Best I can tell construct only provides the viewport* expressions to find the width of the view in layout coordinates.
The browser object, in the c2 docs at least, mention screenWidth and screenHeight as values too.
With js you can also get the width/height of the html canvas if you really want to handle it from scratch.
There’s also the system expressions layertocanvasx/y and canvastolayerx/y expressions that may be useful.
Does it only happen in full screen?
Honestly for positioning things don’t use absolutex/y. You can use it to see if the mouse moved.
Otherwise as an exercise in math you can map the absolute mouse position to the layout position in a correct way.
Intuitively you should be able to put your cursor sprite on any layer and position the sprite with
Set position to mouse(self.layer).x, mouse(self.layer).y
And it’ll just work, full screen or not. If it doesn’t then it’s a bug I say.
You can still utilize absolutex/y to check if there was mouse motion. Like
Global number oldx = 0
Global number oldy = 0
Compare oldx <> mouse.absolutex
Compare oldy <> mouse.absolutey
— do something because the mouse moved
— set oldx to mouse.absolutex
— set oldy to mouse.absolutey