Rendering randomly falls back into software

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=2052187&SiteID=1

but rather than hijack that thread more than I already have, I thought I'd start a new one on this topic, especially since it's really beginning to annoy me.

The basic issue is that depending on the Window size and apparently alot of other "unknown" factors, WPF randomly and without any apparent reason decides to fall back to software rendering. I can verify this using Perforator. I have created a relatively simple layout using a Viewbox and a Dockpanel. Sometimes I run the window and it remains rendered in hardware, even when the Window is Maximized. Other times, I resize the window even just a little and it immediately falls back into software. Same window, simply a different time that I double-click the exe file.

Sometimes it will fall back when video RAM usage is at 3.7 MB (for example); sometimes it waits until the usage is 8.3MB (for example). There is no apparent rhyme or reason to this behavior. It's important to me though, that my app be rendered in hardware as much as possible.

I don't mind periodic fallbacks but I don't want to expect hardware rendering when the app is fullscreen, and find users telling me the performance plummets - SOMETIMES - when they maximize the window.

Anyone else seen this behavior and/or is able to explain it?

Is this a performance issue that has been resolved in 3.5?

[1645 byte] By [PatrickSears] at [2008-1-10]