OpenGL：读取帧缓冲区的深度纹理

Question

我在Java中使用LWJGL，它具有与C++ OpenGL相同的函数名称。请注意，我不得不使用OpenGL的“旧”固定功能管线。

//the initialization method 
public void init(int width, int height) { 
    //initializing the PBO 
    pbo_id = glGenBuffers(); 
    // [...] 

    //initializing the Framebuffer 
    framebufferObject = glGenFramebuffers(); 
    framebufferTexture = glGenTextures(); 

    depthBuffer = glGenRenderbuffers(); 

    framebufferFilter = GL_NEAREST; 

    glBindTexture(GL_TEXTURE_2D, framebufferTexture); 

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); 
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); 
    glTexParameterf(GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_T, GL_CLAMP); 

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, (ByteBuffer)null); 
    glBindFramebuffer(GL_FRAMEBUFFER, framebufferObject); 
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, framebufferTexture, 0); 

    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, width, height); 
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthBuffer); 

    glBindTexture(GL_TEXTURE_2D, 0); 
} 

//this is called after the world was rendered to the framebuffer 
public void capture() { 
    //binding the PBO 
    glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo_id); 

    //binding the Framebuffer's texture 
    glBindTexture(GL_TEXTURE_2D, framebuffer_id); 

    //storing the Framebuffer's contents in the PBO 
    glGetTexImage(GL_TEXTURE_2D, 0, GL_RGB, GL_UNSIGNED_BYTE, 0); 

    //unbinding the Framebuffer 
    glBindTexture(GL_TEXTURE_2D, 0); 

    //unbinding the PBO 
    glBindBuffer(GL_PIXEL_PACK_BUFFER, 0); 
} 

我怎么会深度图的内容（我想被初始化为深度缓存）存储在：

我目前正在成功地使用下面的代码绘制帧缓冲区的RGB内容PixelBufferObjects PBO而不是“主”帧缓冲区内容？

UPDATE： 这是我使用的阅读深度图的内容，现在PBO该代码：

public void captureDepthMap() { 
    //binding the PBO 
    glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo_id); 

    glPixelStorei(GL_PACK_ALIGNMENT, 1); 
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1); 

    //binding the FBO 
    glBindFramebuffer(GL_FRAMEBUFFER, framebufferObject); 

    //storing the Depth Map's contents in the PBO 
    glReadPixels(0, 0, width, height, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT_24_8, 0); 

    //unbinding the FBO 
    glBindFramebuffer(GL_FRAMEBUFFER, 0); 

    //unbinding the PBO 
    glBindBuffer(GL_PIXEL_PACK_BUFFER, 0); 
} 

产生的图像仅仅是黑色的但是。 这可能是什么原因造成的？我可能搞砸了一些GL格式吗？

Answer 1

绑定“framebuffer的纹理”并没有什么意义。此纹理仅表示一个（颜色缓冲区）附件。您可以将多个纹理附加到帧缓冲区，深度缓冲区也可以作为纹理进行存储。

如果您使用深度纹理附件而不是渲染缓冲区，则可以按照读取颜色附件的相同方式进行读取。唯一的区别是格式和数据类型：GL_DEPTH_COMPONENT和GL_UNSIGNED_INT_24_8。

或者，您可以使用glReadPixels (...)从附加的渲染缓冲区读取。由于您必须指定一个矩形才能读取，因此API涉及更多一点。