ios - OpenGL 中的离屏帧缓冲区

Question

我正在使用 OpenGL 创建一个 iPhone 游戏，我想在屏幕外帧缓冲区上绘图，然后将该帧缓冲区用作在实际屏幕上绘图的纹理。我的代码基于 Apple's和 GLSprite 示例，但似乎我在切换绘图目标时做得不对，因为我只得到一个空白纹理。我正在使用的代码如下。怎么了？即时渲染纹理的最佳方式是什么？

下面的 Creating an Offscreen Framebuffer 给出了 8cd6 错误代码。

创建屏幕帧缓冲区

glGenFramebuffersOES(1, &viewFramebuffer);
glGenRenderbuffersOES(1, &viewRenderbuffer);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(id<EAGLDrawable>)self.layer];
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, viewRenderbuffer);

glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);

if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES) {
    NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES));
    return NO;
}

创建离屏帧缓冲区

glGenFramebuffers(1, &offscreenFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, offscreenFramebuffer);

glGenTextures(1,&framebufferTexture);
glBindTexture(GL_TEXTURE_2D, framebufferTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 64, 64, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, framebufferTexture, 0);

GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if(status != GL_FRAMEBUFFER_COMPLETE) {
    NSLog(@"ERROR: %x", status);
}

绘图，循环:

glBindTexture(GL_TEXTURE_2D,textureFromFile); //Switch to a texture from a file
glBindFramebufferOES(GL_FRAMEBUFFER_OES, offscreenFramebuffer); //Switch to the offscreen framebuffer
//Render the texture to be used later
glBindTexture(GL_TEXTURE_2D,framebufferTexture); //Switch to the offscreen framebuffer's texture
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); //Switch to the screen framebuffer
//Do the drawing using the texture rendered just before, and present this to the screen.

glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];

Answer 1

问题很简单:您忘记了在屏幕 上绘图。你知道，默认帧缓冲区，当你执行 glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0); 时你得到的是你在编写这段代码之前渲染得很好的东西。

没有所谓的“屏幕上”帧缓冲区对象。根据定义，所有用户定义的 FBO 都是屏幕外的。

你根本不应该有这个 viewFramebuffer FBO。相反，您应该绘制到您的纹理，然后使用该纹理绘制到默认帧缓冲区。