pointerup is defined to be when a {finger,stylus} loses contact with the screen or when mouse buttons are no longer being pushed. Therefore, I'd expect the pressure value of every pointerup event to be 0. Moreover, the spec requires pressure to be 0 if the hardware doesn't support it and no buttons are active (that is, the pointer is up).

Maddeningly, its actual value is different across implementations. Here's the current breakdown:

And here's the test. If the background turns green on pointerup, pressure is 0. If it turns red, pressure is using a stale value from pointermove.

tl;dr:

• Firefox always sets pressure to 0 in pointerup.
• The other desktop browsers use 0 for stylus and trackpad, but the last pointermove value for touch.
• iOS and Android both use the last pressure value from pointermove.

Can we please explicitly declare in the spec that pressure should be 0 in every pointerup? This would be consistent with the currently specified behavior for pointers that don't granularly report pressure.

Here are the relevant bugs:

• Chrome
• PEP