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.

src/mesa/shader/slang/slang_link.c

@@ -318,7 +318,7 @@ _slang_resolve_attributes(struct gl_shader_program *shProg,
 {
    GLint attribMap[MAX_VERTEX_ATTRIBS];
    GLuint i, j;
-   GLbitfield usedAttributes;
+   GLbitfield usedAttributes; /* generics only, not legacy attributes */
 
    assert(origProg != linkedProg);
    assert(origProg->Target == GL_VERTEX_PROGRAM_ARB);
@@ -342,6 +342,15 @@ _slang_resolve_attributes(struct gl_shader_program *shProg,
       usedAttributes |= (1 << attr);
    }
 
+   /* If gl_Vertex is used, that actually counts against the limit
+    * on generic vertex attributes.  This avoids the ambiguity of
+    * whether glVertexAttrib4fv(0, v) sets legacy attribute 0 (vert pos)
+    * or generic attribute[0].  If gl_Vertex is used, we want the former.
+    */
+   if (origProg->InputsRead & VERT_BIT_POS) {
+      usedAttributes |= 0x1;
+   }
+
    /* initialize the generic attribute map entries to -1 */
    for (i = 0; i < MAX_VERTEX_ATTRIBS; i++) {
       attribMap[i] = -1;
@@ -384,7 +393,7 @@ _slang_resolve_attributes(struct gl_shader_program *shProg,
                    * Start at 1 since generic attribute 0 always aliases
                    * glVertex/position.
                    */
-                  for (attr = 1; attr < MAX_VERTEX_ATTRIBS; attr++) {
+                  for (attr = 0; attr < MAX_VERTEX_ATTRIBS; attr++) {
                      if (((1 << attr) & usedAttributes) == 0)
                         break;
                   }

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

src/mesa/vbo/vbo_exec_draw.c

@@ -175,7 +175,20 @@ static void vbo_exec_bind_arrays( GLcontext *ctx )
          exec->vtx.inputs[attr + 16] = &vbo->generic_currval[attr];
       }
       map = vbo->map_vp_arb;
+
+      /* check if VERT_ATTRIB_POS is not read but VERT_BIT_GENERIC0 is read.
+       * In that case we effectively need to route the data from
+       * glVertexAttrib(0, val) calls to feed into the GENERIC0 input.
+       */
+      if ((ctx->VertexProgram._Current->Base.InputsRead & VERT_BIT_POS) == 0 &&
+          (ctx->VertexProgram._Current->Base.InputsRead & VERT_BIT_GENERIC0)) {
+         exec->vtx.inputs[16] = exec->vtx.inputs[0];
+         exec->vtx.attrsz[16] = exec->vtx.attrsz[0];
+         exec->vtx.attrsz[0] = 0;
+      }
       break;
+   default:
+      assert(0);
    }
 
    /* Make all active attributes (including edgeflag) available as

src/mesa/vbo/vbo_save_draw.c

@@ -110,6 +110,9 @@ static void vbo_bind_vertex_list( GLcontext *ctx,
    GLuint data = node->buffer_offset;
    const GLuint *map;
    GLuint attr;
+   GLubyte node_attrsz[VBO_ATTRIB_MAX];  /* copy of node->attrsz[] */
+
+   memcpy(node_attrsz, node->attrsz, sizeof(node->attrsz));
 
    /* Install the default (ie Current) attributes first, then overlay
     * all active ones.
@@ -135,13 +138,26 @@ static void vbo_bind_vertex_list( GLcontext *ctx,
          save->inputs[attr + 16] = &vbo->generic_currval[attr];
       }
       map = vbo->map_vp_arb;
+
+      /* check if VERT_ATTRIB_POS is not read but VERT_BIT_GENERIC0 is read.
+       * In that case we effectively need to route the data from
+       * glVertexAttrib(0, val) calls to feed into the GENERIC0 input.
+       */
+      if ((ctx->VertexProgram._Current->Base.InputsRead & VERT_BIT_POS) == 0 &&
+          (ctx->VertexProgram._Current->Base.InputsRead & VERT_BIT_GENERIC0)) {
+         save->inputs[16] = save->inputs[0];
+         node_attrsz[16] = node_attrsz[0];
+         node_attrsz[0] = 0;
+      }
       break;
+   default:
+      assert(0);
    }
 
    for (attr = 0; attr < VERT_ATTRIB_MAX; attr++) {
       GLuint src = map[attr];
 
-      if (node->attrsz[src]) {
+      if (node_attrsz[src]) {
          /* override the default array set above */
          save->inputs[attr] = &arrays[attr];