opengl - OpenGL glReadPixels 得到 1282 错误

Question

我想用 OpenGL 创建一个屏幕外渲染器。

我创建了 aFBO和 aRBO来调用glReadPixels()，但总是出错。

这是我的代码：

// Init
GLuint fbo;
GLuint rbo;

glGenFramebuffers(1, &fbo);

glGenRenderbuffers(1, &rbo);
glBindRenderbuffer(GL_RENDERBUFFER, rbo);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8, width, height);

glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rbo);

glClearColor(0.0f, 1.0f, 1.0f, 1.0f);

// Render loop
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);

...

std::vector<unsigned char> output(width * height * 4);
glReadBuffer(GL_COLOR_ATTACHMENT0);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, &output[0]);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);

// Deinit
glDeleteRenderbuffers(1, &rbp);
glDeleteFramebuffers(1, &fbo);

输出不包含任何内容，并且glGetError()函数总是1282 (GL_INVALID_OPERATION)在调用glReadPixels().

这段代码有什么问题？