无法使用OpenGL创建彩色三角形

Question

I'm following open.gl and I have gotten to the rendering stage but my triangle does not appear on the screen. Only a black box.

I'm on Win7, latest drivers and everything, VS2013.

To make it easy I put the code here:

#define GLEW_STATIC

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

using namespace std;


int main() {
    glfwInit();

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);

    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

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

    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;
    glewInit();

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

    GLuint vbo;
    glGenBuffers(1, &vbo);

    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    const char* vertexShaderCode =
        "#version 150\n"
        "in vec2 position;"
        "void main() {"
        "   gl_Position = vec4(position, 0.0, 1.0);"
        "}";

    const char* fragmentShaderCode =
        "#version 150\n"
        "out vec4 outColor;"
        "void main() {"
        "   outColor = vec4(1.0, 1.0, 1.0, 1.0);"
        "}";

    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexShaderCode, NULL);
    glCompileShader(vertexShader);

    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentShaderCode, NULL);
    glCompileShader(fragmentShader);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);

    glBindFragDataLocation(shaderProgram, 0, "outColor");

    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");

    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 0, 0);

    glEnableVertexAttribArray(posAttrib);

    GLuint vao;
    glGenVertexArrays(1, &vao);

    glBindVertexArray(vao);

    while(!glfwWindowShouldClose(window)) {  
        glfwPollEvents();
        glfwSwapBuffers(window);

        glDrawArrays(GL_TRIANGLES, 0, 3);
    }

    glfwTerminate();
}

Answer 1

Bind the VAO before you specify the vertex layout:

GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);

Answer 2

Check all glFw commands for failure. For debugging check glGetError after every OpenGL command. Also make sure your shaders have compiled correctly, if not make sure you print the error messages.

Lastly, check the viewport.