Every repaint from CEF was encoded and sent to the terminal even when nothing had changed, and kitty frames were sent uncompressed. Five commits, each one usable on its own:
- Skip sixel frames identical to the one on screen. While a page is idle CEF keeps repainting; every one of those frames was byte for byte the previous one and cost about 100 ms of CPU and 650 KB of output.
- Disable smooth scrolling by default. Each scroll step was animated in about three frames that all had to be encoded. Adds
disable-smooth-scrollingto the default cef_flags.conf and bumps the config version, so existing configs are migrated (with the usual .bak). - Compress kitty frames and skip unchanged ones. A kitty frame was the whole page as raw RGB in base64, about 6.2 MB at 1600x980. zlib (
o=z, the existing compress_zlib at Z_BEST_SPEED) brings it to about 22 KB in 6 ms. - Do not blank the kitty image when clearing text. Forced redraws and closing dialogs used ED 2 and deleted the images before sending the next frame, so the screen was black until it arrived. The new frame is sent first and only the text is erased.
- Use a white background while pages load. The default windowless background is transparent, which showed as a black frame on every navigation.
Measured with the same harness before and after (1600x980, output sent to the terminal):
| Case | Before | After |
|---|---|---|
| yahoo.fr, 15 s idle (sixel) | 29 frames, 19.8 MB | 0 frames, 0 MB |
| Wikipedia, 10 presses of j (sixel) | 32 frames, 15.4 MB | 10 frames, 4.9 MB |
| Typing 20 characters (kitty) | 112 MB | 0.8 MB |
| Navigating in kitty, black captures out of ~690 in 12 s | 28 | 0 |
Tested in kitty 0.48.2 under Xvfb and in a real kitty, with sixel checked in a pseudo terminal and Konsole. Builds on current main and merges cleanly with the open pull requests.