mesa: Use location VERT_ATTRIB_GENERIC0 for vertex attribute 0

In OpenGL 3.1 attribute 0 becomes non-magic, just like in
OpenGL ES 2.0. Earlier versions of OpenGL used attribute 0
exclusively for vertex position.

V2: Add a utility function _mesa_attr_zero_aliases_vertex() in
    varray.h

Fixes 4 Khronos OpenGL CTS failures:
glGetVertexAttrib
depth24_basic
depth24_precision
rgb8_rgba8_rgb

Cc: <[email protected]>
Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>

2 files changed, 17 insertions, 7 deletions

diff --git a/src/mesa/main/varray.c b/src/mesa/main/varray.c
index 66a3ef119af..81f71f8265e 100644
--- a/src/mesa/main/varray.c
+++ b/src/mesa/main/varray.c
@@ -784,13 +784,7 @@ static const GLfloat *
 get_current_attrib(struct gl_context *ctx, GLuint index, const char *function)
 {
    if (index == 0) {
-      /* In OpenGL 3.1 attribute 0 becomes non-magic, just like in OpenGL ES
-       * 2.0.  Note that we cannot just check for API_OPENGL_CORE here because
-       * that will erroneously allow this usage in a 3.0 forward-compatible
-       * context too.
-       */
-      if ((ctx->API != API_OPENGL_CORE || ctx->Version < 31)
-          && ctx->API != API_OPENGLES2) {
+      if (_mesa_attr_zero_aliases_vertex(ctx)) {
 	 _mesa_error(ctx, GL_INVALID_OPERATION, "%s(index==0)", function);
 	 return NULL;
       }
diff --git a/src/mesa/main/varray.h b/src/mesa/main/varray.h
index bc820ed2357..d10f78e64a3 100644
--- a/src/mesa/main/varray.h
+++ b/src/mesa/main/varray.h
@@ -106,6 +106,22 @@ _mesa_update_client_array(struct gl_context *ctx,
    _mesa_reference_buffer_object(ctx, &dst->BufferObj, binding->BufferObj);
 }
 
+static inline bool
+_mesa_attr_zero_aliases_vertex(struct gl_context *ctx)
+{
+   const bool is_forward_compatible_context =
+      ctx->Const.ContextFlags & GL_CONTEXT_FLAG_FORWARD_COMPATIBLE_BIT;
+
+   /* In OpenGL 3.1 attribute 0 becomes non-magic, just like in OpenGL ES
+    * 2.0.  Note that we cannot just check for API_OPENGL_COMPAT here because
+    * that will erroneously allow this usage in a 3.0 forward-compatible
+    * context too.
+    */
+   return (ctx->API == API_OPENGLES
+           || (ctx->API == API_OPENGL_COMPAT
+               && !is_forward_compatible_context));
+}
+
 extern void GLAPIENTRY
 _mesa_VertexPointer(GLint size, GLenum type, GLsizei stride,
                     const GLvoid *ptr);