[Mesa-dev] [PATCH 1/2] i965/fs: Fix texelFetchOffset()

[Eric Anholt]

It appears that when using 'ld' with the offset bits, address bounds
checking happens before the offset is applied, so parts of the drawing
in piglit texelFetchOffset() with a negative texcoord go black.
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |   27 ++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 51c1fd2..1ef3fb3 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -990,8 +990,9 @@ fs_visitor::emit_texture_gen7(ir_texture *ir, fs_reg dst, fs_reg coordinate,
    int base_mrf = 2;
    int reg_width = c->dispatch_width / 8;
    bool header_present = false;
+   int offsets[3];
 
-   if (ir->offset) {
+   if (ir->offset && ir->op != ir_txf) {
       /* The offsets set up by the ir_texture visitor are in the
        * m1 header, so we can't go headerless.
        */
@@ -1054,9 +1055,23 @@ fs_visitor::emit_texture_gen7(ir_texture *ir, fs_reg dst, fs_reg coordinate,
       mlen += reg_width;
       break;
    case ir_txf:
+      /* It appears that the ld instruction used for txf does its
+       * address bounds check before adding in the offset.  To work
+       * around this, just add the integer offset to the integer texel
+       * coordinate, and don't put the offset in the header.
+       */
+      if (ir->offset) {
+	 ir_constant *offset = ir->offset->as_constant();
+	 offsets[0] = offset->value.i[0];
+	 offsets[1] = offset->value.i[1];
+	 offsets[2] = offset->value.i[2];
+      } else {
+	 memset(offsets, 0, sizeof(offsets));
+      }
+
       /* Unfortunately, the parameters for LD are intermixed: u, lod, v, r. */
-      emit(BRW_OPCODE_MOV,
-	   fs_reg(MRF, base_mrf + mlen, BRW_REGISTER_TYPE_D), coordinate);
+      emit(BRW_OPCODE_ADD,
+	   fs_reg(MRF, base_mrf + mlen, BRW_REGISTER_TYPE_D), coordinate, offsets[0]);
       coordinate.reg_offset++;
       mlen += reg_width;
 
@@ -1065,8 +1080,8 @@ fs_visitor::emit_texture_gen7(ir_texture *ir, fs_reg dst, fs_reg coordinate,
       mlen += reg_width;
 
       for (int i = 1; i < ir->coordinate->type->vector_elements; i++) {
-	 emit(BRW_OPCODE_MOV,
-	      fs_reg(MRF, base_mrf + mlen, BRW_REGISTER_TYPE_D), coordinate);
+	 emit(BRW_OPCODE_ADD,
+	      fs_reg(MRF, base_mrf + mlen, BRW_REGISTER_TYPE_D), coordinate, offsets[i]);
 	 coordinate.reg_offset++;
 	 mlen += reg_width;
       }
@@ -1128,7 +1143,7 @@ fs_visitor::visit(ir_texture *ir)
       ir->coordinate->accept(this);
    fs_reg coordinate = this->result;
 
-   if (ir->offset != NULL) {
+   if (ir->offset != NULL && !(intel->gen == 7 && ir->op == ir_txf)) {
       uint32_t offset_bits = brw_texture_offset(ir->offset->as_constant());
 
       /* Explicitly set up the message header by copying g0 to msg reg m1. */
-- 
1.7.10