Scratch-render: Some pen strokes result in large, blurred circles on iPhone Safari

Created on 15 Jun 2020  ·  6Comments  ·  Source: LLK/scratch-render

Expected Behavior

Pen strokes should not result in large, blurred circles.

Example:
IMG_0032

Actual Behavior

Pen strokes often result in large, blurred circles.

Example:
IMG_1562

Steps to Reproduce

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

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

High Severity Low Impact bug priority 3

Most helpful comment

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.

All 6 comments

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:
image

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:
image

(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.

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.

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

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.

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.

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