anchor: Texture:isReadable
  Gets whether the Texture can be drawn and sent to a Shader.
  
  Canvases created with stencil and/or depth PixelFormats are not readable by default, unless readable=true is specified in the settings table passed into love.graphics.newCanvas.
  
  Non-readable Canvases can still be rendered to.
  readable = Texture:isReadable()
  readable boolean Whether the Texture is readable.