现代OpenGL（一）：我的第一个OpenGL程序

#include <GL/glew.h>
#include <SFML/Window.hpp>

#define GLSL(src) "#version 150 core\n" #src

// Vertex渲染器代码片段
const GLchar* vertexSource = GLSL(
    in vec2 position;
    in vec3 color;
    out vec3 mColor;
    void main() {
        mColor = color;
        gl_Position = vec4(position, 0.0f, 1.0f);
    }
);

// Fragment渲染器片段
const GLchar* fragmentSource = GLSL(
    in vec3 mColor;
    out vec4 oColor;
    void main() {
        oColor = vec4(mColor, 1.0f);
    }
);

// 创建指定类型的Shader
GLuint createShader(GLenum type, const GLchar* src)
{
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &src, nullptr);
    glCompileShader(shader);
    return shader;
}

int main(int argc, char* argv[])
{
    // 初始化Window窗口
    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;

    const unsigned int WIDTH = 800;
    const unsigned int HEIGHT = 600;
    const sf::String TITLE = "Modern OpenGL";
    sf::Window window(sf::VideoMode(WIDTH, HEIGHT, 32), TITLE, 
        sf::Style::Titlebar | sf::Style::Close, settings);

    // 初始化GLEW
    glewExperimental = GL_TRUE;
    glewInit();

    // 顶点数据
    GLfloat vertices[] = {
        0.0f, 0.5f, 1.0f, 0.0f, 0.0f,
        0.5f, -0.5f, 0.0f, 1.0f, 0.0f,
        -0.5f, -0.5f, 0.0f, 0.0f, 1.0f
    };

    // 创建Vertex Array Object
    GLuint VAO;
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    // 创建Vertex Buffer Object并装载数据
    GLuint VBO;
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // 创建Vertex渲染器和Fragment渲染器
    GLuint vertexShader = createShader(GL_VERTEX_SHADER, vertexSource);
    GLuint fragmentShader = createShader(GL_FRAGMENT_SHADER, fragmentSource);

    // 将Vertex渲染器和Fragment渲染器关联到Shader Program
    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    // 设置Vertex数据的布局属性（这里包括postion和color两个属性）
    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), 0);

    GLint colorAttrib = glGetAttribLocation(shaderProgram, "color");
    glEnableVertexAttribArray(colorAttrib);
    glVertexAttribPointer(colorAttrib, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)(2 * sizeof(GLfloat)));

    // 这个While循环是SFML的固定模式用于做事件处理
    while (window.isOpen())
    {
        // 内层While循环用于处理事件响应
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
                window.close();
        }
        window.setActive();
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        // 绘制图形
        glDrawArrays(GL_TRIANGLES, 0, 3);
        window.display();
    }
    // 释放资源
    glDeleteProgram(shaderProgram);
    glDeleteShader(fragmentShader);
    glDeleteShader(vertexShader);

    glDeleteBuffers(1, &VBO);
    glDeleteVertexArrays(1, &VAO);

    return EXIT_SUCCESS;
}

A Vertex Shader in OpenGL is a piece of C like code written to the GLSL specification which influences the attributes of a vertex. Vertex shaders can be used to modify properties of the vertex such as position, color, and texture coordinates.

A Fragment Shader is similar to a Vertex Shader, but is used for calculating individual fragment colors. This is where lighting and bump-mapping effects are performed.

A Vertex Array Object (VAO) is an object which contains one or more Vertex Buffer Objects and is designed to store the information for a complete rendered object. In our example this is a diamond consisting of four vertices as well as a color for each vertex.

A Vertex Buffer Object (VBO) is a memory buffer in the high speed memory of your video card designed to hold information about vertices. In our example we have two VBOs, one that describes the coordinates of our vertices and another that describes the color associated with each vertex. VBOs can also store information such as normals, texcoords, indicies, etc.