[Dylan16807]

In this use case the "painting" a compositor does from layers is copying one big rectangle. That takes next to zero time. That's not at all similar to "painting" where you actually re-render the entire visible portion of the page.

[pcwalton]

> That's not at all similar to "painting" where you actually re-render the entire visible portion of the page.

Why not?

Painting a page is mostly just copying pixels from textures too.

[Dylan16807]

You don't see a notable difference between [tens of] thousands of glyphs and bits being layered on top of each other and processed through a display list, versus copying over one single rectangle from A to B?

[pcwalton]

No, I don't. It adds a small amount of vertex shading time. The GPU primitive rasterization machinery is extremely good.

Benchmark it yourself if you don't believe me!