code: func (c *Context) Viewport(x, y, width, height int) {
  	c.Call("viewport", x, y, width, height)
  }
docs: // public function vertexAttrib1f(indx:GLuint, x:GLfloat) : Void;
  // public function vertexAttrib2f(indx:GLuint, x:GLfloat, y:GLfloat) : Void;
  // public function vertexAttrib3f(indx:GLuint, x:GLfloat, y:GLfloat, z:GLfloat) : Void;
  // public function vertexAttrib4f(indx:GLuint, x:GLfloat, y:GLfloat, z:GLfloat, w:GLfloat) : Void;
  // public function vertexAttrib1fv(indx:GLuint, values:ArrayAccess<Float>) : Void;
  // public function vertexAttrib2fv(indx:GLuint, values:ArrayAccess<Float>) : Void;
  // public function vertexAttrib3fv(indx:GLuint, values:ArrayAccess<Float>) : Void;
  // public function vertexAttrib4fv(indx:GLuint, values:ArrayAccess<Float>) : Void;
  // Represents a rectangular viewable area that contains
  // the rendering results of the drawing buffer.