ScaleManager#setResizeCallback()

Sets the callback that will be invoked before sizing calculations.

This is the appropriate place to call setUserScale if needing custom dynamic scaling.

The callback is supplied with two arguments scale and parentBounds where scale is the ScaleManager
and parentBounds, a Phaser.Rectangle, is the size of the Parent element.

This callback

• May be invoked even though the parent container or canvas sizes have not changed
• Unlike onSizeChange, it runs before the canvas is guaranteed to be updated
• Will be invoked from preUpdate, even when the game is paused

See onSizeChange for a better way of reacting to layout updates.