4 ms·

That really doesn't explain the why though. Why is pixel fill so slow? You'd expect the opposite given the numbers on graphics cards. What's the disconnect here

• bsder 3y ago
  Honestly, it's not "slow", it's just there are a LOT of pixels. Number of pixels goes up roughly as the square of resolution. A 4K monitor is 4x the pixels of a 1080p monitor. 8K is 16x the pixels of a 1080p monitor. My current browser window is probably more pixels than 2 1080p monitors. Doing the math: 1920x1080x2x4bytes(RGBA) = roughly 16 megabytes On a 3070 (a quite solid graphics card) you get roughly 450GB/s of memory bandwidth. That's if everything is up, running, powered, and in order. You wind up with 16MB/450000MB/s = 35uS for a simple window clear. Nothing clever just a pure write clear. That's 3+ orders of magnitude off from CPU operations. If you have to do a blend op, you have 3x--read byte, operate on byte with other data and write back. You've just crossed 100uS for the simplest blend--if you get all the memory interleaved correctly AND nothing has to leave the graphics card (if you have to transfer between the card and CPU you can kiss your time budget goodbye). It's one of the reasons why "compositing" is such a PITA. And, to be honest, I suspect compositing window managers are a dead end. Do we really need animated window opening and closing effects? Do windows really need to be transparent so you can see something behind? Do we really need greyscale, blended drop shadows on the edges? Do we really need to render the contents of the window while resizing it? The mobile space answers "Oh, hell, no." The tiling window manager users also concur. 8K is just going to make this kind of stuff disastrously obvious.