docs: function ColorMatrixFilter()
  {
      core.AbstractFilter.call(this,
          // vertex shader
          null,
          // fragment shader
          fs.readFileSync(__dirname + '/colorMatrix.frag', 'utf8'),
          // custom uniforms
          {
              m: { type: '1fv', value: [1, 0, 0, 0, 0,
                                      0, 1, 0, 0, 0,
                                      0, 0, 1, 0, 0,
                                      0, 0, 0, 1, 0,
                                      0, 0, 0, 0, 1] },
          }
      );
  }