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src/gallium/drivers/r300/r300_vs_draw.c

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+/*
+ * Copyright 2009 Marek Olšák <[email protected]>
+ * Copyright 2026 Pavel Ondračka <[email protected]>
+ * SPDX-License-Identifier: MIT
+ */
+
+/* Vertex shader setup for the swtcl (draw-based) path.
+ *
+ * NIR transforms applied before handing to the draw module:
+ * 1) Secondary color output requires primary color — insert zero primary if absent.
+ * 2) Any back-face color requires all 4 color outputs — insert zeros for missing ones.
+ * 3) Append a generic output containing a copy of gl_Position, used as WPOS
+ *    by the hardware fragment shader.
+ */
+
+#include "r300_vs.h"
+
+#include "nir/nir.h"
+#include "nir/nir_builder.h"
+#include "compiler/nir_to_rc.h"
+#include "compiler/r300_nir.h"
+
+#include "draw/draw_context.h"
+
+static nir_variable *
+r300_draw_find_shader_out(nir_shader *nir, unsigned location)
+{
+    nir_foreach_shader_out_variable(var, nir) {
+        if (var->data.location == location)
+            return var;
+    }
+    return NULL;
+}
+
+/* Add a missing output variable and write zeros to it. */
+static void
+r300_draw_add_zero_output(nir_shader *nir, nir_builder *b, unsigned location,
+                          const char *name)
+{
+    nir_variable *var = nir_variable_create(nir, nir_var_shader_out,
+                                            glsl_vec4_type(), name);
+    var->data.location = location;
+    var->data.interpolation = INTERP_MODE_NOPERSPECTIVE;
+    nir_store_var(b, var, nir_imm_zero(b, 4, 32), 0xf);
+}
+
+/* Ensure that the color output layout satisfies the r300 hardware rules:
+ *   - COL1 (secondary front color) requires COL0
+ *   - Any back-face color requires all four color outputs (COL0/COL1/BFC0/BFC1) */
+static bool
+r300_nir_add_missing_color_outputs(nir_shader *nir)
+{
+    bool color_used[2] = {false, false};
+    bool bcolor_used[2] = {false, false};
+
+    nir_foreach_shader_out_variable(var, nir) {
+        switch (var->data.location) {
+        case VARYING_SLOT_COL0: color_used[0] = true; break;
+        case VARYING_SLOT_COL1: color_used[1] = true; break;
+        case VARYING_SLOT_BFC0: bcolor_used[0] = true; break;
+        case VARYING_SLOT_BFC1: bcolor_used[1] = true; break;
+        default: break;
+        }
+    }
+
+    nir_function_impl *impl = nir_shader_get_entrypoint(nir);
+    nir_builder b = nir_builder_create(impl);
+    b.cursor = nir_after_impl(impl);
+    bool progress = false;
+
+    if (color_used[1] && !color_used[0]) {
+        r300_draw_add_zero_output(nir, &b, VARYING_SLOT_COL0, "gl_FrontColor");
+        color_used[0] = true;
+        progress = true;
+    }
+
+    if (bcolor_used[0] || bcolor_used[1]) {
+        if (!color_used[0]) {
+            r300_draw_add_zero_output(nir, &b, VARYING_SLOT_COL0, "gl_FrontColor");
+            progress = true;
+        }
+        if (!color_used[1]) {
+            r300_draw_add_zero_output(nir, &b, VARYING_SLOT_COL1, "gl_FrontSecondaryColor");
+            progress = true;
+        }
+        if (!bcolor_used[0]) {
+            r300_draw_add_zero_output(nir, &b, VARYING_SLOT_BFC0, "gl_BackColor");
+            progress = true;
+        }
+        if (!bcolor_used[1]) {
+            r300_draw_add_zero_output(nir, &b, VARYING_SLOT_BFC1, "gl_BackSecondaryColor");
+            progress = true;
+        }
+    }
+
+    return nir_progress(progress, impl, nir_metadata_control_flow);
+}
+
+/* Assign driver_location to the variable at the given slot (if present)
+ * and update the outputs field. */
+static void
+r300_draw_assign_output(nir_shader *nir, unsigned location, int *field,
+                        unsigned *driver_location)
+{
+    nir_variable *var = r300_draw_find_shader_out(nir, location);
+    if (!var)
+        return;
+    *field = *driver_location;
+    var->data.driver_location = (*driver_location)++;
+}
+
+/* Build vs->outputs from the (transformed) NIR and assign driver_locations.
