I'm developing a large-scale application with a custom rendering system. The system has a dedicated rendering thread that draws a specific region of a virtual canvas into a temporary memory buffer. Then, in the OnRender() method, I use WritableBitmap.WritePixels() to update the image content, and draw it to a specified screen region using DrawingContext.DrawImage()

During user interactions such as mouse dragging, the draw region changes in real time, but the actual image content is not necessarily updated on every OnRender() call.

I've noticed that occasionally, the image content does not match the drawn region, resulting in visible "jumps" or flickering during dragging. This issue is especially noticeable on my 4K display with integrated graphics, full-screen window, where the flickering happens frequently.

Interestingly, I encountered the same issue when previously using InteropBitmap, which also involves a updating image data mechanism. This leads me to believe the issue is related to how images with such updating mechanisms.

When I switched to creating a new BitmapSource in every 'OnRender()' call and drawing it directly—without using WritableBitmap—the issue disappeared entirely. This strongly suggests that WritableBitmap.WritePixels() is not synchronized with the OnRender() pipeline under certain conditions.

I also tried using Dispatcher.Invoke with DispatcherPriority.Render to call WritePixels(), but the problem persists.

It seems that under heavy rendering load, the image updated by WritePixels() might not be synchronized with the draw operation in OnRender(), leading to this visual mismatch.

How can I avoid this timing issue while still using WritableBitmap?