Mouse buttons and wheels

[Ken Rose]

Attached is a patch to allow Elm programs to distinguish among the three mouse buttons and to read the mouse wheels.  It leaves the current mouse interface unchanged, but add calls to report specific button presses and to report wheel motions.  The Javascript mouse interface defines three wheels, and this reports a triple of all three.  The middle one is the normal one we're all used to.  The new interface is:

module Mouse
    ( position, x, y
    , isDown, clicks
    , isLDown
    , isCDown
    , isRDown
    , wheel
    )

Mouse.isLDown, Mouse.isCDown, and Mouse.isRDown report status for the left, center, and right buttons, respectively.  Mouse.wheel reports a triplet of type (Int,Int,Int) for the three wheel components (X_wheel, Y_wheel, Z_wheel).  As I mentioned, the normal wheel/button is the Y wheel.

Someone with full familiarity with the cross-browser issues should review this, though it works for me, in the cases I've tried.

I'm amazed this hasn't been done before.

 - ken