anchor: love.graphics.stencil
  Draws geometry as a stencil.
  
  The geometry drawn by the supplied function sets invisible stencil values of pixels, instead of setting pixel colors. The stencil buffer (which contains those stencil values) can act like a mask / stencil - love.graphics.setStencilTest can be used afterward to determine how further rendering is affected by the stencil values in each pixel.
  
  Stencil values are integers within the range of 255.
  love.graphics.stencil( stencilfunction, action, value, keepvalues )
  stencilfunction function Function which draws geometry. The stencil values of pixels, rather than the color of each pixel, will be affected by the geometry.
  action ('replace') StencilAction How to modify any stencil values of pixels that are touched by what's drawn in the stencil function.
  value (1) number The new stencil value to use for pixels if the 'replace' stencil action is used. Has no effect with other stencil actions. Must be between 0 and 255.
  keepvalues (false) boolean True to preserve old stencil values of pixels, false to re-set every pixel's stencil value to 0 before executing the stencil function. love.graphics.clear will also re-set all stencil values.