In what scenarios does freezing WPF objects benefit performance greatly?
Many types in WPF derive from Freezable. It provides immutability to mutable POCO objects and, apparently, allows for improved performance in certain situations.
Has anyone found that freezing objects within their WPF application has greatly improved performance? If so, then which items gave the biggest performance difference when being frozen?
(Note that I have posted a similar but different question too)
Answer
You might be interested in my experiences with Freezable:
I once wrote a PDF viewer using muPdf which renders bitmaps, that I render with WPF. What helps performance greatly is that I can render the page bitmaps on a background thread, freeze them, and then pass them to the UI thread. It is nice that WPF does not copy the image to freeze it, but the ability to do all this preparation on a background thread was the key benefit for me.
From what I understand, all visuals need to be frozen so they can be safely rendered by the WPF render thread. If you render large unfrozen visuals, they will get cloned to frozen ones when WPF renders them. If you freeze your static bitmaps beforehand, WPF can just share the pointer with the render thread without cloning. Unfrozen objects may even get copied repeatedly if WPF is not aware wether the object is changed from the last time it was rendered. Frozen objects eliminate the need for all this copying.