我看过几篇文章在Swiftplaygrounds中展示GLKView，但我无法让它工作。我所看到的只是一个浅灰色的View。我希望它是蓝色的。我正在使用Xcode6.4importUIKitimportGLKitimportXCPlaygroundclassRGView:GLKView{overridefuncdrawRect(rect:CGRect){glClearColor(0.0,0.0,1.0,1.0)glClear(GLbitfield(GL_COLOR_BUFFER_BIT))}}letview=RGView(frame:CGRectMake(0,0,200,200),co