When should WS_EX_NOREDIRECTIONBITMAP be used?

Question

MSDN says (Extended Window Styles):

WS_EX_NOREDIRECTIONBITMAP: The window does not render to a redirection surface. This is for windows t

Answer 1

WS_EX_NOREDIRECTIONBITMAP is for windows that use DirectComposition for rendering.

E.g. Sciter creates windows with WS_EX_NOREDIRECTIONBITMAP to support Acrylic composition effects like here:

This is an ordinary Win32 window (not UWP) that uses DirectComposition and WS_EX_NOREDIRECTIONBITMAP.

Rendering on such windows should be done by Direct2D means. GDI rendering is barely useful with WS_EX_NOREDIRECTIONBITMAP.

Answer 2

DirectComposition is the main api that you can use to draw a window with no redirection bitmap. DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL on swapchains without DirectComposition might also trigger this mode.

One thing to worry about when using the api is that there won't necessarily be an opaque window background, so dwm can do a lot of extra work blending with things behind the window that aren't actually not visible