Why is there a black lag every time a WPF window is resized?

Question

Other questions on SE address how to speed up nested UI control resizing, but- what if there aren\'t any controls?

As you drag the edge of a WPF window, even a main

Answer 1

The look is crummy indeed, especially when using the top or left border.

Which exact problem your screen shot is showing depends on how long your app is taking to render as well as a couple of background related settings that you might be able to tweak to get better resize. Plus part of the ugly resize is specific to Aero.

While I can't address the specific crazy slowness of WPF redraw, I can at least give some insight on why you see black, where that is coming from, and whether you can change to a less annoying fill-in color.

It turns out there are multiple different sources of the black and the bad resize behavior from different Windows versions that combine together. Please see this Q&A which explains what is going on and provides advice for what to do (again, not specific to making WPF faster but just seeing what you can do given the speed you have):

How to smooth ugly jitter/flicker/jumping when resizing windows, especially dragging left/top border (Win 7-10; bg, bitblt and DWM)?