Is there a way in Windows Phone 8.1 RT to code my own page transitions and how low level and fancy can I get?
I'm not talking about being able to pick between sliding and turnstile transitions. More like coding a custom shader that uses a bit mask to interpolate between two frames over time.
Say i wan't to create a transition that burns the top page away.
I've tried to google some tutorials but I am having a hard time finding any.
You should probably take a look at combining DirectX with XAML, for which you have plenty of resources online. This is the lowest you can get, and super powerful. For C# there is a popular wrapper called SharpDX which could make things easier.
Another option could be the Win2D API.
Additionally you should reimplement the Frame control which would handle the new content animations properly.
Seems like a lot of work tough.