How many visuals are there on your Silverlight and WPF app?
WPF uses retained mode graphical rendering model, this model is optimized for rendering a small portion of visual update, if you have say 4000 visuals on your scene, and you wanna update them all, WPF probably cannot render them smoothly, on the contrary, I guess Silverlight uses a immediate mode graphical rendering model, and it is suitable for large visual update.
So even if WPF is hardware accelerated, but at some unusual circumstance (such as the one I've mentioned above), WPF's rendering will probably be slower than its Silverlight counterpart.
As to the implementation of Silverlight's graphical rendering mechanism, I've heard that Microsoft comes up with a home made software rasterizer for Silverlight, the reason why don't use GDI here is that GDI cannot render video, and what's more, GDI doesn't support alpha channel blending. but after rasterizing the scene, Silverlight will end up using GDI to display the scene, this is in essence a normal bitblt operation indeed.
Sheva
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