(十三)MipMap

MipMap概念

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滤波

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采样

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mipmap级别判定

问题：opengl如何判定应该使用下一级的mipmap呢？
通过glsl中的求偏导函数计算变化量决定
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手动实现mipmap原理

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1、生成mipmap的各个级别
2、修改vertexShader使得三角形随着时间变小
**** 需要更改Filter才能够在变小的时候使用mipmap *****

#include <glad/glad.h>//glad必须在glfw头文件之前包含
#include <GLFW/glfw3.h>
#include <iostream>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
void frameBufferSizeCallbakc(GLFWwindow* window, int width, int height)
{glViewport(0, 0, width, height);
}
void glfwKeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
}GLuint program = 0;
GLuint vao = 0;
void prepareVAO()
{//positionsfloat positions[] = {-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f,0.0f,  0.5f, 0.0f,};//颜色float colors[] = {1.0f, 0.0f,0.0f,0.0f, 1.0f,0.0f,0.0f, 0.0f,1.0f,};//索引unsigned int indices[] = {0, 1, 2,};//uv坐标float uvs[] = {0.0f, 0.0f,1.0f, 0.0f,0.5f, 1.0f,};//2 VBO创建GLuint posVbo = 0;GLuint colorVbo = 0;GLuint uvVbo = 0;glGenBuffers(1, &posVbo);glBindBuffer(GL_ARRAY_BUFFER, posVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);glGenBuffers(1, &colorVbo);glBindBuffer(GL_ARRAY_BUFFER, colorVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);glGenBuffers(1, &uvVbo);glBindBuffer(GL_ARRAY_BUFFER, uvVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(uvs), uvs, GL_STATIC_DRAW);//3 EBO创建GLuint ebo = 0;glGenBuffers(1, &ebo);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);//4 VAO创建vao = 0;glGenVertexArrays(1, &vao);glBindVertexArray(vao);//5 绑定vbo ebo 加入属性描述信息//5.1 加入位置属性描述信息glBindBuffer(GL_ARRAY_BUFFER, posVbo);glEnableVertexAttribArray(0);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//5.2 加入颜色属性描述信息glBindBuffer(GL_ARRAY_BUFFER, colorVbo);glEnableVertexAttribArray(1);glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//5.3 加入uv属性描述数据glBindBuffer(GL_ARRAY_BUFFER, uvVbo);glEnableVertexAttribArray(2);glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);//5.2 加入ebo到当前的vaoglBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBindVertexArray(0);
}
void prepareShader() {//1 完成vs与fs的源代码，并且装入字符串const char* vertexShaderSource ="#version 330 core\n""layout (location = 0) in vec3 aPos;\n""layout (location = 1) in vec3 aColor;\n""layout (location = 2) in vec2 aUV;\n""out vec3 color;\n""out vec2 uv;\n""uniform float time;\n""void main()\n""{\n""   float scale = 1.0/time;\n""   vec3 sPos = aPos * scale;\n""   gl_Position = vec4(sPos, 1.0);\n""   color = aColor;\n""   uv = aUV;\n""}\0";const char* fragmentShaderSource ="#version 330 core\n""out vec4 FragColor;\n""in vec3 color;\n""in vec2 uv;\n""uniform sampler2D sampler;\n""void main()\n""{\n""  FragColor = texture(sampler, uv);\n""}\n\0";//2 创建Shader程序（vs、fs）GLuint vertex, fragment;vertex = glCreateShader(GL_VERTEX_SHADER);fragment = glCreateShader(GL_FRAGMENT_SHADER);//3 为shader程序输入shader代码glShaderSource(vertex, 1, &vertexShaderSource, NULL);glShaderSource(fragment, 1, &fragmentShaderSource, NULL);int success = 0;char infoLog[1024];//4 执行shader代码编译 glCompileShader(vertex);//检查vertex编译结果glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);if (!success) {glGetShaderInfoLog(vertex, 1024, NULL, infoLog);std::cout << "Error: SHADER COMPILE ERROR --VERTEX" << "\n" << infoLog << std::endl;}glCompileShader(fragment);//检查fragment编译结果glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);if (!success) {glGetShaderInfoLog(fragment, 1024, NULL, infoLog);std::cout << "Error: SHADER COMPILE ERROR --FRAGMENT" << "\n" << infoLog << std::endl;}//5 创建一个Program壳子program = glCreateProgram();//6 将vs与fs编译好的结果放到program这个壳子里glAttachShader(program, vertex);glAttachShader(program, fragment);//7 执行program的链接操作，形成最终可执行shader程序glLinkProgram(program);//检查链接错误glGetProgramiv(program, GL_LINK_STATUS, &success);if (!success) {glGetProgramInfoLog(program, 1024, NULL, infoLog);std::cout << "Error: SHADER LINK ERROR " << "\n" << infoLog << std::endl;}//清理glDeleteShader(vertex);glDeleteShader(fragment);
