Changed mouse button to object

[diyaayay]

Resolves processing#6847

Changes:

• Changed mouseButton from a string to object.
• mouseButton now intends to track the current state of mouse buttons, showing which buttons are pressed at any given moment.

This work is done over the PR processing#7378

PR Checklist

• npm run lint passes
• Inline documentation is included / updated
• Unit tests are included / updated

[davepagurek]

It looks like if you have two fingers down, and then raise one, this would cause mouseButton.left to become false because the pointer that was lifted would now have no left button. It might be prefereable to, when this happens, keep mouseButton.left true if any remaining touch still has a left button down.

So maybe that would mean adding a buttons property on each active touch, and when an event happens, we loop through activeTouches and set left = activeTouches.some(touch => touch.buttons.left)? (I think this would also mean using activeTouches for all pointer types, not just touch, to still handle the single-pointer desktop case correctly.

Does that behaviour sound like what we want?

[diyaayay]

I think it makes more sense for mouseButton.left to remain true as long as any touch action is present on the screen. Setting it to false in onpointerup, using something like this, might work well:

if (this._activeTouches.size === 0) {
  Object.keys(this.mouseButton).forEach((key) => (this.mouseButton[key] = false));
}

This approach means we treat all active touches on the screen as left touches, correct? In that case, right and center clicks would only be supported by a mouse if I'm not wrong.