onDidChangeTextEditorVisibleRanges shows strange behaviour!

[moalamri]

Issue Type: Bug

I've been working with onDidChangeTextEditorVisibleRanges event lately and I have noticed few things, I will explain with code example and some different cases:

	let eventCounter: number = 0

	vscode.window.onDidChangeTextEditorVisibleRanges((event) => {
		eventCounter++
		console.log('Event trigger count:', eventCounter);
		event.visibleRanges.forEach((range) => {
			console.log('Start line:', range.start.line)
			console.log('End   line:', range.end.line)
		})
	})

As per documents

An Event which fires when the visible ranges of an editor has changed.

In my case, the event is fired as expected, but with the following condition only; when I navigate (scroll around) the editor, either by mouse or keyboard arrows in an existing open text editor.

However, the strange behaviour only happens with newly opened text editor and when switching to a different tab.
To simplify it, Assuming that I have the editor max visible range of 33 lines:

• (A) It doesn't fire when a text editor is newly opened from the workspace files (I don't know if it should be!). I mentioned newly as the text editor's active cursor location and visible ranges are not memorized.
• (B) It fires when the opened text editor has the cursor location in memory, except that:
  • (B.1) It fires one time but only when the cursor location is within 1-33 and the memorized visible range (scroll location?) first visible line is greater than 2
  • (B.2) It doesn't fire at all when the memorized cursor location is within the first lines of the editor (from 1 to editor's max visible range which is 33 lines in my case). So, if the cursor location is within 1-33 the event won't be fired no matter what the total lines count of the file.
  • (B.3) It fires twice when the memorized cursor location is greater than 33 no matter where the memorized visible range is, the first trigger will have visible range start from the cursor location minus 33. however, the second trigger will have the correct visible range.

Using the above code and mentioned cases:

Example for case (B.1) it prints the following:

Event trigger count: 1
Start line: 2
End   line: 34

Example for case (B.2) it prints nothing

Example for case (B.3) it prints the following:

Event trigger count: 1
Start line: 61
End   line: 94

Event trigger count: 2
Start line: 71
End   line: 104

VS Code version: Code 1.69.0 (92d25e3, 2022-07-07T05:28:36.503Z)
OS version: Windows_NT x64 10.0.22000
Restricted Mode: No

System Info

Item	Value
CPUs	AMD Ryzen 7 4800H with Radeon Graphics (16 x 2895)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled
Load (avg)	undefined
Memory (System)	15.37GB (7.84GB free)
Process Argv	--crash-reporter-id d50e185c-0bfc-44b6-9830-5d4a2c2c6978
Screen Reader	no
VM	0%

Extensions: none (1 theme extensions excluded)

[vscodenpa]

Thanks for creating this issue! It looks like you may be using an old version of VS Code, the latest stable release is 1.69.1. Please try upgrading to the latest version and checking whether this issue remains.

Happy Coding!

[moalamri]

Thanks for creating this issue! It looks like you may be using an old version of VS Code, the latest stable release is 1.69.1. Please try upgrading to the latest version and checking whether this issue remains.

Happy Coding!

Hello bot :) I did upgrade and still the same.
Just to mention I have been experiencing this behaviour since version 1.68.0 (I haven't used the API before) up to version 1.69.1

[moalamri]

@alexdima
A quick reproduce
https://github.com/moalamri/test-events

[tomByrer]

Any progress please? Affecting other plugins:
https://github.com/mtbaqer/vscode-better-folding#known-issues

[moalamri]

@tomByrer @mtbaqer. This issue seems to be neglected, even though it doesn't only affect extensions creator, but also VS Code performance.
Right now, the only workaround is a debouncing class to limit excessive events and to get the right ranges. You can get the code from here, it is self-explanatory, and you can check the extension.ts file to see the implementation.