}
GLuint genTexture(const char* picPath, int unitTexturt)
{//1 stbImage 读取图片int width, height, channels;//--反转y轴stbi_set_flip_vertically_on_load(true);unsigned char* data = stbi_load(picPath, &width, &height, &channels, STBI_rgb_alpha);//2 生成纹理并且激活单元绑定GLuint texture = 0;glGenTextures(1, &texture);//--激活纹理单元--glActiveTexture(GL_TEXTURE0 + unitTexturt);//--绑定纹理对象--glBindTexture(GL_TEXTURE_2D, texture);int tmepWidth = width, tempHeight = height;//3 传输纹理数据,开辟显存//glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);//遍历每个mipmap的层级，为每个级别的mipmap填充图片数据for (int level = 0; true; ++level){//1 将当前级别的mipmap对应的数据发往gpu端glTexImage2D(GL_TEXTURE_2D, level, GL_RGBA, tmepWidth, tempHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);//2 判断是否退出循环if (tmepWidth == 1 && tempHeight == 1)break;//3 计算下一次循环的宽度/高度，除以2tmepWidth = tmepWidth > 1 ? tmepWidth / 2 : 1;tempHeight = tempHeight > 1 ? tempHeight / 2 : 1;}//***释放数据stbi_image_free(data);//4 设置纹理的过滤方式glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);//*****重要*****////GL_NEAREST:在单个mipmap上采用最邻近采样//GL_LINEAR   //MIPMAP_LINEAR：在两层mipmap之间采用线性插值//MIPMAP_NEARESTglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);//5 设置纹理的包裹方式glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);//uglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);//vreturn texture;
}
void prepareTextrue()
{//GLuint grassTexture = genTexture("grass.jpg", 0);//GLuint landTexture = genTexture("land.jpg", 1);//GLuint noiseTexture = genTexture("noise.jpg", 2);GLuint wallTexture = genTexture("goku.jpg", 0);
}void render()
{//执行opengl画布清理操作glClear(GL_COLOR_BUFFER_BIT);//1.绑定当前的programglUseProgram(program);//2 更新Uniform的时候，一定要先UserProgram//2.1 通过名称拿到Uniform变量的位置Location//2.2 通过Location更新Uniform变量的值GLint time = glGetUniformLocation(program, "time");int i = glfwGetTime();glUniform1f(time, glfwGetTime());GLint sampler = glGetUniformLocation(program, "sampler");glUniform1i(sampler, 0);//3 绑定当前的vaoglBindVertexArray(vao);//4 发出绘制指令//glDrawArrays(GL_TRIANGLE_STRIP, 0, 6);glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);
}int main()
{//初始化glfw环境glfwInit();//设置opengl主版本号glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);//设置opengl次版本号glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);//设置opengl启用核心模式glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//创建窗体对象GLFWwindow* window = glfwCreateWindow(800, 600, "lenarnOpenGL", nullptr, nullptr);//设置当前窗体对象为opengl的绘制舞台glfwMakeContextCurrent(window);//窗体大小回调glfwSetFramebufferSizeCallback(window, frameBufferSizeCallbakc);//键盘相应回调glfwSetKeyCallback(window, glfwKeyCallback);//使用glad加载所有当前版本opengl的函数if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "初始化glad失败" << std::endl;return -1;};//设置opengl视口大小和清理颜色glViewport(0, 0, 800, 600);glClearColor(0.2f, 0.3f, 0.3f, 1.0f);//shaderprepareShader();//vaoprepareVAO();//textureprepareTextrue();//执行窗体循环while (!glfwWindowShouldClose(window)){//接受并分发窗体消息//检查消息队列是否有需要处理的鼠标、键盘等消息//如果有的话就将消息批量处理，清空队列glfwPollEvents();//渲染操作render();//切换双缓存glfwSwapBuffers(window);}//推出程序前做相关清理glfwTerminate();return 0;
}

上述代码即可实现随着时间的变化，不同层级的图片贴到三角形中的效果。
还可以不在代码中设置层级间的采样方式即注释掉

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);

