如何在iPhone上激活OpenGL ES中的多重采样？

// 创建帧缓冲对象
glGenFramebuffers(1, &_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);

// 创建多重采样纹理
glGenTextures(1, &_multisampleTexture);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, _multisampleTexture);
glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, 4, GL_RGBA, width, height, GL_TRUE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, _multisampleTexture, 0);

// 创建多重采样渲染缓冲对象
glGenRenderbuffers(1, &_multisampleRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _multisampleRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_DEPTH24_STENCIL8_OES, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, _multisampleRenderbuffer);

// 解绑帧缓冲对象
glBindFramebuffer(GL_FRAMEBUFFER, 0);