白屏（OpenGL）

Question

我是 OpenGL 新手，我想用我的着色器在屏幕上绘制一个简单的三角形。我设置了缓冲区并编写了一个着色器，但它似乎不起作用。它给出了白屏，我试图用 glGenBuffer 更改 glCreateBuffer 并将屏幕变成黑屏。我想在一个名为 createAndCompileShader(...) 的函数中创建和编译着色器，缓冲区在主函数中定义。

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

static unsigned int createAndCompileShader(const char* vertexShader, const char* fragmentShader) {

    unsigned int fragmentShaderr = glCreateShader(GL_FRAGMENT_SHADER);
    unsigned int vertexShaderr = glCreateShader(GL_VERTEX_SHADER);

    glShaderSource(vertexShaderr, 1, &vertexShader, NULL);
    glShaderSource(fragmentShaderr, 1, &fragmentShader, NULL);

    glCompileShader(vertexShaderr);
    glCompileShader(fragmentShaderr);

    unsigned int program = glCreateProgram();

    glAttachShader(program, vertexShaderr);
    glAttachShader(program, fragmentShaderr);
    glLinkProgram(program);
    

    return program;
}


int main(void)
{
    GLFWwindow* window;

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

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

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

    float vertexPositions[6] = {
             -0.5, -0.5,
             0.0, 0.5,
             0.5, -0.5
    };


    const char* vertexShader = "#version 330 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main()\n"
        "{\n"
        "gl_Position = position;\n"
        "}\n";

    const char* fragementShader = "#version 330 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main()\n"
        "{\n"
        "color = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n";

    unsigned int program = createAndCompileShader(vertexShader, fragementShader);

    glUseProgram(program);

    unsigned int buffer;

    glGenBuffers(1, &buffer);
    //glCreateBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertexPositions, GL_STATIC_DRAW);

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

  
    //std::string vertexShader;
    //std::string fragmentShader;

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


        glDrawArrays(GL_TRIANGLES, 0 ,3);

        /*glBegin(GL_TRIANGLES);
        glVertex2f(-0.5, -0.5);
        glVertex2f( 0.0, 0.5);
        glVertex2f( 0.5, -0.5);
        glEnd();*/

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

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

    glDeleteProgram(program);

    glfwTerminate();
    return 0;
}

Answer 1

GLSL 3.30 中未提供片段着色器输入布局位置限定符。您必须切换到 GLSL 4.10 或删除片段着色器中的布局位置：

layout(location = 0) in vec4 position;

in vec4 position;

此外，您还错过了片段着色器输出 color 的规范。

#version 330 core
in vec4 position;
out vec4 color;
void main()
{
    color = vec4(1.0, 0.0, 0.0, 1.0);
}

我推荐使用Raw string liters:

const char* fragementShader = R"(#version 330 core
in vec4 position;
out vec4 color;
void main()
{
    color = vec4(1.0, 0.0, 0.0, 1.0);
})";

检查着色器编译是否成功，程序对象是否链接成功。
如果着色器编译成功可以通过glGetShaderiv和参数GL_COMPILE_STATUS来检查。
程序链接是否成功可以通过glGetProgramiv和参数GL_LINK_STATUS来检查。
（查看this问题的答案。）

---

如果您使用核心配置文件 OpenGL 上下文，则默认的 Vertex Array Object 无效。创建一个命名的 VAO：

unsigned int VAO;
glCreateVertexArrays(1, &VAO);
glBindVertexArray(VAO);

unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertexPositions, GL_STATIC_DRAW);

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

---

GLEW 必须由 glewInit() 初始化。见Initializing GLEW：

glfwMakeContextCurrent(window);
glewInit();