r300g: implement gl_FrontFacing

1 files changed, 43 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/r300/compiler/radeon_compiler.c b/src/mesa/drivers/dri/r300/compiler/radeon_compiler.c
index 1c8ba864a4..935dc9b0a8 100644
--- a/src/mesa/drivers/dri/r300/compiler/radeon_compiler.c
+++ b/src/mesa/drivers/dri/r300/compiler/radeon_compiler.c
@@ -307,3 +307,46 @@ void rc_transform_fragment_wpos(struct radeon_compiler * c, unsigned wpos, unsig
 	}
 }
 
+
+/**
+ * The FACE input in hardware contains 1 if it's a back face, 0 otherwise.
+ * Gallium and OpenGL define it the other way around.
+ *
+ * So let's just negate FACE at the beginning of the shader and rewrite the rest
+ * of the shader to read from the newly allocated temporary.
+ */
+void rc_transform_fragment_face(struct radeon_compiler *c, unsigned face)
+{
+	unsigned tempregi = rc_find_free_temporary(c);
+	struct rc_instruction *inst_add;
+	struct rc_instruction *inst;
+
+	/* perspective divide */
+	inst_add = rc_insert_new_instruction(c, &c->Program.Instructions);
+	inst_add->U.I.Opcode = RC_OPCODE_ADD;
+
+	inst_add->U.I.DstReg.File = RC_FILE_TEMPORARY;
+	inst_add->U.I.DstReg.Index = tempregi;
+	inst_add->U.I.DstReg.WriteMask = RC_MASK_X;
+
+	inst_add->U.I.SrcReg[0].File = RC_FILE_NONE;
+	inst_add->U.I.SrcReg[0].Swizzle = RC_SWIZZLE_1111;
+
+	inst_add->U.I.SrcReg[1].File = RC_FILE_INPUT;
+	inst_add->U.I.SrcReg[1].Index = face;
+	inst_add->U.I.SrcReg[1].Swizzle = RC_SWIZZLE_XXXX;
+	inst_add->U.I.SrcReg[1].Negate = RC_MASK_XYZW;
+
+	for (inst = inst_add->Next; inst != &c->Program.Instructions; inst = inst->Next) {
+		const struct rc_opcode_info * opcode = rc_get_opcode_info(inst->U.I.Opcode);
+		unsigned i;
+
+		for(i = 0; i < opcode->NumSrcRegs; i++) {
+			if (inst->U.I.SrcReg[i].File == RC_FILE_INPUT &&
+			    inst->U.I.SrcReg[i].Index == face) {
+				inst->U.I.SrcReg[i].File = RC_FILE_TEMPORARY;
+				inst->U.I.SrcReg[i].Index = tempregi;
+			}
+		}
+	}
+}