c++ - OpenGL:一次只能使用一个 FBO

Question

我正在尝试渲染到纹理，然后复制该纹理并通过后期处理运行它，然后将过滤后的图像与原始图像组合。我得到了它，所以我可以渲染到纹理，然后处理它并显示它，但我只能处理一次。我真的不确定出了什么问题。

这是我的 FBO 设置代码:

for (int i = 0; i < 3; i++) {
    glGenFramebuffers(1, &postfboId[i]);
    glGenTextures(1, &postTextureId[i]);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, postTextureId[i]);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    //float color[4] = {0.0, 0.0, 0.0, 1.0};
    //glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, color);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB, screenSize.x, screenSize.y, 0, GL_RGB, GL_UNSIGNED_BYTE, 0);

    // create a framebuffer object
    glBindFramebuffer(GL_FRAMEBUFFER, postfboId[i]);


    glGenRenderbuffers(1, &depthrenderbuffer[i]);
    glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer[i]);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, screenSize.x, screenSize.y);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer[i]);


    // attach the texture to FBO depth attachment point
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,GL_TEXTURE_2D, postTextureId[i], 0);

    }
    GLenum DrawBuffers[] = {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2};
    glDrawBuffers(1, DrawBuffers);
    // check FBO status
    FBOstatus = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(FBOstatus != GL_FRAMEBUFFER_COMPLETE)
        printf("hey man, you might want to sit down a minute, i didn't want to have to say this to you, but the FBO failed.\n");

我想也许我需要 glDrawBuffers 来制作 3 而不是 1，但这只会导致 FBO 不完整。这是我的渲染代码:

glBindFramebuffer(GL_FRAMEBUFFER,postfboId[0]);
sf::Vector2u size = screenSize;
changeSize(size.x, size.y);
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); 
//clear viewport
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glUseProgram(prog);

glPushMatrix();

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
setLookat();
glCullFace(GL_BACK);
setLights();
drawObjs();

glPopMatrix();

//first round post process
glClearColor(0, 0, 0, 1);
glUseProgram(postProg);

glBindFramebuffer(GL_FRAMEBUFFER,postfboId[1]);
glUniform1i(postProcessMode, 1);
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glPushMatrix();
glLoadIdentity();
glOrtho(0,screenSize.x,0,screenSize.y,-1,20);
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glPushMatrix();
glLoadIdentity();
glColor4f(1,1,1,1);
glUniform1i(texUniform3, 0);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D,postTextureId[0]);
glEnable(GL_TEXTURE_2D);
glTranslated(0,0,-19.5);
glBegin(GL_QUADS);
glTexCoord2d(0,0);glVertex3f(0,0,0);
glTexCoord2d(1,0);glVertex3f(screenSize.x,0,0);
glTexCoord2d(1,1);glVertex3f(screenSize.x,screenSize.y,0);
glTexCoord2d(0,1);glVertex3f(0,screenSize.y,0);
glEnd();


// round 2 post
glUniform1i(postProcessMode, 2);
glBindFramebuffer(GL_FRAMEBUFFER,0);

glUniform1i(texUniform3, 3);
glActiveTexture(GL_TEXTURE3);
// bind postTextureId[0] to draw real screen.
glBindTexture(GL_TEXTURE_2D,postTextureId[1]);
glEnable(GL_TEXTURE_2D);
glTranslated(0,0,0.5);
glBegin(GL_QUADS);
glTexCoord2d(0,0);glVertex3f(0,0,0);
glTexCoord2d(1,0);glVertex3f(screenSize.x,0,0);
glTexCoord2d(1,1);glVertex3f(screenSize.x,screenSize.y,0);
glTexCoord2d(0,1);glVertex3f(0,screenSize.y,0);
glEnd();
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();

无论出于何种原因，将一个 FBO 纹理绘制到另一个 FBO 会导致无意义，但是将该 FBO 纹理绘制到屏幕上是可以的。此外，所有 3 个 FBO 都可以工作，只是不是同时工作，这很奇怪，因为我有另一个 FBO，它只有一个用于阴影贴图的深度缓冲区，可以正确显示。

Answer 1

一个显而易见的问题是您缺少对除第一个渲染目标之外的所有渲染目标的 glClear() 调用。绑定(bind) fbo 0 后调用一次:

glBindFramebuffer(GL_FRAMEBUFFER,postfboId[0]);
...
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

但是绑定(bind)fbo 1后还需要清除:

glBindFramebuffer(GL_FRAMEBUFFER,postfboId[1]);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

绑定(bind)默认帧缓冲区后:

glBindFramebuffer(GL_FRAMEBUFFER,0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

您的一些 glPushMatrix() 和 glPopMatrix() 调用看起来也有些可疑。但是如果不看整个代码就很难判断它们是否不正确。您可能需要仔细检查它们是否全部平衡，以及您在调用它们时是否处于正确的矩阵模式。例如在这个序列中:

glMatrixMode(GL_PROJECTION);
glPopMatrix();
glPushMatrix();
glLoadIdentity();

glPopMatrix() 和 glPushMatrix() 调用是多余的。如果有的话，它们可能是有害的，因为如果您之前没有调用 glPushMatrix() 就会出错。否则，它会先将之前的矩阵复制到顶部条目，然后立即用单位矩阵覆盖它。这与单独调用 glLoadIdentity() 是一样的。