i965/vec4: Initialize LOD to 0.0f for textureQueryLevels() and texture().

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.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index c39f97e3962aee511db9b2b464e6aa27232e0bc6..b8f90f2aa20c2b7cdf0e9054be1ef7fe224c6b50 100644 (file)
--- 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;