docs: function OutlineFilter(thickness, color) {
      thickness = thickness || 1;
      PIXI.Filter.call(this,
          // vertex shader
          // vertex shader
          glslify('./outline.vert'),
          // fragment shader
          glslify('./outline.frag').replace(/%THICKNESS%/gi, (1.0 / thickness).toFixed(7))
      );
  
      this.uniforms.thickness = thickness;
      this.uniforms.outlineColor = new Float32Array([0, 0, 0, 1]);
      if (color) {
          this.color = color;
      }
  }