Pinch to zoom not working anymore

[clementcontet]

Describe the bug

Since the migration from Blockly 6.2 to Blockly 9, the pinch to zoom doesn't work for me on touch devices.

To Reproduce

Visit https://www.supercodingball.com/code/offline/do-nothing on a touch device (or clone and run https://github.com/Orange-OpenSource/super-coding-ball on a touch device).

Expected behavior

I may do something wrong but I can't figure out what.

The pinch setting is still there: https://github.com/Orange-OpenSource/super-coding-ball/blob/d86a9d3dd2bdf4830518bac607a0e347ff380e86/src/app/components/blockly/blockly.component.ts#L83

Smartphone (please complete the following information):

• Chrome Android

[clementcontet]

In console, I get the following warning: 'Tried to start the same gesture twice.'
I've tried https://blockly-demo.appspot.com/static/demos/code/index.html on a mobile device and I get the same error.

[maribethb]

I've done a git bisect and #6099 is the culprit, still working on root causing. Using BrowserStack Local for testing and it's slow going. Using the debugger doesn't work all that well because the gesture changes when the debugger is in play (e.g. it thinks I'm long pressing instead of pinching)

What I've found so far is that in blockly-v8.0.5, in browserEvents.conditionalBind the wrapped function (in this case, workspaceSvg.onMouseDown_) is called twice, each time with one event in the array returned by Touch.splitEventByTouches. But the second time the wrapped function is called, Touch.shouldHandleEvent returns false, so we continue out of the loop and the event handler is not actually called a second time.

On develop, the wrapped function is called twice, each time with one event in the array. But this time, Touch.shouldHandleEvent returns true both times, causing the event handler to get called twice, causing the "tried to start the same gesture twice" message.

I don't yet know why Touch.shouldHandleEvent behaves differently, since that function nor the two it calls seem changed by #6099 at first glance, but this will be investigation for tomorrow.

[maribethb]

root cause found: https://github.com/google/blockly/blob/1162a660a0cfe9ff2acdbed5ee66246d3bd5beb2/core/touch.ts#L167-L173

PointerEvent is a subclass of MouseEvent, so the touch identifier is always set to 'mouse' if pointer events are supported. This causes shouldHandleEvent to always think we are talking about the same touch point, and says we should always handle the touch event.

PR incoming (after more testing is done)