[Mesa-dev] [PATCH] i965: Rewrite ir_tex to ir_txl with lod 0 for vertex shaders

[Kristian Høgsberg]

The ir_tex opcode turns into a sample or sample_c message, which will try to
compute derivatives to determine the lod. This produces garbage for
non-fragment shaders where the sample coordinates don't correspond to
subspans.

We fix this by rewriting the opcode from ir_tex to ir_txl and setting the
lod to 0.

https://bugs.freedesktop.org/show_bug.cgi?id=89457
Signed-off-by: Kristian Høgsberg <krh at bitplanet.net>
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 0049b2d..4e99366 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -1839,6 +1839,15 @@ fs_visitor::emit_texture_gen7(ir_texture_opcode op, fs_reg dst,
       offset_value.file != BAD_FILE && offset_value.file != IMM;
    bool coordinate_done = false;
 
+   /* The sampler can only meaningfully compute LOD for fragment shader
+    * messages. For all other stages, we change the opcode to ir_txl and
+    * hardcode the LOD to 0.
+    */
+   if (stage != MESA_SHADER_FRAGMENT && op == ir_tex) {
+      op = ir_txl;
+      lod = fs_reg(0.0f);
+   }
+
    /* Set up the LOD info */
    switch (op) {
    case ir_tex:
-- 
2.1.0