Narrow retained canvas stroke execution helpers

src/legacy_canvas_stroke_execution_services.h

@@ -64,6 +64,24 @@ struct LegacyCanvasStrokePadRegionResult {
     std::array<pp::paint_renderer::CanvasStrokePoint, 6> ndc_quad {};
 };
 
+struct LegacyCanvasStrokePadFace {
+    int index = 0;
+    bool dirty = false;
+    glm::vec4 pass_dirty_box {};
+};
+
+struct LegacyCanvasStrokePadExecutionRequest {
+    std::string_view context;
+    pp::renderer::Extent2D extent {};
+    std::span<const LegacyCanvasStrokePadFace> faces;
+    std::function<void(int, const LegacyCanvasStrokePadRegionResult&, std::span<vertex_t>)> execute_face;
+};
+
+struct LegacyCanvasStrokePadExecutionResult {
+    bool ok = false;
+    std::size_t padded_faces = 0;
+};
+
 struct LegacyCanvasStrokeComputeRequest {
     StrokeSample previous_sample {};
     std::span<const StrokeSample> samples;
@@ -228,6 +246,47 @@ std::size_t execute_legacy_canvas_stroke_frame_faces(
     };
 }
 
+[[nodiscard]] inline LegacyCanvasStrokePadExecutionResult execute_legacy_canvas_stroke_pad_faces(
+    const LegacyCanvasStrokePadExecutionRequest& request)
+{
+    LegacyCanvasStrokePadExecutionResult result;
+    if (request.extent.width == 0U ||
+        request.extent.height == 0U ||
+        !request.execute_face) {
+        return result;
+    }
+
+    for (const auto& face : request.faces) {
+        if (!face.dirty) {
+            continue;
+        }
+
+        const auto pad_region = plan_legacy_canvas_stroke_pad_region(
+            LegacyCanvasStrokePadRegionRequest {
+                .extent = request.extent,
+                .pass_dirty_box = face.pass_dirty_box,
+            });
+        if (!pad_region.has_pixels) {
+            continue;
+        }
+
+        std::array<vertex_t, 6> pad_quad = {
+            vertex_t({ pad_region.ndc_quad[0].x, pad_region.ndc_quad[0].y }),
+            vertex_t({ pad_region.ndc_quad[1].x, pad_region.ndc_quad[1].y }),
+            vertex_t({ pad_region.ndc_quad[2].x, pad_region.ndc_quad[2].y }),
+            vertex_t({ pad_region.ndc_quad[3].x, pad_region.ndc_quad[3].y }),
+            vertex_t({ pad_region.ndc_quad[4].x, pad_region.ndc_quad[4].y }),
+            vertex_t({ pad_region.ndc_quad[5].x, pad_region.ndc_quad[5].y }),
+        };
+
+        request.execute_face(face.index, pad_region, pad_quad);
+        ++result.padded_faces;
+    }
+
+    result.ok = true;
+    return result;
+}
+
 [[nodiscard]] inline LegacyStrokeSampleExecutionResult execute_legacy_canvas_stroke_sample(
     const LegacyStrokeSampleExecutionRequest& request)
 {