--- /dev/null
+/*
+ * Copyright © 2015 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ * Rob Clark <robclark@freedesktop.org>
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+#define MAX_COLORS 2 /* VARYING_SLOT_COL0/COL1 */
+
+typedef struct {
+ nir_builder b;
+ nir_shader *shader;
+ nir_variable *face;
+ struct {
+ nir_variable *front; /* COLn */
+ nir_variable *back; /* BFCn */
+ } colors[MAX_COLORS];
+ int colors_count;
+} lower_2side_state;
+
+
+/* Lowering pass for fragment shaders to emulated two-sided-color. For
+ * each COLOR input, a corresponding BCOLOR input is created, and bcsel
+ * instruction used to select front or back color based on FACE.
+ */
+
+static nir_variable *
+create_input(nir_shader *shader, unsigned drvloc, gl_varying_slot slot)
+{
+ nir_variable *var = rzalloc(shader, nir_variable);
+
+ var->data.driver_location = drvloc;
+ var->type = glsl_vec4_type();
+ var->data.mode = nir_var_shader_in;
+ var->name = ralloc_asprintf(var, "in_%d", drvloc);
+ var->data.index = 0;
+ var->data.location = slot;
+
+ exec_list_push_tail(&shader->inputs, &var->node);
+
+ return var;
+}
+
+static nir_ssa_def *
+load_input(nir_builder *b, nir_variable *in)
+{
+ nir_intrinsic_instr *load;
+
+ load = nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_input);
+ load->num_components = 4;
+ load->const_index[0] = in->data.driver_location;
+ nir_ssa_dest_init(&load->instr, &load->dest, 4, NULL);
+ nir_builder_instr_insert(b, &load->instr);
+
+ return &load->dest.ssa;
+}
+
+static int
+setup_inputs(lower_2side_state *state)
+{
+ int maxloc = -1;
+
+ /* find color/face inputs: */
+ foreach_list_typed(nir_variable, var, node, &state->shader->inputs) {
+ int loc = var->data.driver_location;
+
+ /* keep track of last used driver-location.. we'll be
+ * appending BCLr/FACE after last existing input:
+ */
+ maxloc = MAX2(maxloc, loc);
+
+ switch (var->data.location) {
+ case VARYING_SLOT_COL0:
+ case VARYING_SLOT_COL1:
+ assert(state->colors_count < ARRAY_SIZE(state->colors));
+ state->colors[state->colors_count].front = var;
+ state->colors_count++;
+ break;
+ case VARYING_SLOT_FACE:
+ state->face = var;
+ break;
+ }
+ }
+
+ /* if we don't have any color inputs, nothing to do: */
+ if (state->colors_count == 0)
+ return -1;
+
+ /* if we don't already have one, insert a FACE input: */
+ if (!state->face) {
+ state->face = create_input(state->shader, ++maxloc, VARYING_SLOT_FACE);
+ state->face->data.interpolation = INTERP_QUALIFIER_FLAT;
+ }
+
+ /* add required back-face color inputs: */
+ for (int i = 0; i < state->colors_count; i++) {
+ gl_varying_slot slot;
+
+ if (state->colors[i].front->data.location == VARYING_SLOT_COL0)
+ slot = VARYING_SLOT_BFC0;
+ else
+ slot = VARYING_SLOT_BFC1;
+
+ state->colors[i].back = create_input(state->shader, ++maxloc, slot);
+ }
+
+ return 0;
+}
+
+static bool
+nir_lower_two_sided_color_block(nir_block *block, void *void_state)
+{
+ lower_2side_state *state = void_state;
+ nir_builder *b = &state->b;
+
+ nir_foreach_instr_safe(block, instr) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+ if (intr->intrinsic != nir_intrinsic_load_input)
+ continue;
+
+ int idx;
+ for (idx = 0; idx < state->colors_count; idx++) {
+ unsigned drvloc =
+ state->colors[idx].front->data.driver_location;
+ if (intr->const_index[0] == drvloc) {
+ break;
+ }
+ }
+
+ if (idx == state->colors_count)
+ continue;
+
+ /* replace load_input(COLn) with
+ * bcsel(load_input(FACE), load_input(COLn), load_input(BFCn))
+ */
+ b->cursor = nir_before_instr(&intr->instr);
+ nir_ssa_def *face = nir_channel(b, load_input(b, state->face), 0);
+ nir_ssa_def *front = load_input(b, state->colors[idx].front);
+ nir_ssa_def *back = load_input(b, state->colors[idx].back);
+ nir_ssa_def *cond = nir_flt(b, face, nir_imm_float(b, 0.0));
+ nir_ssa_def *color = nir_bcsel(b, cond, back, front);
+
+ assert(intr->dest.is_ssa);
+ nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(color));
+ }
+
+ return true;
+}
+
+static void
+nir_lower_two_sided_color_impl(nir_function_impl *impl,
+ lower_2side_state *state)
+{
+ nir_builder *b = &state->b;
+
+ nir_builder_init(b, impl);
+
+ nir_foreach_block(impl, nir_lower_two_sided_color_block, state);
+
+ nir_metadata_preserve(impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+}
+
+void
+nir_lower_two_sided_color(nir_shader *shader)
+{
+ lower_2side_state state = {
+ .shader = shader,
+ };
+
+ if (shader->stage != MESA_SHADER_FRAGMENT)
+ return;
+
+ if (setup_inputs(&state) != 0)
+ return;
+
+ nir_foreach_overload(shader, overload) {
+ if (overload->impl)
+ nir_lower_two_sided_color_impl(overload->impl, &state);
+ }
+
+}
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