Infinite loop when handling 'pointermove' events.

[mikeharv]

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Description

Users get RangeError: Maximum call stack size exceeded if they attempt to drag a block with multiple fingers on a workspace where zoom controls/wheel are disabled.

My understanding of these two functions is as follow:

1. handleMove Function:

   • Checks if the gesture is a drag or a multi-touch event
   • If it's a multi-touch event, it calls handleTouchMove.

2. handleTouchMove Function:

   • Updates cached touch points and checks for pinch zoom conditions.
   • If the conditions for pinch zoom are not met, it calls handleMove again.

If there's a multi-touch event that doesn't meet the conditions for a pinch zoom, an infinite loop is created.

Code.org use NewRelic to detect JS errors like this. Since migrating two more labs to Google Blockly this week (:tada:), the errors have been above our threshold causing an alarm. This alarm pages our on-call engineer.

In order to fix this, I was able to monkey-patch handleMoveTouch to independently handle the touch events without needing to call handleMove again: code-dot-org/code-dot-org#59864

Reproduction steps

1. On a touch device, go to the advanced playground.
2. Disable zoom wheel and controls
3. Add block to the workspace.
4. Using two fingers, attempt to drag the block.
5. Observe the range error in the console.

Stack trace

[Error] RangeError: Maximum call stack size exceeded.
	handleTouchMove (blockly_compressed.js:733)
	handleMove (blockly_compressed.js:730:349)

...repeats infinitely...

Screenshots

Browsers

No response

[cpcallen]

Hi @mikeharv. Thanks for finding this. We'd take a patch for it, if you would be so kind as to submit one.

[AbhinavKRN]

@mikeharv can you assign this issue to me?

[mikeharv]

@cpcallen We've been running this patch for a couple weeks without any reported issues: https://github.com/code-dot-org/code-dot-org/blob/189a4fd5e223ffebcaf19677d0d9788e13a52625/apps/src/blockly/addons/cdoGesture.js

It does repeat some code shared by handleMove, but if you like the approach I'm happy to find a time to submit.

@AbhinavKRN I do not have permissions to assign issues from this repository, sorry!

[AbhinavKRN]

@mikeharv whom to contact then?

[BeksOmega]

Hiya @AbhinavKRN if you're still interested feel free to give this a shot!

[AbhinavKRN]

@BeksOmega On it!

[AbhinavKRN]

@BeksOmega Can you let me know in which typeScript file do I get to read the code of handleTouch function and handleMoveTouch function

[BeksOmega]

@BeksOmega Can you let me know in which typeScript file do I get to read the code of handleTouch function and handleMoveTouch function

Did you try searching for those strings in this repo? https://github.com/search?q=repo%3Agoogle%2Fblockly%20handleTouchMove&type=code