Extract stroke mix setup shell

src/canvas.cpp

@@ -403,9 +403,8 @@ void Canvas::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2& bb_sz)
             return current_layer.face(plane_index);
         });
     const auto& b = m_current_stroke->m_brush;
-    [[maybe_unused]] const auto mix_result =
-        pp::panopainter::execute_legacy_canvas_stroke_mix_pass_with_setup(
-            [&] {
+    const auto mix_setup = pp::panopainter::make_legacy_canvas_stroke_mix_pass_setup(
+        [&] {
                 m_mixer.bindFramebuffer();
                 apply_canvas_viewport(0, 0, m_mixer.getWidth(), m_mixer.getHeight());
                 apply_canvas_capability(depth_test_state(), false);
@@ -417,9 +416,13 @@ void Canvas::stroke_draw_mix(const glm::vec2& bb_min, const glm::vec2& bb_sz)
                     static_cast<std::int32_t>(bb_sz.x),
                     static_cast<std::int32_t>(bb_sz.y));
             },
-            [&] {
+        [&] {
                 m_mixer.unbindFramebuffer();
-            },
+            });
+    [[maybe_unused]] const auto mix_result =
+        pp::panopainter::execute_legacy_canvas_stroke_mix_pass_with_setup(
+            mix_setup.begin,
+            mix_setup.end,
         pp::panopainter::make_legacy_canvas_stroke_mix_pass_request(
             "Canvas::stroke_draw_mix",
             m_size,

src/legacy_canvas_stroke_execution_services.h

@@ -340,6 +340,21 @@ struct LegacyCanvasStrokeMixPassResult {
     std::size_t composed_planes = 0;
 };
 
+struct LegacyCanvasStrokeMixPassSetup {
+    std::function<void()> begin;
+    std::function<void()> end;
+};
+
+[[nodiscard]] inline LegacyCanvasStrokeMixPassSetup make_legacy_canvas_stroke_mix_pass_setup(
+    std::function<void()> begin,
+    std::function<void()> end)
+{
+    return LegacyCanvasStrokeMixPassSetup {
+        .begin = std::move(begin),
+        .end = std::move(end),
+    };
+}
+
 [[nodiscard]] inline LegacyCanvasStrokeMixPassRequest make_legacy_canvas_stroke_mix_pass_request(
     std::string_view context,
     glm::vec2 resolution,