Route RTT region readbacks through backend

src/canvas_actions.cpp

@@ -92,22 +92,12 @@ Action* ActionStroke::get_redo()
         {
             action->m_image[i] = std::make_unique<uint8_t[]>(
                 static_cast<size_t>((int)box_sz.x) * static_cast<size_t>((int)box_sz.y) * 4U);
-            App::I->render_task([&]
-            {
-                const auto pixel_format = pp::renderer::gl::rgba_pixel_format();
-                const auto component_type = pp::renderer::gl::unsigned_byte_component_type();
-
-                layer->rtt(i, m_frame_idx).bindFramebuffer();
-                glReadPixels(
-                    (int)box_or.x,
-                    (int)box_or.y,
-                    (int)box_sz.x,
-                    (int)box_sz.y,
-                    pixel_format,
-                    component_type,
-                    action->m_image[i].get());
-                layer->rtt(i, m_frame_idx).unbindFramebuffer();
-            });
+            layer->rtt(i, m_frame_idx).readPixelsRgba8(
+                static_cast<int>(box_or.x),
+                static_cast<int>(box_or.y),
+                static_cast<int>(box_sz.x),
+                static_cast<int>(box_sz.y),
+                action->m_image[i].get());
         }
         else
         {