We implement textureQueryLevels (which takes no arguments, save the
sampler) using the resinfo message (which takes an argument of LOD).
Without initializing it, we'd generate a MOV from the null register to
load the LOD argument.
Essentially the same logic applies to texture. A vertex shader cannot
compute derivatives and so cannot produce an LOD, so TXL with an LOD of
0.0 is used.
---
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index c39f97e..b8f90f2 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -882,6 +882,18 @@ vec4_visitor::emit_texture(ir_texture_opcode op,
uint32_t sampler,
src_reg sampler_reg)
{
+ /* The sampler can only meaningfully compute LOD for fragment shader
+ * messages. For all other stages, we change the opcode to TXL and hardcode
+ * the LOD to 0.
+ *
+ * textureQueryLevels() is implemented in terms of TXS so we need to pass a
+ * valid LOD argument.
+ */
+ if (op == ir_tex || op == ir_query_levels) {
+ assert(lod.file == BAD_FILE);
+ lod = src_reg(0.0f);
+ }
+
enum opcode opcode;
switch (op) {
case ir_tex: opcode = SHADER_OPCODE_TXL; break;
--
2.4.9
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