c++ - 基础 openGL |黑屏

Question

这个程序应该渲染一个三角形，但只显示黑屏。

我已更新此代码以反射(reflect)答案/评论中建议的更改。

[Ubuntu 16.04、GLFW、GLEW]

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

#include <stdio.h>

int main(int argc, char* argv[])
{

    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 Practice", NULL,     NULL);
    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;
    glewInit();

    GLfloat verts[] = {
        +0.0f, +1.0f,
        -1.0f, -1.0f,
        +1.0f, -1.0f
    };

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

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts, GL_STATIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);

    // glVertexPointer(2, GL_FLOAT, 0, 0);

    // Main loop
    while (!glfwWindowShouldClose(window))
    {
        glfwPollEvents();

        if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        {
            glfwSetWindowShouldClose(window, GL_TRUE);
        }

        glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);


    }

    glfwTerminate();

    return 0;
}

[更新:似乎此代码所基于的教程使用的是更旧版本的 openGL，其中不需要着色器。对于初学者来说，这非常难以找到，因为设置完全相同并且没有编译或运行时错误。我在下面将最接近此解释的答案标记为正确。]

Answer 1

即使您创建了 VBO 和 VAO 并填充了它们，您也没有正确使用它们。

您首先需要绑定(bind) VAO，然后绑定(bind) VBO，然后将数据复制到缓冲区并使用 glVertexAttribPointer() 函数，然后取消绑定(bind)两个缓冲区。

然后在渲染前再次绑定(bind)VAO，绘制完成后解绑。

您还需要 SHADERS

我在您的代码中没有看到任何着色器。

这是一个工作代码:

#include <iostream>

// GLEW
#define GLEW_STATIC
#include <GL/glew.h>

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


// Function prototypes
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);

// Window dimensions
const GLuint WIDTH = 800, HEIGHT = 600;

// Shaders
const GLchar* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 position;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(position.x, position.y, position.z, 1.0);\n"
"}\0";
const GLchar* fragmentShaderSource = "#version 330 core\n"
"out vec4 color;\n"
"void main()\n"
"{\n"
"color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\n\0";

// The MAIN function, from here we start the application and run the game loop
int main()
{
// Init GLFW
glfwInit();
// Set all the required options for GLFW
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

// Create a GLFWwindow object that we can use for GLFW's functions
GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);
glfwMakeContextCurrent(window);

// Set the required callback functions
glfwSetKeyCallback(window, key_callback);

// Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions
glewExperimental = GL_TRUE;
// Initialize GLEW to setup the OpenGL Function pointers
glewInit();

// Define the viewport dimensions
int width, height;
glfwGetFramebufferSize(window, &width, &height);  
glViewport(0, 0, width, height);


// Build and compile our shader program
// Vertex shader
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// Check for compile time errors
GLint success;
GLchar infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
    glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
    std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// Fragment shader
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// Check for compile time errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
    glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
    std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// Link shaders
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// Check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
    glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
    std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);


// Set up vertex data (and buffer(s)) and attribute pointers
GLfloat vertices[] = {
    -0.5f, -0.5f, 0.0f, // Left  
     0.5f, -0.5f, 0.0f, // Right 
     0.0f,  0.5f, 0.0f  // Top   
};
GLuint VBO, VAO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
// Bind the Vertex Array Object first, then bind and set vertex buffer(s) and attribute pointer(s).
glBindVertexArray(VAO);

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

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind

glBindVertexArray(0); // Unbind VAO (it's always a good thing to unbind any buffer/array to prevent strange bugs)

// Game loop
while (!glfwWindowShouldClose(window))
{
    // Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions
    glfwPollEvents();

    // Render
    // Clear the colorbuffer
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    // Draw our first triangle
    glUseProgram(shaderProgram);
    glBindVertexArray(VAO);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glBindVertexArray(0);

    // Swap the screen buffers
    glfwSwapBuffers(window);
}
// Properly de-allocate all resources once they've outlived their purpose
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
// Terminate GLFW, clearing any resources allocated by GLFW.
glfwTerminate();
return 0;
}

// Is called whenever a key is pressed/released via GLFW
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
    glfwSetWindowShouldClose(window, GL_TRUE);
}

来源:https://learnopengl.com/code_viewer.php?code=getting-started/hellotriangle

我建议您从头开始学习 OpenGL。 https://learnopengl.com/是学习 OpenGL 的好地方。