ir_constant_expression: Add support for the "faceforward" builtin.
diff --git a/src/glsl/ir_constant_expression.cpp b/src/glsl/ir_constant_expression.cpp
index 580ef1d..c939690 100644
--- a/src/glsl/ir_constant_expression.cpp
+++ b/src/glsl/ir_constant_expression.cpp
@@ -881,7 +881,10 @@
} else if (strcmp(callee, "exp2") == 0) {
expr = new(mem_ctx) ir_expression(ir_unop_exp2, type, op[0], NULL);
} else if (strcmp(callee, "faceforward") == 0) {
- return NULL; /* FINISHME: implement this */
+ if (dot(op[2], op[1]) < 0)
+ return op[0];
+ for (unsigned c = 0; c < op[0]->type->components(); c++)
+ data.f[c] = -op[0]->value.f[c];
} else if (strcmp(callee, "floor") == 0) {
expr = new(mem_ctx) ir_expression(ir_unop_floor, type, op[0], NULL);
} else if (strcmp(callee, "fract") == 0) {