLER_VIEWS, st_update_vertex_textures)
@@ -33,6 +32,7 @@ ST_STATE(ST_NEW_GS_IMAGES, st_bind_gs_images)
 ST_STATE(ST_NEW_FS_IMAGES, st_bind_fs_images)
 
 ST_STATE(ST_NEW_FB_STATE, st_update_framebuffer_state) /* depends on update_*_texture and bind_*_images */
+ST_STATE(ST_NEW_BLEND, st_update_blend) /* depends on update_framebuffer_state */
 ST_STATE(ST_NEW_RASTERIZER, st_update_rasterizer) /* depends on update_framebuffer_state */
 ST_STATE(ST_NEW_SAMPLE_MASK, st_update_sample_mask) /* depends on update_framebuffer_state */
 ST_STATE(ST_NEW_SAMPLE_SHADING, st_update_sample_shading)

src/mesa/state_tracker/st_context.h

@@ -164,6 +164,7 @@ struct st_context
       unsigned fb_height;
       unsigned fb_num_samples;
       unsigned fb_num_layers;
+      unsigned fb_num_cb;
       unsigned num_viewports;
       struct pipe_scissor_state scissor[PIPE_MAX_VIEWPORTS];
       struct pipe_viewport_state viewport[PIPE_MAX_VIEWPORTS];