5 ms·

Why render with the GPU? I don't think I've seen a visually slow terminal emulator since 2000 and barely even in the 1990's. Text rendering is basically just b

by yason 8y ago

Why render with the GPU? I don't think I've seen a visually slow terminal emulator since 2000 and barely even in the 1990's. Text rendering is basically just blitting cached glyph bitmaps into a buffer, and CPUs have been more than overly fast doing that for eons. And CPU rendering has none of the compatibility problems/quirks that GPUs have. I can fire up a Gnome Terminal onto an unaccelerated Vesa X11 display if my graphics card doesn't work or I haven't configured it yet. For better responsivity I suppose a terminal that behaves like mosh would be a good approach. It would maintain the tty state in memory and only render the latest view, dropping the rendering of any intermediate diffs in the buffer. I would guess most terminal emulators do work like that these days but I haven't checked.

z3t4 8y ago
Text rendering is very complex. GPU text rendering is however unlikely to be faster then "native" text rendering. But it could likely make scrolling more smooth.
- yason 8y ago
  Rendering the vector fonts into cached bitmaps is complex. Rendering the final buffer by blitting those bitmaps isn't very. Smooth scrolling is inherently bounded by the vsync rate of the display. As long as you can render the terminal's pixel buffer with new characters and send it to front for the next flip, all within some portion of the time you have between frames, it's as smooth as it can get. Missing a frame will cause stutter, and make it non-smooth. Given the fact that terminal doesn't necessarily need to render if there are no changes, using GPU seems like an overkill for regular use.
- type0 8y ago
  You could use it to watch youtube in ascii mode if that somehow tickles your fancy
dancek 8y ago
Input latency makes for a bad user experience. People just usually don't notice it when typing as it's so common. See https://danluu.com/term-latency/ https://danluu.com/term-latency/ for measurements of some terminal software and discussion of why latency is bad. I'm not sure if Kitty is using GPU specifically to minimize latency, but it would be a good reason.
- tpolzer 8y ago
  Usually, offloading to the GPU will get you higher throughout but also higher latency. Although of course this assumes a sane software renderer, X11 API calls will take forever.
  - dancek 8y ago
    Really? It's counterintuitive considering the GPU draws the screen anyway. Is it because the shader pipeline has some inherent latency that a software renderer doesn't?
- simias 8y ago
  I work in video and as a consequence I tend to be very sensitive to latency (I've spent more hours than I can count trying to figure out subtle synchronization issues) yet I've just spent one minute trying to detect input latency on my st terminal (which fares pretty badly in the benchmark you linked) without success. And that's running inside tmux on top of that. That being said I think it is valuable to have a reasonably fast terminal because it's not uncommon to have applications slow down dramatically if they output a lot of information on stdout/stderr while the terminal struggles to render everything.
  - heavenlyblue 8y ago
    I don't know. Try using a simple, $2 (physical) calculator against the screen of your computer. I can definitely tell you that while I can't see the actual letter appearing on the screen - the letter on the calculator would feel as if it appeared right at the bottom position of the button, while on my PC the key would have travelled some distance off the ground before I see the letter. It's not uncomfortable, but I could easily tell the two apart in a blind test would something like that come up.
  - matt4077 8y ago
    I would have said the same, until I recently had to boot into an UEFI shell. Input was just so .... immediate? It’s really hard to describe, but it was surprisingly obviou.
kowdermeister 8y ago
Nearly all text rendering libraries I've checked uses the GPU.
- bno1 8y ago
  freetype definitely doesn't use the GPU and it's the most used font rendering library on Linux. What libraries did you check?
jillesvangurp 8y ago
Because on moder hdpi screens, text rendering involves pushing around a lot of pixels. Especially if you do stuff like having translucent windows, aliasing, complex font rendering, smooth scrolling, etc. So, it kind of makes sense to use the GPU for this. Of course on OSX, much of the desktop is already hardware accelerated so it is easy to overstate the impact here. Apple fixed this when they launched OSX in 2000 or so. I've been using iterm for years; when they introduced their metal rendering backend the impact was very subtle but noticable. Anyway, given the amount of time I spend using cli stuff, it kind of matters.

by yason 8y ago

z3t4 8y ago

Text rendering is very complex. GPU text rendering is however unlikely to be faster then "native" text rendering. But it could likely make scrolling more smooth.

yason 8y ago
Rendering the vector fonts into cached bitmaps is complex. Rendering the final buffer by blitting those bitmaps isn't very. Smooth scrolling is inherently bounded by the vsync rate of the display. As long as you can render the terminal's pixel buffer with new characters and send it to front for the next flip, all within some portion of the time you have between frames, it's as smooth as it can get. Missing a frame will cause stutter, and make it non-smooth. Given the fact that terminal doesn't necessarily need to render if there are no changes, using GPU seems like an overkill for regular use.
type0 8y ago
You could use it to watch youtube in ascii mode if that somehow tickles your fancy

dancek 8y ago

Input latency makes for a bad user experience. People just usually don't notice it when typing as it's so common. See https://danluu.com/term-latency/ https://danluu.com/term-latency/ for measurements of some terminal software and discussion of why latency is bad. I'm not sure if Kitty is using GPU specifically to minimize latency, but it would be a good reason.

tpolzer 8y ago
Usually, offloading to the GPU will get you higher throughout but also higher latency. Although of course this assumes a sane software renderer, X11 API calls will take forever.
- dancek 8y ago
  Really? It's counterintuitive considering the GPU draws the screen anyway. Is it because the shader pipeline has some inherent latency that a software renderer doesn't?
simias 8y ago
I work in video and as a consequence I tend to be very sensitive to latency (I've spent more hours than I can count trying to figure out subtle synchronization issues) yet I've just spent one minute trying to detect input latency on my st terminal (which fares pretty badly in the benchmark you linked) without success. And that's running inside tmux on top of that. That being said I think it is valuable to have a reasonably fast terminal because it's not uncommon to have applications slow down dramatically if they output a lot of information on stdout/stderr while the terminal struggles to render everything.
- heavenlyblue 8y ago
  I don't know. Try using a simple, $2 (physical) calculator against the screen of your computer. I can definitely tell you that while I can't see the actual letter appearing on the screen - the letter on the calculator would feel as if it appeared right at the bottom position of the button, while on my PC the key would have travelled some distance off the ground before I see the letter. It's not uncomfortable, but I could easily tell the two apart in a blind test would something like that come up.
- matt4077 8y ago
  I would have said the same, until I recently had to boot into an UEFI shell. Input was just so .... immediate? It’s really hard to describe, but it was surprisingly obviou.

kowdermeister 8y ago

Nearly all text rendering libraries I've checked uses the GPU.

bno1 8y ago
freetype definitely doesn't use the GPU and it's the most used font rendering library on Linux. What libraries did you check?

jillesvangurp 8y ago

Because on moder hdpi screens, text rendering involves pushing around a lot of pixels. Especially if you do stuff like having translucent windows, aliasing, complex font rendering, smooth scrolling, etc. So, it kind of makes sense to use the GPU for this. Of course on OSX, much of the desktop is already hardware accelerated so it is easy to overstate the impact here. Apple fixed this when they launched OSX in 2000 or so. I've been using iterm for years; when they introduced their metal rendering backend the impact was very subtle but noticable. Anyway, given the amount of time I spend using cli stuff, it kind of matters.