Add checkbox in palette for mouse x and y

[ntlrsk]

It would be helpful to have a checkbox to show a monitor for mouse x and mouse y. on the Stage, since those values are no longer visible below the Stage.

More info: For the pong game, the paddle is set to mouse x. The way to explain that would be to point to the numbers changing below the stage as the mouse moved. Since those are no longer there, being able to check the box and see those change would be helpful.

[thisandagain]

From testing this has some fairly serious implications on performance (which is probably why we don't have monitors for mouse x/y position in 2.0). I'm going to backlog these with "needs-discussion" so we can discussion solutions in the future.

[towerofnix]

@thisandagain Scratch 2.0 does have sprite x/y position monitors:

From testing this has some fairly serious implications on performance

I'm curious about these. Is the issue related to updating the DOM for a monitor every tick / whenever a sprite moves? I'd like to mention #1397, which discusses moving monitors into the renderer; this could solve some problems.

Also, I could just do this:

This does not cause any lag. So why would "mouse x" and "mouse y" monitors cause lag?

[thisandagain]

@towerofnix Sorry. That was a typo ... I meant mouse x/y monitors.

[towerofnix]

@thisandagain Yeah, figured :)

I'm curious about the difference between showing/updating a variable monitor versus a mouse-X/Y watcher?