(十二)纹理和采样

纹理

在绘制三角形的过程中，将图片贴到三角形上进行显示的过程，就是纹理贴图的过程

uv坐标

如果如果图片尺寸和实际贴图尺寸不一致，就会导致像素不够用了的问题

纹理与采样

纹理对象(Texture)：在GPU端，用来以一定格式存放纹理图片描述信息和数据信息的对象
采样器(Sampler)：在GPU端，用来根据uv坐标以一定算法从纹理内容中获取颜色的过程称为采样，执行采样的对象为采样器

使用stbImage库(只需要头文件)读取图片

stbi_uc *stbi_load(char const *filename, int *x, int *y, int *comp, int req_comp)

filename：图片路径
x,y：图片宽度和高度
comp：读取图片本身的通道种类(RGP/RGBA/GREY)
req_comp：期望读出来的通道种类(RGP/RGBA/GREY)

读取出来的图片以左上方为原点，而opengl是左下方为原点，因此读取出来的图片必须反转y轴

stbi_set_flip_vertically_on_load(true);

上述代码即可将转换为opengl坐标

纹理单元

用于链接采样器(Sampler)和纹理对象(Texture)，让Sampler知道去哪个纹理对象采样

创建纹理对象

纹理过滤

纹理包裹

当uv坐标超出了0-1范围，该怎么办

• Repeat：重复纹理
• Mirrored：镜像纹理
• ClampToEdge：边缘复用
• ClampToBorder：设置边缘颜色，且复用
  
  
  
  
  

#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;
GLuint texture = 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""void main()\n""{\n""   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 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);
}void prepareTextrue()
{//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("goku.jpg", &width, &height, &channels, STBI_rgb_alpha);//2 生成纹理并且激活单元绑定glGenTextures(1, &texture);//--激活纹理单元--glActiveTexture(GL_TEXTURE0);//--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);//***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);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);//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);//v
}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LocationGLint location = glGetUniformLocation(program, "sampler");//2.2 通过Location更新Uniform变量的值glUniform1f(location, 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;
}

上面这个例子中，成功的将一张图片绘制到了三角形中。
在vao中加入uv坐标描述信息，vs中读取vao中的uv信息传递给fs，fs中加入采样器uniform变量，在渲染时设置采样器的值和采样单元值一致即可。