Cursor runs ahead of the text that is being typed

[panta82]

Issue Type: Bug

Open a new blank file and paste this:

## Level 1

starthere

Then start typing after "starthere", in the same line. On my system, the cursor runs ahead of the text being typed.

See the gif:

Tried it on fresh install of the latest insider's edition, without extensions.

VS Code version: Code - Insiders 1.38.0-insider (c8d44e2, 2019-08-19T12:53:09.586Z)
OS version: Linux x64 4.9.0-9-amd64, XFCE on Debian 9.9

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz (12 x 4190)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software oop_rasterization: disabled_off protected_video_decode: unavailable_off rasterization: disabled_software skia_deferred_display_list: disabled_off skia_renderer: disabled_off surface_synchronization: enabled_on video_decode: unavailable_off viz_display_compositor: disabled_off webgl: enabled webgl2: enabled
Load (avg)	1, 1, 1
Memory (System)	31.37GB (0.28GB free)
Process Argv	--unity-launch
Screen Reader	no
VM	0%

Extensions: none

[alexdima]

@panta82 Are you using any form of zoom? Or a high DPI monitor? Is the cursor drawn correctly when setting "editor.disableMonospaceOptimizations": true ?

[alexdima]

related - #77817

[panta82]

@alexandrudima I am not using zoom, I was able to repro it on stock insiders edition, without any additional settings.

It's a 2K monitor. I can't repro the issue on my home HD monitor, so that might be it.

I will post more info tomorrow, when I get back to work, where the monitor is.

[panta82]

I just remembered I was supposed to post more info here :).

"editor.disableMonospaceOptimizations": true seems to solve the issue, but VSCode freezes after about a minute of playing around with this setting, and has to be killed by the system.

My feeling is that some miscalculation happens after typing for awhile. With disableMonospaceOptimizations, the editor freezes. Without, the incorrect character measurement is introduced, which exhibits like shown above.

My display settings are on the screenshot.

The bug is reproducible on either monitor.

[panta82]

Some more experimenting.

• It seems it doesn't matter which character I type.

• Everything seems fine at first, I can type multiple lines of characters without issues. But then I click around a bit, play with selection and then it happens. Afterwards, I can type anywhere, and characters will be incorrectly measured.

• If I open a new tab, and start typing, everything is fine in that tab (so the incorrect measurement is tied to a tab)

• I said above that disableMonospaceOptimizations causes editor to freeze. But now I managed to make it freeze without this setting at all, just by holding a single character for a while. Not sure if this is a separate issue or related (EDIT: I suspect freezing is related to the measurement issue).

[panta82]

I've installed version 1.28.2, which is the one my colleague uses successfully on a similar system. Both the freezing and misaligned cursor disappeared.

So the problem was introduced within the last 1 year.