Extract stroke draw pad face helper

tests/paint_renderer/compositor_tests.cpp

@@ -2009,6 +2009,58 @@ void legacy_canvas_stroke_pad_destination_dispatch_preserves_order(pp::tests::Ha
     PP_EXPECT(h, steps == expected);
 }
 
+void legacy_canvas_stroke_pad_face_callbacks_preserve_order(pp::tests::Harness& h)
+{
+    std::vector<std::string> steps;
+    const auto padded_faces = pp::panopainter::execute_legacy_canvas_stroke_pad_face_callbacks(
+        std::array {
+            pp::panopainter::LegacyCanvasStrokePadFace {
+                .index = 2,
+                .dirty = true,
+                .pass_dirty_box = glm::vec4(1.f),
+            },
+        },
+        pp::renderer::Extent2D { 64U, 32U },
+        true,
+        [&](std::span<const vertex_t> pad_quad) {
+            steps.emplace_back("upload:" + std::to_string(pad_quad.size()));
+        },
+        [&](int face_index) {
+            steps.emplace_back("begin:" + std::to_string(face_index));
+        },
+        [&](int face_index) {
+            steps.emplace_back("bind:" + std::to_string(face_index));
+        },
+        [&](const pp::paint_renderer::CanvasStrokeCopyRegion& copy_region) {
+            steps.emplace_back(
+                "copy:" + std::to_string(copy_region.x) + "," +
+                std::to_string(copy_region.y) + "," +
+                std::to_string(copy_region.width) + "," +
+                std::to_string(copy_region.height));
+        },
+        [&](int face_index) {
+            steps.emplace_back("unbind:" + std::to_string(face_index));
+        },
+        [&] {
+            steps.emplace_back("draw");
+        },
+        [&](int face_index) {
+            steps.emplace_back("finish:" + std::to_string(face_index));
+        });
+
+    const std::vector<std::string> expected {
+        "upload:6",
+        "begin:2",
+        "bind:2",
+        "copy:0,0,64,32",
+        "draw",
+        "unbind:2",
+        "finish:2",
+    };
+    PP_EXPECT(h, padded_faces == 1U);
+    PP_EXPECT(h, steps == expected);
+}
+
 void plans_canvas_stroke_commit_erase_sequence(pp::tests::Harness& h)
 {
     const auto plan = plan_canvas_stroke_commit_sequence(