+ * The WPOS output is identified by wpos_var and placed last. */
+static void
+r300_draw_fill_vs_outputs(nir_shader *nir, nir_variable *wpos_var,
+                          struct r300_vertex_shader_code *vs)
+{
+    struct r300_shader_semantics *outputs = &vs->outputs;
+    unsigned driver_location = 0;
+
+    r300_shader_semantics_reset(outputs);
+
+    r300_draw_assign_output(nir, VARYING_SLOT_POS, &outputs->pos, &driver_location);
+    r300_draw_assign_output(nir, VARYING_SLOT_PSIZ, &outputs->psize, &driver_location);
+    r300_draw_assign_output(nir, VARYING_SLOT_COL0, &outputs->color[0], &driver_location);
+    r300_draw_assign_output(nir, VARYING_SLOT_COL1, &outputs->color[1], &driver_location);
+    r300_draw_assign_output(nir, VARYING_SLOT_BFC0, &outputs->bcolor[0], &driver_location);
+    r300_draw_assign_output(nir, VARYING_SLOT_BFC1, &outputs->bcolor[1], &driver_location);
+
+    for (unsigned g = 0; g < ATTR_GENERIC_COUNT; g++) {
+        unsigned loc = VARYING_SLOT_VAR0 + g;
+        nir_variable *var = r300_draw_find_shader_out(nir, loc);
+        if (!var || var == wpos_var)
+            continue;
+        outputs->generic[g] = driver_location;
+        outputs->num_generic++;
+        var->data.driver_location = driver_location++;
+    }
+
+    r300_draw_assign_output(nir, VARYING_SLOT_FOGC, &outputs->fog, &driver_location);
+
+    /* Draw still needs these non-rasterized outputs in its shader info. */
+    nir_variable *edge_var = r300_draw_find_shader_out(nir, VARYING_SLOT_EDGE);
+    if (edge_var)
+        edge_var->data.driver_location = driver_location++;
+    nir_variable *clip_vertex_var =
+        r300_draw_find_shader_out(nir, VARYING_SLOT_CLIP_VERTEX);
+    if (clip_vertex_var)
+        clip_vertex_var->data.driver_location = driver_location++;
+
+    if (wpos_var) {
+        outputs->wpos = driver_location;
+        wpos_var->data.driver_location = driver_location;
+    }
+}
+
+void
+r300_draw_init_vertex_shader(struct r300_context *r300,
+                             struct r300_vertex_shader *vs)
+{
+    /* Clone the NIR and apply the +9 varying shift to align VS outputs with
+     * FS inputs (which get the same shift in nir_to_rc). */
+    nir_shader *nir = nir_shader_clone(NULL, vs->state.ir.nir);
+    ntr_fixup_varying_slots(nir, nir_var_shader_out);
+
+    NIR_PASS(_, nir, r300_nir_add_missing_color_outputs);
+    nir_variable *wpos_var = NULL;
+    NIR_PASS(_, nir, r300_nir_add_wpos, &wpos_var);
+
+    /* Fill in the r300 rasterizer outputs and assign driver locations. */
+    r300_draw_fill_vs_outputs(nir, wpos_var, vs->shader);
+
+    /* Hand the transformed NIR off to the draw module. */
+    struct pipe_shader_state new_vs = {
+        .type = PIPE_SHADER_IR_NIR,
+        .ir.nir = nir,
+    };
+    vs->draw_vs = draw_create_vertex_shader(r300->draw, &new_vs);
+}