i965 Gen6: Implement gl_ClipVertex.

This patch implements proper support for gl_ClipVertex by causing the
new VS backend to populate the clip distance VUE slots using
VERT_RESULT_CLIP_VERTEX when appropriate, and by using the
untransformed clip planes in ctx->Transform.EyeUserPlane rather than
the transformed clip planes in ctx->Transform._ClipUserPlane when a
GLSL-based vertex shader is in use.

When not using a GLSL-based vertex shader, we use
ctx->Transform._ClipUserPlane (which is what we used prior to this
patch).  This ensures that clipping is still performed correctly for
fixed function and ARB vertex programs.  A new function,
brw_select_clip_planes() is used to determine whether to use
_ClipUserPlane or EyeUserPlane, so that the logic for making this
decision is shared between the new and old vertex shaders.

Fixes the following Piglit tests on i965 Gen6:
- vs-clip-vertex-const-accept
- vs-clip-vertex-const-reject
- vs-clip-vertex-different-from-position
- vs-clip-vertex-equal-to-position
- vs-clip-vertex-homogeneity
- vs-clip-based-on-position
- vs-clip-based-on-position-homogeneity
- clip-plane-transformation clipvert_pos
- clip-plane-transformation pos_clipvert
- clip-plane-transformation pos

Reviewed-by: Kenneth Graunke <[email protected]>
Reviewed-by: Chad Versace <[email protected]>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 71cbe0443d9..4fe442fa408 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -1493,13 +1493,20 @@ struct gl_texture_attrib
 
 
 /**
+ * Data structure representing a single clip plane (e.g. one of the elements
+ * of the ctx->Transform.EyeUserPlane or ctx->Transform._ClipUserPlane array).
+ */
+typedef GLfloat gl_clip_plane[4];
+
+
+/**
  * Transformation attribute group (GL_TRANSFORM_BIT).
  */
 struct gl_transform_attrib
 {
    GLenum MatrixMode;				/**< Matrix mode */
-   GLfloat EyeUserPlane[MAX_CLIP_PLANES][4];	/**< User clip planes */
-   GLfloat _ClipUserPlane[MAX_CLIP_PLANES][4];	/**< derived */
+   gl_clip_plane EyeUserPlane[MAX_CLIP_PLANES];	/**< User clip planes */
+   gl_clip_plane _ClipUserPlane[MAX_CLIP_PLANES]; /**< derived */
    GLbitfield ClipPlanesEnabled;                /**< on/off bitmask */
    GLboolean Normalize;				/**< Normalize all normals? */
    GLboolean RescaleNormals;			/**< GL_EXT_rescale_normal */