InputHandler#pixelPerfectClick

Set to true to use pixel perfect hit detection when checking if the pointer is over this Sprite when it's clicked or touched.
The x/y coordinates of the pointer are tested against the image in combination with the InputHandler.pixelPerfectAlpha value.
This feature only works for display objects with image based textures such as Sprites. It won't work on BitmapText or Rope.
Warning: This is expensive so only enable if you really need it. Use a pixel perfect check when testing for clicks or touches on the Sprite.