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

src/paint_renderer/compositor.h

@@ -109,6 +109,44 @@ struct CanvasStrokeMaterialPlan {
     std::size_t texture_binding_count = 0;
 };
 
+enum class StrokePreviewCompositeStep : std::uint8_t {
+    checkerboard_background,
+    capture_background_texture,
+    bind_final_composite_inputs,
+    final_composite_draw,
+    copy_preview_texture,
+};
+
+enum class StrokePreviewTextureRole : std::uint8_t {
+    background,
+    stroke,
+    mask,
+    dual,
+    pattern,
+    mixer,
+};
+
+struct StrokePreviewTextureSlotPlan {
+    StrokePreviewTextureRole role = StrokePreviewTextureRole::background;
+    std::uint8_t slot = 0;
+};
+
+struct StrokePreviewCompositeRequest {
+    bool uses_mixer = false;
+    bool uses_dual = false;
+    bool uses_pattern = false;
+};
+
+struct StrokePreviewCompositePlan {
+    std::array<StrokePreviewCompositeStep, 5> steps {};
+    std::size_t step_count = 0;
+    std::array<StrokePreviewTextureSlotPlan, 5> texture_slots {};
+    std::size_t texture_slot_count = 0;
+    bool uses_mixer = false;
+    bool uses_dual = false;
+    bool uses_pattern = false;
+};
+
 struct CanvasBlendGateRequest {
     pp::renderer::Extent2D extent {};
     std::span<const int> layer_blend_modes;
@@ -440,6 +478,9 @@ export_document_animation_frames_equirectangular_pngs(
 [[nodiscard]] CanvasStrokeMaterialPlan plan_canvas_stroke_material(
     CanvasStrokeMaterialRequest request) noexcept;
 
+[[nodiscard]] StrokePreviewCompositePlan plan_stroke_preview_composite(
+    StrokePreviewCompositeRequest request) noexcept;
+
 [[nodiscard]] pp::foundation::Result<CanvasBlendGatePlan> plan_canvas_blend_gate(
     pp::renderer::RenderDeviceFeatures features,
     CanvasBlendGateRequest request) noexcept;