OpenGL教程：6. UV坐标系和利用stb_image库导入纹理贴图

之前的教程都是单一颜色的形状，这并不好看哈。所以我们给他增加个贴图！

stb_image库

我们利用stb_image读取纹理，其仓库地址：https://github.com/nothings/stb

注意我们只需要一个stb_image.h来读取纹理，其他库暂时是用不到的：

UV坐标系

读取纹理需要用到UV坐标系。这个坐标系

//
// Created by inver on 2022/9/12.
//
#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include "Shader/Shader.h"

#include "stb/stb_image.h"

int main() {
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    GLFWwindow *window = glfwCreateWindow(800, 600, "纹理和材质", nullptr, nullptr);
    if (window == nullptr) {
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc) glfwGetProcAddress)) {
        glfwTerminate();
        return -1;
    }

    float vertices[] = {
            //  顶点坐标                       //颜色                        //纹理坐标，注意x方向坐标轴为s,y方向坐标轴为T
            0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f,
            0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f,
            -0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f,
            -0.5f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f
    };

    int indices[] = {
            0, 1, 3,
            1, 2, 3
    };

    unsigned int vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    unsigned int vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    unsigned int ebo;
    glGenBuffers(1, &ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    //  position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *) nullptr);
    glEnableVertexAttribArray(0);

    //  color attribute
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *) (3 * sizeof(float)));
    glEnableVertexAttribArray(1);

    //  texture coord attribute
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void *) (6 * sizeof(float)));
    glEnableVertexAttribArray(2);

    //  下面的步骤不可以更换，要按照先生成纹理，然后读取文件的步骤
    //  生成纹理、并绑定纹理0
    unsigned int texture;
    glGenTextures(1, &texture);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture);
    //  设置纹理对象的环绕方式、过滤方式
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    //  读取纹理图片
    int width, height, nrChannels;
    stbi_set_flip_vertically_on_load(true);
    unsigned char *data = stbi_load("texture/happy.jpeg", &width, &height, &nrChannels,
                                    0);
    if (data) {
        // --------JPEG需要设置对齐方式--------
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
      	// --------JPEG需要设置对齐方式--------
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    } else {
        std::cout << "Error: Failed to Load Texture! \n";
    }
    stbi_image_free(data);

    std::string vsh = "shaders/texture/texture.vsh";
    std::string fsh = "shaders/texture/texture.fsh";
    Shader shader(vsh, fsh);

    glUniform1i(glGetUniformLocation(shader.id, "ourTexture"), 0);

    while (!glfwWindowShouldClose(window)) {
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
      
    		shader.use();
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwTerminate();
}

顶点着色器

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;

out vec3 ourColor;
out vec2 TexCoord;

void main(){
    gl_Position = vec4(aPos, 1.0f);
    ourColor = aColor;
    TexCoord = aTexCoord;
}

片元着色器

#version 330 core
out vec4 FragColor;

in vec3 ourColor;
in vec2 TexCoord;

uniform sampler2D ourTexture;

void main(){
    FragColor = texture(ourTexture, TexCoord);    //参数一为纹理，参数二为纹理坐标
}