diff options
| -rw-r--r-- | src/mesa/drivers/dri/i965/brw_fs.cpp | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp index 053c4c32719..20485aa4036 100644 --- a/src/mesa/drivers/dri/i965/brw_fs.cpp +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp @@ -1205,12 +1205,23 @@ fs_visitor::emit_frontfacing_interpolation(ir_variable *ir) emit(ASR(*reg, g0, fs_reg(15))); } else { - struct brw_reg r1_6ud = retype(brw_vec1_grf(1, 6), BRW_REGISTER_TYPE_UD); - /* bit 31 is "primitive is back face", so checking < (1 << 31) gives - * us front face + /* Bit 31 of g1.6 is 0 if the polygon is front facing. We want to create + * a boolean result from this (1/true or 0/false). + * + * Like in the above case, since the bit is the MSB of g1.6:UD we can use + * the negation source modifier to flip it. Unfortunately the SHR + * instruction only operates on UD (or D with an abs source modifier) + * sources without negation. + * + * Instead, use ASR (which will give ~0/true or 0/false) followed by an + * AND 1. */ - emit(CMP(*reg, fs_reg(r1_6ud), fs_reg(1u << 31), BRW_CONDITIONAL_L)); - emit(BRW_OPCODE_AND, *reg, *reg, fs_reg(1u)); + fs_reg asr = fs_reg(this, ir->type); + fs_reg g1_6 = fs_reg(retype(brw_vec1_grf(1, 6), BRW_REGISTER_TYPE_D)); + g1_6.negate = true; + + emit(ASR(asr, g1_6, fs_reg(31))); + emit(AND(*reg, asr, fs_reg(1))); } return reg; |