Rendering hardware, software how does it work in webkit?

Question

User interface

I make my interface render (for my needs).
At the moment, everything is drawn on the gpu using Direct2D.
For each element that has a color, text, etc, a texture is created.
At the end, all layers are overlaid with the DrawBitmap method.
And now the question.
I want all textures (bitmaps) to be in RAM, I will draw no matter what.
But the overlay of layers into the final result takes too long to do on the CPU.
So how can I make it so that I draw elements through cpu and apply layers through gpu?
Only Windows is considered.
---------------Minor question---------------
And suddenly, who knows how to properly implement dirty rectangles? At the moment, for this, I create a separate texture with the size of the current element and make a nugget before the element is drawn.

Answer 1

I want all textures (bitmaps) to be in RAM, I will draw no matter what.

Zadolbaye send textures back and forth.