如何在 OpenGL 3.3 中修复黑屏输出

Question

我在使用 OpenGL 和 C++ 的项目中遇到黑屏。我需要有关在屏幕上渲染红色三角形时出错的地方的帮助。

我已尝试检查顶点和片段着色器中的错误。

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

using namespace std;

unsigned int CreateShader(int type, const string shaderSource) {
    unsigned int shader = glCreateShader(type);
    const char *src = shaderSource.c_str();
    glShaderSource(shader, 1, &src, NULL);
    glCompileShader(shader);

    int result;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);
        char *message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(shader, length, &length, message);
        cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex shader " : "fragment shader ") << endl;
        cout << message << endl;
    }


    return shader;
}

unsigned int CreateProgram(const string vertexShader, const string fragmentShader) {
    unsigned int program = glCreateProgram();

    unsigned int vs = CreateShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CreateShader(GL_FRAGMENT_SHADER, fragmentShader);

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

    glDeleteShader(vs);
    glDeleteShader(fs);

    glLinkProgram(program);
    glValidateProgram(program);

    return program;

}

int main() {

    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    GLFWwindow *window = glfwCreateWindow(800, 600, "window", NULL, NULL);

    glfwMakeContextCurrent(window);

    glewInit();
    if (glewInit() != GLEW_OK) {
        cout << "Glew initialization Failed! " << endl;
        glfwTerminate();
        return -1;
    }

    float positions[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f, 0.5f, 0.0f,
    };

    cout << "Made By Rial Seebran" << endl;
    cout << glfwGetVersionString() << endl;


    unsigned int VAO;
    unsigned int VBO;

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    const string vertexShader =
        "#version 330 core\n"
        "layout (location = 0) in vec3 position;\n"
        "void main() {\n"
        "gl_Position = vec4(position, 0.0f);\n"
        "}\n";

    const string fragmentShader =
        "#version 330 core\n"
        "layout (location = 0) out vec4 color;\n"
        "void main() {\n"
        "color = vec4(1.0f, 0.0f, 0.0f, 1.0f);\n"
        "}\n";

    unsigned int program = CreateProgram(vertexShader, fragmentShader);


    while (!glfwWindowShouldClose(window)) {
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(program);
        glBindVertexArray(VAO);
        glDrawArrays(GL_ARRAY_BUFFER, 0, 3);
        glBindVertexArray(0);

        glfwPollEvents();
        glfwSwapBuffers(window);
    }
    glfwTerminate();
    return 0;
}

我希望在指定的坐标处绘制一个带有蓝色背景的红色三角形。

Answer 1

glDrawArrays 的第一个参数必须是原始类型。
它必须是GL_TRIANGLES 而不是GL_ARRAY_BUFFER：

glDrawArrays(GL_ARRAY_BUFFER, 0, 3);
glDrawArrays(GL_TRIANGLES, 0, 3);

OpenGL 枚举器常量GL_ARRAY_BUFFER 不是该参数可接受的值，将导致GL_INVALID_ENUM 错误（该错误可以通过glGetError 得到）。

---

当剪辑空间坐标转换为规范化设备空间时，x、y 和 z 分量除以w 分量。 这意味着gl_Position 的w 组件必须设置为1.0 而不是0.0：

gl_Position = vec4(position, 0.0f);
gl_Position = vec4(position, 1.0);

---

Glew 可以通过glewExperimental = GL_TRUE; 启用其他扩展。请参阅GLEW documentation，它说：

GLEW 从图形驱动程序获取有关支持的扩展的信息。然而，实验性或预发布驱动程序可能不会通过标准机制报告每个可用的扩展，在这种情况下，GLEW 将报告它不受支持。为了避免这种情况，可以在调用glewInit()之前将glewExperimental全局开关设置为GL_TRUE，这样可以确保所有具有有效入口点的扩展都会被暴露。

glewExperimental = GL_TRUE;
if ( glewInit() != GLEW_OK ) {
    cout << "Glew initialization Failed! " << endl;
    glfwTerminate();
    return -1;
}