這個操作看了看介紹是為了減少正向渲染（就是一個模型完了再渲染下一個）的開銷

介紹

正向渲染(Forward Rendering)或者正向著色法(Forward Shading)，在場景中我們根據所有光源照亮一個物體，之後再渲染下一個物體，以此類推。它非常容易理解，也很容易實現，但是同時它對程式效能的影響也很大，因為對於每一個需要渲染的物體，程式都要對每一個光源每一個需要渲染的片段進行迭代，這是非常多的

延遲著色法基於我們延遲(Defer)或推遲(Postpone)大部分計算量非常大的渲染(像是光照)到後期進行處理的想法。它包含兩個處理階段(Pass)：在第一個幾何處理階段(Geometry Pass)中，我們先渲染場景一次，之後獲取物件的各種幾何資訊，並儲存在一系列叫做G緩衝(G-buffer)的紋理中；想想位置向量(Position Vector)、顏色向量(Color Vector)、法向量(Normal Vector)和/或鏡面值(Specular Value)。場景中這些儲存在G緩衝中的幾何資訊將會在之後用來做(更復雜的)光照計算。

會有一個G-Buffer 先用來儲存position normal albedo specular  

第二次操作 就有點像後期了 處理的是quad

GLuint gBuffer;
    glGenFramebuffers(1, &gBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, gBuffer);
    GLuint gPosition, gNormal, gAlbedoSpec;
    // - Position color buffer
    glGenTextures(1, &gPosition);
    glBindTexture(GL_TEXTURE_2D, gPosition);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, gPosition, 0);
    // - Normal color buffer
    glGenTextures(1, &gNormal);
    glBindTexture(GL_TEXTURE_2D, gNormal);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_FLOAT, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, gNormal, 0);
    // - Color + Specular color buffer
    glGenTextures(1, &gAlbedoSpec);
    glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT2, GL_TEXTURE_2D, gAlbedoSpec, 0);
    // - Tell OpenGL which color attachments we'll use (of this framebuffer) for rendering 
    GLuint attachments[3] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2 };
    glDrawBuffers(3, attachments);
    // - Create and attach depth buffer (renderbuffer)
    GLuint rboDepth;
    glGenRenderbuffers(1, &rboDepth);
    glBindRenderbuffer(GL_RENDERBUFFER, rboDepth);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rboDepth);
    // - Finally check if framebuffer is complete
    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        std::cout << "Framebuffer not complete!" << std::endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
 

第一次看見這個glDrawBuffers  不過看語義就是要把這三個attachment繪製了吧

//vertex
#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;
layout (location = 2) in vec2 texCoords;

out vec3 FragPos;
out vec2 TexCoords;
out vec3 Normal;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
    vec4 worldPos = model * vec4(position, 1.0f);
    FragPos = worldPos.xyz; 
    gl_Position = projection * view * worldPos;
    TexCoords = texCoords;
    
    mat3 normalMatrix = transpose(inverse(mat3(model)));
    Normal = normalMatrix * normal;
}
//fragment
#version 330 core
layout (location = 0) out vec3 gPosition;
layout (location = 1) out vec3 gNormal;
layout (location = 2) out vec4 gAlbedoSpec;

in vec2 TexCoords;
in vec3 FragPos;
in vec3 Normal;

uniform sampler2D texture_diffuse1;
uniform sampler2D texture_specular1;

void main()
{    
    // Store the fragment position vector in the first gbuffer texture
    gPosition = FragPos;
    // Also store the per-fragment normals into the gbuffer
    gNormal = normalize(Normal);
    // And the diffuse per-fragment color
    gAlbedoSpec.rgb = texture(texture_diffuse1, TexCoords).rgb;
    // Store specular intensity in gAlbedoSpec's alpha component
    gAlbedoSpec.a = texture(texture_specular1, TexCoords).r;
}
 

這樣把位置和法線糾正一下 操作過後 position normal albedospec就存了該有的資訊 rbodepth存的深度 

然後就繪製quad

 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        shaderLightingPass.Use();
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, gPosition);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, gNormal);
        glActiveTexture(GL_TEXTURE2);
        glBindTexture(GL_TEXTURE_2D, gAlbedoSpec);
        // Also send light relevant uniforms
        for (GLuint i = 0; i < lightPositions.size(); i++)
        {
            glUniform3fv(glGetUniformLocation(shaderLightingPass.Program, ("lights[" + std::to_string(i) + "].Position").c_str()), 1, &lightPositions[i][0]);
            glUniform3fv(glGetUniformLocation(shaderLightingPass.Program, ("lights[" + std::to_string(i) + "].Color").c_str()), 1, &lightColors[i][0]);
            // Update attenuation parameters and calculate radius
            const GLfloat constant = 1.0; // Note that we don't send this to the shader, we assume it is always 1.0 (in our case)
            const GLfloat linear = 0.7;
            const GLfloat quadratic = 1.8;
            glUniform1f(glGetUniformLocation(shaderLightingPass.Program, ("lights[" + std::to_string(i) + "].Linear").c_str()), linear);
            glUniform1f(glGetUniformLocation(shaderLightingPass.Program, ("lights[" + std::to_string(i) + "].Quadratic").c_str()), quadratic);
        }
        glUniform3fv(glGetUniformLocation(shaderLightingPass.Program, "viewPos"), 1, &camera.Position[0]);
        // Finally render quad
        RenderQuad();

