Bug 500861

Summary:	[Android] Brush strokes jitter if painted during canvas zoom out
Product:	[Applications] krita	Reporter:	Tyson Tan <tysontanx>
Component:	Brush engines	Assignee:	Krita Bugs <krita-bugs-null>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	dra.w.p.il.e+bugskde
Priority:	NOR
Version First Reported In:	5.2.9
Target Milestone:	---
Platform:	Android
OS:	Android 14.x
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Krita brush strokes jitter when painted zoomed out Brush strokes painted on Linux when zoomed out Extreme jitter if zoomed out to less than 12.5% and painted with smaller than 5mm circles

Description Tyson Tan 2025-02-28 11:58:41 UTC

On Android systems, if brush strokes were painted when the canvas is highly zoomed-out, they appear jittered at 100%, as if they were interpolated with a very low resolution.

Steps to reproduce"

1) Create a new document, A4 300ppi;
2) Zoom out the canvas to something lower than 12.5%;
3) Paint some small circles (approximately 5cm in diameter)
4) Zoom in to 100%

Expected result:
The brush strokes should appear smooth at 100%.

Actual result:
The brush strokes appear very jittered and unusable.

Tested on:
Samsung Galaxy Tab S8 (OneUI 6.1.1/Android 14)
Also confirm by other community users with Galaxy Tab S7

I will attach some examples on the following comments.

Comment 1 Tyson Tan 2025-02-28 12:03:10 UTC

Created attachment 178972 [details]
Krita brush strokes jitter when painted zoomed out

Comment 2 Tyson Tan 2025-02-28 12:07:56 UTC

Created attachment 178973 [details]
Brush strokes painted on Linux when zoomed out

This screenshot was captured on the Linux version using the same procedure and they look smooth and fine.

I deliberately tested this one on a Wacom One 13, which share the same Wacom EMR Pen technology with the Samsung Galaxy Tab S7 and S8 (all devices can share the same stylus). So I think we can rule out the possibility of low hardware resolution.

Reportedly, other art apps on Android are not affected by the same bug.

Comment 3 Tyson Tan 2025-02-28 12:09:42 UTC

I have also tested this bug with Krita 5.2.9 and the latest nightlies. All of them are affected on Android.

Comment 4 Tyson Tan 2025-02-28 12:15:44 UTC

Correction:

In the original description, Step 3) Paint some small circles (approximately 5cm in diameter)

It should be 5mm (which will resulted in extreme staircase like aliases).

And we have also tested this on Tab S7FE, S9+ and S9U.

Comment 5 Tyson Tan 2025-02-28 12:19:20 UTC

Created attachment 178974 [details]
Extreme jitter if zoomed out to less than 12.5% and painted with smaller than 5mm circles

Comment 6 dra.w.p.il.e+bugskde 2025-09-19 06:43:33 UTC

I can reproduce this both with a Samsung S-Pen and a Wacom Intuos tablet. However, this is because Android just doesn't have high-resolution input.

The reason other applications appear smoother is, from what I can tell, that they always compensate for low-frequency input and build a smooth curve, which as far as I can tell Krita does when you turn on the "Basic" brush stabilizer, resulting in a similarly smooth result. When I move the pen slowly in Ibis Paint or Drawpile, I get the same staircase effect, which shows that they're not receiving inputs at a higher resolution either.

So this needs to be fixed upstream, either the tablet manufacturers or Android would need to improve the input resolution. Users can enable a brush stabilizer to compensate for it in Krita.