Slow display performance of specific unicode characters

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• iTerm2 version: 3.0.4
• OS version: El Capitan 10.11.5 (15F34)
• Preferences: com.googlecode.iterm2.plist
• Debug log: debuglog.txt.gz
• Performance issue: Sample_of_iTerm2.txt (not sample was not taken when debug logging, but on separate run of test file)
• Test file: really_slow

Detailed steps to reproduce the problem:

1. Download really_slow to a directory
2. Go to that directory in iTerm and run the command cat really_slow

What happened: iTerm spends a lot of time drawing the characters in the file. Enough time to notice stuttering and lag. Scroll performance is also terrible.

What should have happened: The display of these characters should have been instant.

Looks related or identical to #4913 (closed)

Can you try the nightly build? While it's slower in general, it should be faster for issue #4913 (closed).

Here are both tests

3.0.4 with really_slow

$ time cat really_slow
<snip>
real	0m13.426s
user	0m0.003s
sys	0m0.009s

3.0.20160823-nightly with really_slow

$ time cat really_slow
<snip>
real	0m12.080s
user	0m0.003s
sys	0m0.009s

3.0.4

$ bash 4913.sh
real	0m1.032s
user	0m0.186s
sys	0m0.052s

Nightly

$ bash 4913.sh
real	0m1.693s
user	0m0.176s
sys	0m0.045s

Without more runs, the time different probably isn't significant.

I believe the solution may be the new adaptive framerate feature. Try this: turn on Prefs > Advanced > Use adaptive framerate and set When adaptive framerate is enabled, refresh at this rate during high throughput condition (FPS) to 5. You can experiment with that value to get different tradeoffs between performance and responsiveness. With these settings, I get:

real	0m0.178s
user	0m0.002s
sys	0m0.007s

Okay tried that out on nightly and it definitely has a good speed up. Will this issue be fixed at a lower level?

Eventually the adaptive framerate will be on by default. The problem is that text drawing is so slow in Cocoa that a reasonable frame rate doesn't leave time to process the input.

Milestone changed to %Feature Complete 3.1

closed