Cache visible image portion for painting

[cyotek]

Each time an ImageBox control paints itself, it goes through the job of picking part of the image, scaling it, and then painting it.

While this is normally fine, if you manually invalidate an image box repeatedly (for example when drawing custom adornments in reaction to user input), this can affect the responsiveness of the application.

It would probably be a better idea of the ImageBox control created a cached bitmap of the part of the image currently displayed and then used that for painting, and only invalidated this when the layout is impacted, e.g. scrolled, zoomed etc.

See this thread for a sample project I created which identified the issue.