Color touching color

colinbye · August 13, 2019, 11:06am

What browsers show this problem?

Chromium Version 76.0.3809.87 (Official Build) Built on Ubuntu , running on Ubuntu 18.04 (64-bit)

Also Firefox 68.0.1 (64-bit)

Please share an example project (if possible).

https://snap.berkeley.edu/snap/snap.html#present:Username=colinbye&ProjectName=touching%20problem

Describes the steps to reproduce this issue.

run project

What does Snap! currently do?

Depending on which direction the wagon sprite approaches the colours sprite the color touching block produces different answers

What should Snap! do instead?

Answer should be Touching regardless of direction

bh · August 13, 2019, 11:55pm

Hmm, works for me. Gang?

cymplecy · August 14, 2019, 1:16am

Doesn't work for me (e.g I get same issue as OP)
Win 10 Chrome

bromagosa · August 14, 2019, 9:12am

Fails here too. Here's a simplified version:

https://snap.berkeley.edu/snap/snap.html#present:Username=bromagosa&ProjectName=touching%20problem%20remix

dardoro · August 14, 2019, 10:06am

Fails in Chrome 75.0.3770.100 @Win 10 full screen
Works as expected in design mode with medium stage.
Don't work at all with small stage (always "not touching")

With default canvas antialiasing single source pixel makes colorful pattern. Resolution, color depth, stage scale may result in different pattern. Maybe there are even no single pixel with exactly this "yellow" touching "green".
Sometimes color matching can be based on range instead of exact. For ex: RGB values with stripped 1-2 lower bits.
Attached screen dump enlarged with Paint.

.
Maybe single pixel-wide objects on edge are unintenionally cropped by rouding of position and/or dimension. I made red pixel sticked to the yellow "nose" and color detection works flawless.

bh · August 14, 2019, 4:32pm

Ah, thanks for debugging it! Maybe it works for me because of my retina display.

It's tempting to turn off antialiasing and just live with jaggies but sharp edges.

dardoro · August 15, 2019, 3:00am

Under DEV mode there is color sensing with tolerance.
For me sensing with tolerance>0 works as expected for this case.

bh · August 15, 2019, 4:01am

Boy, you learn something every day! I guess this is something Jens is still playing with.

colinbye · August 15, 2019, 10:49am

I've looked further at this. I've modified the original sprite so that it now has blocks of solid colour and produced a simpler version of the project

https://snap.berkeley.edu/snap/snap.html#present:Username=colinbye&ProjectName=touching%20problem%202

This still displays the same behaviour.

Here's a blown up version of what appears when the sprite is to the right of the colour sprite and the project says Not Touching.

mastersun8 · August 15, 2019, 5:01pm

Checked different sprite positions and found that probably first row and first column of pixels is ignored during the touching test. Dad said it's probably a typical problem "does indexing start from 1 or from 0?".

dardoro · August 15, 2019, 6:44pm

I verified my son's findings and tested
Morph.prototype.isTouching@morphic.js with changed dimensions

.getImageData(0, 0, oImg.width, oImg.height)
This way it works as expected.

BTW. how to proceed bug submited by forum which lead to Guthub PR and
what should be "first choice" for submitting bugs: GH/Issues or this forum.
:

bh · August 16, 2019, 7:38am

Wow, thanks, team! A bug report with the solution attached is the best kind! :~)

If you have a Github account then Github is best. Certainly for a PR Github is essential. But this bug might not have been fixed so quickly if reported on Github, which has a smaller audience following Snap!, so I don't know for sure. A bug that doesn't get fixed here will end up copied to Github by one of the staff.

dardoro · August 19, 2019, 12:28am

Submited PR Sprite touching : first row, column included, Issue #2476 by DarDoro · Pull Request #2477 · jmoenig/Snap · GitHub

bh · August 19, 2019, 3:41am

Thank you!

susscrofa · August 20, 2019, 6:13am

Here:
Windows 10 with
FF 68.0.1 (64-Bit) > works fine
Chrome Version 76.0.3809.100 (Official Build) (64-bit) > works also fine
Sorry, I couldn't reproduce the problem.

dardoro · August 20, 2019, 8:54am

Can You try
https://snap.berkeley.edu/snap/snap.html#present:Username=dardoro&ProjectName=untouchables
with:
Browser zoom: 100%
Disabled Retina
Small stage (non full screen) or windowed browser (800x600 window)
OR
forced large stage dimension (it's prevents automatic sprite enlarge)

susscrofa · August 20, 2019, 10:57am

Yes, it seems to have something to do with the dithering of the sprites in smaller windows. Beyond a certain size (approx. 3 times the usual size) it works good, under that it doesn't touch.