softpipe: try and use back color for a slot if color fails.

In the case where a front and back output are specified, the draw code will
copy the back output into the front color slot and everything is happy.

However if no front is specified then the draw code will do a bad copy (separate patch), but also the frag shader won't pick up the color as there there is
no write to COLOR from the vertex shader just BCOLOR.

This patch fixes that problem so if it can't find a vertex shader output
for the front color slot, it will go and lookup and use one for the back color
slot.

Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/src/gallium/drivers/softpipe/sp_state_derived.c b/src/gallium/drivers/softpipe/sp_state_derived.c
index f89d23c..5685997 100644 (file)
--- a/src/gallium/drivers/softpipe/sp_state_derived.c
+++ b/src/gallium/drivers/softpipe/sp_state_derived.c
@@ -121,6 +121,11 @@ softpipe_get_vertex_info(struct softpipe_context *softpipe)
          src = draw_find_shader_output(softpipe->draw,
                                        fsInfo->input_semantic_name[i],
                                        fsInfo->input_semantic_index[i]);
+        if (fsInfo->input_semantic_name[i] == TGSI_SEMANTIC_COLOR && src == 0)
+          /* try and find a bcolor */
+          src = draw_find_shader_output(softpipe->draw,
+                                        TGSI_SEMANTIC_BCOLOR, fsInfo->input_semantic_index[i]);
+
          draw_emit_vertex_attr(vinfo, EMIT_4F, interp, src);
       }