Extract stroke dual pass boundary

src/legacy_canvas_stroke_execution_services.h

@@ -179,9 +179,42 @@ struct LegacyCanvasStrokeMixPassResult {
     std::size_t composed_planes = 0;
 };
 
+struct LegacyCanvasStrokeDualPassRequest {
+    std::string_view context;
+    std::span<const LegacyCanvasStrokeMixPassPlane> planes;
+    std::function<void()> bind_brush_tip;
+    std::function<void()> unbind_brush_tip;
+    std::function<void()> setup_dual_shader;
+    std::function<void()> execute_frame_pass;
+};
+
+struct LegacyCanvasStrokeDualPassResult {
+    bool ok = false;
+    std::size_t composed_planes = 0;
+};
+
 [[nodiscard]] inline LegacyCanvasStrokeMixPassResult execute_legacy_canvas_stroke_mix_pass(
     const LegacyCanvasStrokeMixPassRequest& request);
 
+[[nodiscard]] inline LegacyCanvasStrokeDualPassResult execute_legacy_canvas_stroke_dual_pass(
+    const LegacyCanvasStrokeDualPassRequest& request)
+{
+    LegacyCanvasStrokeDualPassResult result;
+    if (!request.setup_dual_shader ||
+        !request.bind_brush_tip ||
+        !request.unbind_brush_tip ||
+        !request.execute_frame_pass) {
+        return result;
+    }
+
+    request.setup_dual_shader();
+    request.bind_brush_tip();
+    request.execute_frame_pass();
+    request.unbind_brush_tip();
+    result.ok = true;
+    return result;
+}
+
 template <std::size_t PlaneCount, typename HasTarget>
 [[nodiscard]] inline std::array<LegacyCanvasStrokeMixPassPlane, PlaneCount>
 plan_legacy_canvas_stroke_mix_pass_planes(