将深度渲染为从帧缓冲区到显示窗口的纹理

问题描述

我是 OpenGL 的新手。我想使用帧缓冲区读取并保存渲染场景中的所有深度值。我设法将其设置为附加到深度组件的帧缓冲区。但是当我将深度纹理渲染到默认帧缓冲区（显示窗口）时，它只显示白色，即使我对深度值进行了线性化（教程来自 https://learnopengl.com/）。当我从默认帧缓冲区片段着色器中的 gl_FragCoord.z 访问深度值时，我得到了一个深度图，并且绘图也正常，但是当将深度作为纹理从单独的帧缓冲区发送到默认值时，深度图像是强烈的白色。

我为此编写的代码如下：

自定义帧缓冲顶点和片段着色器

const char* vertexShaderFBO =
        "#version 330\n"
        "layout (location = 0)  in vec3 vp;"
        "uniform mat4 camera;"
        "uniform mat4 projection;"
        "void main() {"
        "  gl_Position = camera * projection * vec4(vp.x,vp.y,vp.z,1.0);"
        "}";

const char* fragmentShaderFBO =
        "#version 330\n"
        "layout (location = 0) out float frag_depth;"
        "float near = 0.1;"
        "float far = 100;"
        "float LinearizeDepth(float depth)"
        "{"
        "    float z = depth * 2.0 - 1.0;"
        "   return (2.0 * near * far) / (far + near - z * (far - near));"
        "}"
        "void main() {"
        "  float linearDepth = LinearizeDepth(gl_FragCoord.z) / far;" // divided by far is just to visualize depth
        "  frag_depth = linearDepth ;"
        "}";

默认帧缓冲顶点和片段着色器

const char* vertexShader =
        "#version 330\n"
        "layout (location = 0)  in vec3 vp;"
        "uniform mat4 camera;"
        "uniform mat4 projection;"
        "void main() {"
        "  gl_Position =  camera * projection * vec4(vp.x,1.0);"
        "}";

const char* fragmentShader =
        "#version 330\n"
        "out vec4 frag_colour;"
        "uniform sampler2D depthSampler;"
        "in vec2 texCoords;"
        "void main() {"
        "  float depthVal = texture(depthSampler,texCoords).r;"
        "  frag_colour = vec4(vec3(depthVal),1);"
        "}";

深度纹理

gluint setDepthTexture()
{
    gluint texture;
    glGenTextures(1,&texture);
    glBindTexture(GL_TEXTURE_2D,texture);

    glTexImage2D(GL_TEXTURE_2D,GL_DEPTH_COMPONENT,SCREEN_SIZE.x,SCREEN_SIZE.y,GL_FLOAT,0);

    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_CLAMP_TO_EDGE);
    glTexParameteri (GL_TEXTURE_2D,GL_TEXTURE_COMPARE_MODE,GL_NONE);

    return texture;
}

渲染关闭文件

int renderOFF(Vertices* vertices,Faces* faces,Views* views)
{
    // initializaion
    ... 
    ...
    glEnable(GL_DEPTH_TEST); // enable depth buffer
    glDepthFunc(GL_LESS); // If pixel closer to camera then overwrite the existing pixel

    ...
    ...

    // create framebuffer shader
    gluint shaderProgramFBO = createShader(vertexShaderFBO,fragmentShaderFBO);

    // create renderer shader
    gluint shaderProgram = createShader(vertexShader,fragmentShader);

    //set texture
    gluint depthTexture = setDepthTexture();

    // set framebuffer
    unsigned int fbo;
    glGenFramebuffers(1,&fbo);
    glBindFramebuffer(GL_FRAMEBUFFER,fbo);

    // attach texture to framebuffer
    glFramebufferTexture2D(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,GL_TEXTURE_2D,depthTexture,0);

    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    {
        std::cout << "Failed to bind framebuffer" << std::endl;
        return -1;
    }

     // Use no color attachment
    glDrawBuffer(GL_NONE);
    glreadBuffer(GL_NONE);
    glBindFramebuffer(GL_FRAMEBUFFER,0);

    gluseProgram(shaderProgram);
    gluniform1i(glGetUniformlocation(shaderProgram,"depthSampler"),0);

    // set camera
    ...
    ...

    while(!glfwWindowShouldClose(glfWwindow))
    {
        // check OpenGL error
        GLenum err;
        while ((err = glGetError()) != GL_NO_ERROR) {
            std::cout << "OpenGL error: " << err << std::endl;
        }


        // bind to custom framebuffer
        glBindFramebuffer(GL_FRAMEBUFFER,fbo);

        glClearColor(0,1); // clear screen to black
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        gluseProgram(shaderProgramFBO);
        ...

        glEnable(GL_DEPTH_TEST);

        glBindVertexArray(vao);
        glDrawElements(GL_TRIANGLES,faces->size,GL_UNSIGNED_INT,0);

        glBindFramebuffer(GL_FRAMEBUFFER,0);

        // default framebuffer
        glClearColor(0,1); // clear screen to black
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        processKeyBoardInput(glfWwindow);

        ...

        //gldisable(GL_DEPTH_TEST);
        glBindVertexArray(vao);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D,depthTexture);
        glDrawElements(GL_TRIANGLES,0);

        glfwSwapBuffers(glfWwindow);
        glfwPollEvents();

        sleep(1);
    }

    glDeleteFramebuffers(1,&fbo);
    glDeleteVertexArrays(1,&vao);
    glDeleteBuffers(1,&vbo);

    glfwTerminate();
    return 0;
}

生成的渲染图像与预期的图像结果如下所示

解决方法

片段着色器将 [near,far] 范围内的深度值分配给 [0.0,1.0] 范围内的颜色值。如果所有几何体都在接近 0.0 的区域中，则渲染将显示为几乎黑色，因为 0.1 渲染为黑色，100 渲染为白色。将视点 (viewing frustum) 的近平面和远平面尽可能靠近几何体，以利用 0.0 和 1.0 之间的整个范围。

当近平面接近 0 时，您的片段着色器会正常工作。随着近平面变大，您应该使用：

~~float linearDepth = LinearizeDepth(gl_FragCoord.z) / far;~~

float linearDepth = (LinearizeDepth(gl_FragCoord.z) - near) / (far - near);

depth-buffer framebuffer opengl opengl opengl textures