mesa: fix GLSL issue preventing use of all 16 generic vertex attributes

Only 15 actually worked before since we always reserved generic[0] as an
alias for vertex position.

The case of vertex attribute 0 is tricky.  The spec says that there is no
aliasing between generic vertex attributes 0..MAX_VERTEX_ATTRIBS-1 and the
conventional attributes.  But it also says that calls to glVertexAttrib(0, v)
are equivalent to glVertex(v).  The distinction seems to be in glVertex-mode
versus vertex array mode.

So update the VBO code so that if the shader uses generic[0] but not gl_Vertex,
route the attribute data set with glVertex() to go to shader input generic[0].

No change needed for the glDrawArrays/Elements() path.

This is a potentially risky change so regressions are possible.  All the usual
tests seem OK though.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mesa/vbo/vbo_exec_api.c b/src/mesa/vbo/vbo_exec_api.c
index d48f5230cb..f6daa253fd 100644
--- a/src/mesa/vbo/vbo_exec_api.c
+++ b/src/mesa/vbo/vbo_exec_api.c
@@ -148,11 +148,14 @@ static void vbo_exec_copy_to_current( struct vbo_exec_context *exec )
          /* Note: the exec->vtx.current[i] pointers point into the
           * ctx->Current.Attrib and ctx->Light.Material.Attrib arrays.
           */
+         if (exec->vtx.attrptr[i]) {
+
 	 COPY_CLEAN_4V(current, 
 		       exec->vtx.attrsz[i], 
 		       exec->vtx.attrptr[i]);
 
-	 
+	 }
+
 	 /* Given that we explicitly state size here, there is no need
 	  * for the COPY_CLEAN above, could just copy 16 bytes and be
 	  * done.  The only problem is when Mesa accesses ctx->Current