用於計算的資料都已經在紋理的rgba裡面 vec4 value=texture2D(uv,texture)就拿到了。

//vertex
#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec2 texCoords;

out vec2 TexCoords;

void main()
{
    gl_Position = vec4(position, 1.0f);
    TexCoords = texCoords;
}
//fragment
#version 330 core
out vec4 FragColor;
in vec2 TexCoords;

uniform sampler2D gPosition;
uniform sampler2D gNormal;
uniform sampler2D gAlbedoSpec;

struct Light {
    vec3 Position;
    vec3 Color;
    
    float Linear;
    float Quadratic;
};
const int NR_LIGHTS = 32;
uniform Light lights[NR_LIGHTS];
uniform vec3 viewPos;

void main()
{             
    // Retrieve data from gbuffer
    vec3 FragPos = texture(gPosition, TexCoords).rgb;
    vec3 Normal = texture(gNormal, TexCoords).rgb;
    vec3 Diffuse = texture(gAlbedoSpec, TexCoords).rgb;
    float Specular = texture(gAlbedoSpec, TexCoords).a;
    
    // Then calculate lighting as usual
    vec3 lighting  = Diffuse * 0.1; // hard-coded ambient component
    vec3 viewDir  = normalize(viewPos - FragPos);
    for(int i = 0; i < NR_LIGHTS; ++i)
    {
        // Diffuse
        vec3 lightDir = normalize(lights[i].Position - FragPos);
        vec3 diffuse = max(dot(Normal, lightDir), 0.0) * Diffuse * lights[i].Color;
        // Specular
        vec3 halfwayDir = normalize(lightDir + viewDir);  
        float spec = pow(max(dot(Normal, halfwayDir), 0.0), 16.0);
        vec3 specular = lights[i].Color * spec * Specular;
        // Attenuation
        float distance = length(lights[i].Position - FragPos);
        float attenuation = 1.0 / (1.0 + lights[i].Linear * distance + lights[i].Quadratic * distance * distance);
        diffuse *= attenuation;
        specular *= attenuation;
        lighting += diffuse + specular;
    }    
    FragColor = vec4(lighting, 1.0);
}

前面提取出那些資料，後面的計算就是phong光照計算了

到這裡 純 延遲渲染就完了 但是 還有正向和延遲混合啊

記得前面有個rboDepth嗎。。存了深度還沒用吶。

        RenderQuad();//之後
// 2.5. Copy content of geometry's depth buffer to default framebuffer's depth buffer
        glBindFramebuffer(GL_READ_FRAMEBUFFER, gBuffer);
        glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0); // Write to default framebuffer
        // blit to default framebuffer. Note that this may or may not work as the internal formats of both the FBO and default framebuffer have to match.
        // the internal formats are implementation defined. This works on all of my systems, but if it doesn't on yours you'll likely have to write to the 		
        // depth buffer in another shader stage (or somehow see to match the default framebuffer's internal format with the FBO's internal format).
        glBlitFramebuffer(0, 0, SCR_WIDTH, SCR_HEIGHT, 0, 0, SCR_WIDTH, SCR_HEIGHT, GL_DEPTH_BUFFER_BIT, GL_NEAREST);
        glBindFramebuffer(GL_FRAMEBUFFER, 0);

        // 3. Render lights on top of scene, by blitting
        shaderLightBox.Use();
        glUniformMatrix4fv(glGetUniformLocation(shaderLightBox.Program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
        glUniformMatrix4fv(glGetUniformLocation(shaderLightBox.Program, "view"), 1, GL_FALSE, glm::value_ptr(view));
        for (GLuint i = 0; i < lightPositions.size(); i++)
        {
            model = glm::mat4();
            model = glm::translate(model, lightPositions[i]);
            model = glm::scale(model, glm::vec3(0.25f));
            glUniformMatrix4fv(glGetUniformLocation(shaderLightBox.Program, "model"), 1, GL_FALSE, glm::value_ptr(model));
            glUniform3fv(glGetUniformLocation(shaderLightBox.Program, "lightColor"), 1, &lightColors[i][0]);
            RenderCube();
        }

glBlitFrameBuffer幾步就是把深度挪到渲染到螢幕上的操作 這樣 深度就不會有問題了 可以愉快的在最後繪製正向渲染的物體了

這個基於phong的。

這個是看learnopengl的學習記錄。

原文 https://learnopengl-cn.github.io/05%20Advanced%20Lighting/08%20Deferred%20Shading/