OpenGL中的shader

主要是顶点着色器与片段着色器（这之间已经顶点着色器之前还有许多阶段，此处省略

顶点着色器为我们试图渲染的每个顶点调用，与实际图形无关，只是指定了你想要的位置的方式，也被用来解析数据从属性到下一阶段（在片段着色器

片段着色器为每个需要光栅化的像素运行一次，可以理解为涂色的像素格子，调用次数取决于需要绘制的像素数量

#include<GL/glew.h>
#include <GLFW/glfw3.h>

#include<iostream>

//创建着色器
static unsigned int CompileShader(unsigned int type, const std::string& source)
{
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE)
    {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed To Compile"<<(type == GL_VERTEX_SHADER ? "vertex" : "fragmenrt")<<" Shader Nya~" << std::endl;
        std::cout << message << std::endl;

        glDeleteShader(id);
        return 0;
    }
    return id;
}
static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader) 
{
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER,vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;
}
int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    glewInit();

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "OpenGl", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK) {
        std::cout << "Error" << std::endl;
    }
    std::cout << glGetString(GL_VERSION) << std::endl;

    float position[6] = {
        -0.5f, -0.5f,
         0.0f,  0.5f,
         0.5f, -0.5f
    };
    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER,sizeof(position),position,GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    //把着色器作为字符串传进去
    //这并不是好的方法（
    //下期解决
    std::string vertexShader = 
        "#version 330 core\n"
        "\n"
        "layout(location = 0) in vec4 position;\n"
        "\n"
        "void main()\n"
        "{\n"
        "   gl_Position = position;\n"
        "}\n";
    std::string fragmentShader =
        "#version 330 core\n"
        "\n"
        "layout(location = 0) out vec4 color;"
        "\n"
        "void main()\n"
        "{\n"
        "   color = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n";
    unsigned int shader = CreateShader(vertexShader,fragmentShader);
    glUseProgram(shader);

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES,0,3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}