Some pen strokes result in large, blurred circles on iPhone Safari

[RexScratch]

Expected Behavior

Pen strokes should not result in large, blurred circles.

Example:

Actual Behavior

Pen strokes often result in large, blurred circles.

Example:

Steps to Reproduce

On an iPhone, run one of the following projects on the project page:

• https://scratch.mit.edu/projects/278999727/
• https://scratch.mit.edu/projects/276932192/
• https://scratch.mit.edu/projects/318234147/
• https://scratch.mit.edu/projects/262564340/
• https://scratch.mit.edu/projects/236128688/

This doesn’t seem to be an issue limited to a few specific projects; most projects using the pen should produce this issue.

Operating System and Browser

iPhone XS iOS 13.5.1 Safari

Cannot reproduce on a 2019 iPad on iOS 13.5.1

[apple502j]

KimiruHamiru said it happens when the pen is down while the sprite x or y is not integer: see https://scratch.mit.edu/discuss/post/4123687/
repro project: https://scratch.mit.edu/projects/404686504/
on iPad:

[RexScratch]

KimiruHamiru said it happens when the pen is down while the sprite x or y is not integer: see https://scratch.mit.edu/discuss/post/4123687/
repro project: https://scratch.mit.edu/projects/404686504/
on iPad:

(Using Google Translate)

They mentioned using a iPad Mini 5, which is interesting because I couldn’t reproduce this issue on a 2019 iPad. The iPhone XS and iPad Mini 5 both have the A12 Bionic SoC, whereas the 2019 iPad has the A10 Fusion SoC.

[RexScratch]

It does seem that precision plays a role, since not all non-integer coordinates cause this issue:
https://llk.github.io/scratch-gui/develop/#404937682

When the x-coordinate is offset by -0.25 or -0.5, the issue doesn’t occur. However, when the x-coordinate is offset by -0.1, the issue does occur.

[fsih]

It's also reproing on iPhone 8, but not on iPad mini 4

[MineUp1000]

K, I noticed this glitch occurred recently and made a forum about it, but thankfully I was given this link!!!
(Thanks @apple502j). I think that this glitch occurred at the same time the Fullscreen Glitch Occurred

EDIT

This link, which I created myself is a test, which proves that the costume matters. (Ignore this)

I have made a new test, to see which fractions give the most glitches:
and this is thus result.

[RexScratch]

K, I noticed this glitch occurred recently and made a forum about it, but thankfully I was given this link!!!
(Thanks @apple502j). I think that this glitch occurred at the same time the Fullscreen Glitch Occurred

EDIT

This link, which I created myself is a test, which proves that the costume matters.

The only thing that test shows about costumes is that costumes can affect the sprite's position, which is already well-known.