在fs中，实现根据像素对应图素的数量多少，决定采样哪个层级的mipmap

#version 330 core
out vec4 FragColor;
in vec3 color;
in vec2 uv;
uniform sampler2D sampler;
uniform float width;
uniform float height;
void main()
{//FragColor = texture(sampler, uv);//1 获取当前像素对应的纹理上的纹素具体位置vec2 location = uv * vec2(width, height);//2 计算当前像素对应纹素具体位置在xy方向上的变化量vec2 dx = dFdx(location);vec2 dy = dFdy(location);//3 选择最大的delta，求log2（delta）float maxDelta = sqrt(max(dot(dx, dx), dot(dy,dy)));float L = log2(maxDelta);//4 计算出mipmap的采样级别int level = max(int(L + 0.5), 0);FragColor = textureLod(sampler, uv, level);
}

fs的glsl设置以上字符串，渲染时设置图片的宽度和高度即可达到同样的效果。

opengl自动生成mipmap

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#include <glad/glad.h>//glad必须在glfw头文件之前包含
#include <GLFW/glfw3.h>
#include <iostream>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
void frameBufferSizeCallbakc(GLFWwindow* window, int width, int height)
{glViewport(0, 0, width, height);
}
void glfwKeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
}GLuint program = 0;
GLuint vao = 0;
void prepareVAO()
{//positionsfloat positions[] = {-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f,0.0f,  0.5f, 0.0f,};//颜色float colors[] = {1.0f, 0.0f,0.0f,0.0f, 1.0f,0.0f,0.0f, 0.0f,1.0f,};//索引unsigned int indices[] = {0, 1, 2,};//uv坐标float uvs[] = {0.0f, 0.0f,1.0f, 0.0f,0.5f, 1.0f,};//2 VBO创建GLuint posVbo = 0;GLuint colorVbo = 0;GLuint uvVbo = 0;glGenBuffers(1, &posVbo);glBindBuffer(GL_ARRAY_BUFFER, posVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);glGenBuffers(1, &colorVbo);glBindBuffer(GL_ARRAY_BUFFER, colorVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);glGenBuffers(1, &uvVbo);glBindBuffer(GL_ARRAY_BUFFER, uvVbo);glBufferData(GL_ARRAY_BUFFER, sizeof(uvs), uvs, GL_STATIC_DRAW);//3 EBO创建GLuint ebo = 0;glGenBuffers(1, &ebo);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);//4 VAO创建vao = 0;glGenVertexArrays(1, &vao);glBindVertexArray(vao);//5 绑定vbo ebo 加入属性描述信息//5.1 加入位置属性描述信息glBindBuffer(GL_ARRAY_BUFFER, posVbo);glEnableVertexAttribArray(0);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//5.2 加入颜色属性描述信息glBindBuffer(GL_ARRAY_BUFFER, colorVbo);glEnableVertexAttribArray(1);glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//5.3 加入uv属性描述数据glBindBuffer(GL_ARRAY_BUFFER, uvVbo);glEnableVertexAttribArray(2);glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);//5.2 加入ebo到当前的vaoglBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBindVertexArray(0);
}
void prepareShader() {//1 完成vs与fs的源代码，并且装入字符串const char* vertexShaderSource ="#version 330 core\n""layout (location = 0) in vec3 aPos;\n""layout (location = 1) in vec3 aColor;\n""layout (location = 2) in vec2 aUV;\n""out vec3 color;\n""out vec2 uv;\n""uniform float time;\n""void main()\n""{\n""   float scale = 1.0/time;\n""   vec3 sPos = aPos * scale;\n""   gl_Position = vec4(sPos, 1.0);\n""   color = aColor;\n""   uv = aUV;\n""}\0";const char* fragmentShaderSource ="#version 330 core\n""out vec4 FragColor;\n""in vec3 color;\n""in vec2 uv;\n""uniform sampler2D sampler;\n""void main()\n""{\n""  FragColor = texture(sampler, uv);\n""}\n\0";//2 创建Shader程序（vs、fs）GLuint vertex, fragment;vertex = glCreateShader(GL_VERTEX_SHADER);fragment = glCreateShader(GL_FRAGMENT_SHADER);//3 为shader程序输入shader代码glShaderSource(vertex, 1, &vertexShaderSource, NULL);glShaderSource(fragment, 1, &fragmentShaderSource, NULL);int success = 0;char infoLog[1024];//4 执行shader代码编译 glCompileShader(vertex);//检查vertex编译结果glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);if (!success) {glGetShaderInfoLog(vertex, 1024, NULL, infoLog);std::cout << "Error: SHADER COMPILE ERROR --VERTEX" << "\n" << infoLog << std::endl;}glCompileShader(fragment);//检查fragment编译结果glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);if (!success) {glGetShaderInfoLog(fragment, 1024, NULL, infoLog);std::cout << "Error: SHADER COMPILE ERROR --FRAGMENT" << "\n" << infoLog << std::endl;}//5 创建一个Program壳子program = glCreateProgram();//6 将vs与fs编译好的结果放到program这个壳子里glAttachShader(program, vertex);glAttachShader(program, fragment);//7 执行program的链接操作，形成最终可执行shader程序glLinkProgram(program);//检查链接错误glGetProgramiv(program, GL_LINK_STATUS, &success);if (!success) {glGetProgramInfoLog(program, 1024, NULL, infoLog);std::cout << "Error: SHADER LINK ERROR " << "\n" << infoLog << std::endl;}//清理glDeleteShader(vertex);glDeleteShader(fragment);
}
GLuint genTexture(const char* picPath, int unitTexturt)
{//1 stbImage 读取图片int width, height, channels;//--反转y轴stbi_set_flip_vertically_on_load(true);unsigned char* data = stbi_load(picPath, &width, &height, &channels, STBI_rgb_alpha);//2 生成纹理并且激活单元绑定GLuint texture = 0;glGenTextures(1, &texture);//--激活纹理单元--glActiveTexture(GL_TEXTURE0 + unitTexturt);//--绑定纹理对象--glBindTexture(GL_TEXTURE_2D, texture);//3 传输纹理数据,开辟显存glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);//为当前纹理对象生成mipmapglGenerateMipmap(GL_TEXTURE_2D);//***释放数据stbi_image_free(data);//4 设置纹理的过滤方式glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);//*****重要*****////GL_NEAREST:在单个mipmap上采用最邻近采样//GL_LINEAR   //MIPMAP_LINEAR：在两层mipmap之间采用线性插值//MIPMAP_NEARESTglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);//5 设置纹理的包裹方式glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);//uglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);//vreturn texture;
}
void prepareTextrue()
{//GLuint grassTexture = genTexture("grass.jpg", 0);//GLuint landTexture = genTexture("land.jpg", 1);//GLuint noiseTexture = genTexture("noise.jpg", 2);GLuint wallTexture = genTexture("goku.jpg", 0);
}void render()
{//执行opengl画布清理操作glClear(GL_COLOR_BUFFER_BIT);//1.绑定当前的programglUseProgram(program);//2 更新Uniform的时候，一定要先UserProgram//2.1 通过名称拿到Uniform变量的位置Location//2.2 通过Location更新Uniform变量的值GLint time = glGetUniformLocation(program, "time");int i = glfwGetTime();glUniform1f(time, glfwGetTime());GLint sampler = glGetUniformLocation(program, "sampler");glUniform1i(sampler, 0);//3 绑定当前的vaoglBindVertexArray(vao);//4 发出绘制指令//glDrawArrays(GL_TRIANGLE_STRIP, 0, 6);glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);
}int main()
{//初始化glfw环境glfwInit();//设置opengl主版本号glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);//设置opengl次版本号glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);//设置opengl启用核心模式glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//创建窗体对象GLFWwindow* window = glfwCreateWindow(800, 600, "lenarnOpenGL", nullptr, nullptr);//设置当前窗体对象为opengl的绘制舞台glfwMakeContextCurrent(window);//窗体大小回调glfwSetFramebufferSizeCallback(window, frameBufferSizeCallbakc);//键盘相应回调glfwSetKeyCallback(window, glfwKeyCallback);//使用glad加载所有当前版本opengl的函数if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "初始化glad失败" << std::endl;return -1;};//设置opengl视口大小和清理颜色glViewport(0, 0, 800, 600);glClearColor(0.2f, 0.3f, 0.3f, 1.0f);//shaderprepareShader();//vaoprepareVAO();//textureprepareTextrue();//执行窗体循环while (!glfwWindowShouldClose(window)){//接受并分发窗体消息//检查消息队列是否有需要处理的鼠标、键盘等消息//如果有的话就将消息批量处理，清空队列glfwPollEvents();//渲染操作render();//切换双缓存glfwSwapBuffers(window);}//推出程序前做相关清理glfwTerminate();return 0;
}