Plan stroke preview composite sequence

src/paint_renderer/compositor.cpp

@@ -1264,6 +1264,52 @@ CanvasStrokeMaterialPlan plan_canvas_stroke_material(CanvasStrokeMaterialRequest
     return plan;
 }
 
+StrokePreviewCompositePlan plan_stroke_preview_composite(StrokePreviewCompositeRequest request) noexcept
+{
+    StrokePreviewCompositePlan plan;
+    plan.uses_mixer = request.uses_mixer;
+    plan.uses_dual = request.uses_dual;
+    plan.uses_pattern = request.uses_pattern;
+
+    auto append_step = [&plan](StrokePreviewCompositeStep step) noexcept {
+        if (plan.step_count >= plan.steps.size()) {
+            return;
+        }
+        plan.steps[plan.step_count] = step;
+        ++plan.step_count;
+    };
+    auto bind = [&plan](StrokePreviewTextureRole role, std::uint8_t slot) noexcept {
+        if (plan.texture_slot_count >= plan.texture_slots.size()) {
+            return;
+        }
+        plan.texture_slots[plan.texture_slot_count] = StrokePreviewTextureSlotPlan {
+            .role = role,
+            .slot = slot,
+        };
+        ++plan.texture_slot_count;
+    };
+
+    append_step(StrokePreviewCompositeStep::checkerboard_background);
+    append_step(StrokePreviewCompositeStep::capture_background_texture);
+    append_step(StrokePreviewCompositeStep::bind_final_composite_inputs);
+    append_step(StrokePreviewCompositeStep::final_composite_draw);
+    append_step(StrokePreviewCompositeStep::copy_preview_texture);
+
+    bind(StrokePreviewTextureRole::background, 0);
+    bind(StrokePreviewTextureRole::stroke, 1);
+    if (request.uses_dual) {
+        bind(StrokePreviewTextureRole::dual, 3);
+    }
+    if (request.uses_pattern) {
+        bind(StrokePreviewTextureRole::pattern, 4);
+    }
+    if (request.uses_mixer) {
+        bind(StrokePreviewTextureRole::mixer, 3);
+    }
+
+    return plan;
+}
+
 pp::foundation::Result<CanvasBlendGatePlan> plan_canvas_blend_gate(
     pp::renderer::RenderDeviceFeatures features,
     CanvasBlendGateRequest request) noexcept