GLFW5 ——纹理应用

纹理是一种GL对象，创建方式与顶点数据类似

    int width_, height_;
    unsigned char* image = SOIL_load_image("container.jpg", &width_, &height_, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width_, height_, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);
    
    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);
    
    glBindTexture(GL_TEXTURE_2D, 0);

纹理显示到fragment前，还需要设置它的纹理坐标。
纹理坐标和顶点坐标有点不同，它指的是纹理的映射点。纹理像素（Texile）和屏幕像素不是一一对应的

    // Set up vertex data (and buffer(s)) and attribute pointers
    GLfloat vertices[] = {
        //     ---- 位置 ----       ---- 颜色 ----     - 纹理坐标 -
        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,   // 右下
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f,   // 左下
        -0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 1.0f,    // 左上
        0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,   1.0f, 1.0f,   // 右上
        -0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f,   // 左下
    };

    GLuint VBO, VAO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    // Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).
    glBindVertexArray(VAO);
    
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);
    
    glVertexAttribPointer(2, 2, GL_FLOAT,GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);
    
    glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind
    
    glBindVertexArray(0); // Unbind VAO (it's always a good thing to unbind any buffer/array to prevent strange bugs)

这段代码里，我们把顶点位置、颜色、纹理坐标储存在一个VAO中。
shader改变一下，颜色从纹理中采样

#version 330 core
in vec3 ourColor;
out vec4 color;
in vec2 TexCoord;

uniform sampler2D ourTexture;

void main()
{    color = texture(ourTexture, TexCoord);
}

texture函数传入纹理对象和纹理坐标，返回对应点点颜色值！

        glBindTexture(GL_TEXTURE_2D, texture);
                
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 6);
                
        glBindVertexArray(0);

当只有一个纹理时，不需要用glUniform像shader中传值！