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zed-industries / zed

Code at the speed of thought – Zed is a high-performance, multiplayer code editor from the creators of Atom and Tree-sitter.
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GPUI overdraws too much #8043

Open kvark opened 9 months ago

kvark commented 9 months ago

Check for existing issues

Describe the bug / provide steps to reproduce it

zed-overdraw

It looks like most "ordinary" pixels are being overdraw 5-6 times on screen. See screenshot from RenderDoc's "pass overdrawn" mode. I looked at the green area (5 draws per pixel) and at the yellow one on the left (6 draws per pixel). This is burning GPU power too much unnecessarily and draining the battery.

Ideally, these areas would have 0 to 1 draw. 0 is possible because the render pass is starting with a clear color. For elements overlapping each other, there needs to be some technique for pixel rejection employed. Generally it's depth or stencil testing. For example, WebRender draws opaque elements from front to back and writes to depth, preventing deeper layers from overwriting the pixels of the front layers.

Environment

Linux (but it unlikely matters)

jansol commented 9 months ago

I'm not sure GPUI has anything fully opaque? Since practically all elements are antialiased rounded rectangles which require alpha blending.

kvark commented 9 months ago

@jansol not all elements have rounded corners. For example, #7231 makes the fast path for such quads that are just quads, and it makes a good difference. In WebRender we'd also split a rounded-cornered element into a "9 patch", which consists of 5 fully opaque rectangles and 4 semi-transparent rectangles. This allows drawing most of the element early as opaque.

jansol commented 9 months ago

Right, makes sense. And I assume it just skips elements with a non-opaque background color.

github-actions[bot] commented 2 months ago

Hi there! 👋 We're working to clean up our issue tracker by closing older issues that might not be relevant anymore. Are you able to reproduce this issue in the latest version of Zed? If so, please let us know by commenting on this issue and we will keep it open; otherwise, we'll close it in a week. Feel free to open a new issue if you're seeing this message after the issue has been closed. Thanks for your help!

jansol commented 2 months ago

AFAIK there has been no change to this.

someone13574 commented 1 month ago

In WebRender we'd also split a rounded-cornered element into a "9 patch", which consists of 5 fully opaque rectangles and 4 semi-transparent rectangles.

Wouldn't you only need three fully opaque?

kvark commented 1 month ago

Yes, you can make just 3 opaque.