the calculation of “iMouse.y” is wrong

[ZhiWang0413]

I find that the y component of property "iMouse" is wrong.

In the callback function of “mouseMove” and "mouseDown", the code is

# mouseMove
var mouseY = _this.canvasPosition.height - clientY - _this.canvasPosition.top - window.pageYOffset;
# mouseDown
var mouseY = _this.canvasPosition.height - clientY - _this.canvasPosition.top;

it should be

# mouseMove
var mouseY = _this.canvasPosition.height - clientY + _this.canvasPosition.top - window.pageYOffset;
# mouseDown
var mouseY = _this.canvasPosition.height - clientY + _this.canvasPosition.top;