ios - 为什么向我的应用程序添加多重采样会在第一帧卡住屏幕？

Question

我正在尝试将多重采样添加到我的应用程序中，但似乎我犯了一个错误，但我找不到我做错了什么。

这就是我设置帧缓冲区和渲染缓冲区的方式

- (void)setupBuffers {
    glGenFramebuffers(1, &_framebuffer);
    glGenRenderbuffers(1, &_renderbuffer);

    glBindFramebuffer(GL_FRAMEBUFFER, _framebuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, _renderbuffer);

    [_context renderbufferStorage:GL_RENDERBUFFER fromDrawable:_eaglLayer]; // I already set the current context to _context, and _eaglLayer is just self.layer

    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _renderbuffer);

    if (YES) { // note if I set this to no, my app properly displays (I don't even have to remove the code in my render method)
        glGenFramebuffers(1, &_msaa_framebuffer);
        glGenRenderbuffers(1, &_msaa_renderbuffer);

        glBindFramebuffer(GL_FRAMEBUFFER, _msaa_framebuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, _msaa_renderbuffer);

        glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 2, GL_RGBA8_OES, [AppDelegate screenWidth], [AppDelegate screenHeight]); // yes, this is the proper width and height I tested it
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, _msaa_renderbuffer);
    }

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE) {
        NSLog(@"Failed to make complete framebuffer object %x", status);
        exit(1);
    }
}

在我的 ViewController 上调用 viewDidLoad 后，我在我的 UIView 子类上调用方法 setupDisplayLink。

- (void)setupDisplayLink {
    CADisplayLink* displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(render:)];
    //displayLink.frameInterval = [[NSNumber numberWithInt:1] integerValue];
    [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
}

这调用了我的渲染方法，非常简单:

- (void)render:(CADisplayLink*)displayLink {
    glBindRenderbuffer(GL_RENDERBUFFER, _msaa_framebuffer);

    glViewport(0, 0, [AppDelegate screenWidth], [AppDelegate screenHeight]);
    glClearColor(188.0f / 255.0f, 226.0f / 255.0f, 232.0f / 255.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    [[OpenGLViewController instance].menu draw:displayLink]; // drawing happens here

    glBindFramebuffer(GL_DRAW_FRAMEBUFFER_APPLE, _framebuffer);
    glBindFramebuffer(GL_READ_FRAMEBUFFER_APPLE, _msaa_framebuffer);

    glResolveMultisampleFramebufferAPPLE();

    glDiscardFramebufferEXT(GL_READ_FRAMEBUFFER_APPLE, 1, (GLenum[1]) { GL_COLOR_ATTACHMENT0 });

    glBindRenderbuffer(GL_RENDERBUFFER, _renderbuffer);

    NSLog(@"%@", @"HI");
    [_context presentRenderbuffer:GL_RENDERBUFFER];
}

它根本没有挂起(应用程序一直在控制台中打印“HI”，因为我在渲染方法中告诉它)。出于某种原因，当我为多重采样添加额外的帧缓冲区和渲染缓冲区时，只绘制了第一帧，我不知道为什么。它只是卡住在那个框架上。为什么我的应用程序只能使用 MSAA 绘制第一帧？

Answer 1

至少可以说，这并不奇怪。唯一一次将 _msaa_framebuffer 绑定(bind)为 DRAW 缓冲区是在初始化 FBO 后立即进行。

第一次调用 render (...) 时，将以下行绘制到您的 _msaa_framebuffer 中:

[[OpenGLViewController instance].menu draw:displayLink]; // drawing happens here

但是，稍后在 render (...) 中，您将绘制缓冲区设置为 _framebuffer 并且从那时起您再也不会更改它。

要解决您的问题，您所要做的就是记住在 render (...) 函数开头将 _msaa_framebuffer 绑定(bind)为绘制缓冲区:

- (void)render:(CADisplayLink*)displayLink {
  glBindFramebuffer(GL_DRAW_FRAMEBUFFER_APPLE, _msaa_framebuffer);