Question

我想使用可编程管道（使用glsl）进行体积渲染，并且没有固定的管道。我使用2个着色器程序exitPointProg和rayCastProg实现了2次传递。第一遍是获得立方体边界框的出口点（即背面），该边界框将用作进行光线投射的下一遍中的纹理。进行光线投射体绘制的想法来自here。我认为我已经完成了大部分工作，因为我已经使用固定管道和可编程管道实现了这一点。让我感到困惑的是我用第一帧获得了结果，然后用闪光灯将屏幕上的显示变为白色（我设置glClearColor(1.0f, 1.0f, 1.0f, 1.0f)。我认为切换时可能有些错误着色器程序或FBO。这是我在render（）函数中所做的。

第一遍，使用着色器程序exitPoints渲染到绑定了exitPointProg纹理的fbo以获取立方体边界框的出口点。

2ed pass，将exitPoints纹理（绑定到GL_TEXTURE1）映射到着色器程序rayCastProg，作为将在着色器中使用的统一sampler2D变量。这是setupFBO和render以及两个子程序： setupFBO()函数：

void SimpleRayCasting::setupFBO()
{
    GLuint textureHandles[1];
    glGenTextures(1, textureHandles);
    entryPoints = textureHandles[0];


    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, exitPoints);
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
    glTexImage2D(GL_TEXTURE_2D, 0,GL_RGBA16F, width, height, 0, GL_RGBA, GL_FLOAT, NULL);


    GLuint depthRenderBuffer;
    glGenRenderbuffers(1, &depthRenderBuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, depthRenderBuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, width, height);

    glGenFramebuffers(1, &frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, 
                    exitPoints, 0/* level */);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, 
                    depthRenderBuffer);


    checkFramebufferState(__FILE__, __LINE__);
    GLenum drawbufs[] = {GL_COLOR_ATTACHMENT0};
    glDrawBuffers(1, drawbufs);
    glBindFramebuffer(GL_FRAMEBUFFER,0);
}

render()函数：

void SimpleRayCasting::render()
{
    getExitPoints();
    GLUtils::checkForOpenGLError(__FILE__,__LINE__);
    rayCasting();
    GLUtils::checkForOpenGLError(__FILE__,__LINE__);
}

getExitPoints()函数：

void SimpleRayCasting::getExitPoints() 
{
    // render to the texture
    glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
    glEnable(GL_DEPTH_TEST);
    glViewport(0, 0, width, height);
    // checkFramebufferState(__FILE__, __LINE__); 
    glClearColor(0.2f, 0.2f, 0.2f, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    exitPointsProg.use();
    // note that the model will recalculated.
    model = mat4(1.0f);
    model *= glm::rotate(angle , vec3(0.0f,1.0f,0.0f));
    model *= glm::rotate(90.0f, vec3(1.0f, 0.0f, 0.0f));
    model *= glm::translate(vec3(-0.5f, -0.5f, -0.5f));
    view = glm::lookAt(vec3(0.0f,0.0f,2.0f), vec3(0.0f,0.0f,0.0f), vec3(0.0f,1.0f,0.0f));
    projection = mat4(1.0f);
    projection = glm::perspective(60.0f, (float)width/(float)height,0.01f, 400.0f);   
    setMatrices(exitPointsProg);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_FRONT);
    drawBoundBox();
    glDisable(GL_CULL_FACE);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

rayCasting函数：

void SimpleRayCasting::rayCasting()
{
    // Directly render to the screen
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glEnable(GL_DEPTH_TEST);
    glViewport(0, 0, width, height);
    glClearColor(1.0f, 1.0f, 1.0f, 1.0);
    glClear(GL_COLOR_BUFFER_BIT |  GL_DEPTH_BUFFER_BIT);
    rayCastProg.use();
    model = mat4(1.0f);
    model *= glm::rotate(angle, vec3(0.0f,1.0f,0.0f));
    model *= glm::rotate(90.0f, vec3(1.0f, 0.0f, 0.0f));
    model *= glm::translate(vec3(-0.5f, -0.5f, -0.5f));
    view = glm::lookAt(vec3(0.0f,0.0f,2.0f), vec3(0.0f,0.0f,0.0f), vec3(0.0f,1.0f,0.0f));
    projection = mat4(1.0f);
    projection = glm::perspective(60.0f, (float)width/(float)height,0.01f, 400.0f);   
    setMatrices(rayCastProg);
    rayCastProg.setUniform("StepSize", stepSize);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, exitPoints);
    rayCastProg.setUniform("ExitPoints", 1);
    glActiveTexture(GL_TEXTURE4);
    glBindTexture(GL_TEXTURE_3D, volume_to);
    rayCastProg.setUniform("VolumeTex", 4);
    glActiveTexture(GL_TEXTURE5);
    glBindTexture(GL_TEXTURE_1D, transferFunc_to);
    rayCastProg.setUniform("TransferFunc", 5);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    drawBoundBox();
    glDisable(GL_CULL_FACE);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
}

我在Qt中使用从QGLWidget继承的类。正如我早些时候提到的那样，我在第一帧时得到了正确的结果，很快它就会闪现并变成白色。我不知道这有什么问题，着色器程序或FBO事件的切换是否有问题？我一直在研究这个问题，无法弄明白，任何帮助都将不胜感激！

编辑询问 是否有任何演示或教程演示如何在FBO中使用多个glsl着色器程序？

如何在glsl中切换着色器程序

0 个答案: