mesa: create/use a fallback texture when bound texture is incomplete

When a GLSL sampler reads from an incomplete texture it should
return (0,0,0,1).  Instead of jumping through hoops in all the drivers
to make this happen, just create/install a fallback texture with those
texel values.

Fixes piglit/fp-incomplete-tex on i965 and more importantly, fixes some
GPU lockups when trying to sample from missing surfaces.  If a binding
table entry is NULL, it seems that sampling sometimes works, but not
always (lockup).

Todo: create a fallback texture for each type of texture target?

1 files changed, 7 insertions, 2 deletions

diff --git a/src/mesa/main/texstate.c b/src/mesa/main/texstate.c
index 73f8a5339ec..32d55ba8d58 100644
--- a/src/mesa/main/texstate.c
+++ b/src/mesa/main/texstate.c
@@ -561,8 +561,13 @@ update_texture_state( GLcontext *ctx )
       }
 
       if (!texUnit->_ReallyEnabled) {
-         _mesa_reference_texobj(&texUnit->_Current, NULL);
-         continue;
+         /* If we get here it means the shader (or fixed-function state)
+          * is expecting a texture object, but there isn't one (or it's
+          * incomplete).  Use the fallback texture.
+          */
+         struct gl_texture_object *texObj = _mesa_get_fallback_texture(ctx);
+         texUnit->_ReallyEnabled = 1 << TEXTURE_2D_INDEX;
+         _mesa_reference_texobj(&texUnit->_Current, texObj);
       }
 
       /* if we get here, we know this texture unit is enabled */