用glReadPixels保存显示的界面

#include <GL/glut.h>
#include <iostream>
#include <fstream>
#include <vector>

// Save pixel data as BMP image
void saveBMP(const std::string& filename, int width, int height, const std::vector<GLubyte>& data) {
    std::ofstream file(filename, std::ios::binary);

    if (!file) {
        std::cerr << "Error opening file for writing" << std::endl;
        return;
    }

    int imageSize = width * height * 3; // RGB data, 3 bytes per pixel
    int fileSize = 54 + imageSize; // BMP header size + image size

    unsigned char bmpFileHeader[14] = {
        'B', 'M', // Magic number
        static_cast<unsigned char>(fileSize), static_cast<unsigned char>(fileSize >> 8),
        static_cast<unsigned char>(fileSize >> 16), static_cast<unsigned char>(fileSize >> 24),
        0, 0, 0, 0, // Reserved
        54, 0, 0, 0 // Offset to pixel data
    };

    unsigned char bmpInfoHeader[40] = {
        40, 0, 0, 0, // Info header size
        static_cast<unsigned char>(width), static_cast<unsigned char>(width >> 8),
        static_cast<unsigned char>(width >> 16), static_cast<unsigned char>(width >> 24),
        static_cast<unsigned char>(height), static_cast<unsigned char>(height >> 8),
        static_cast<unsigned char>(height >> 16), static_cast<unsigned char>(height >> 24),
        1, 0, // Number of color planes
        24, 0, // Bits per pixel (RGB)
        0, 0, 0, 0, // Compression method
        0, 0, 0, 0, // Image size
        0, 0, 0, 0, // Horizontal resolution
        0, 0, 0, 0, // Vertical resolution
        0, 0, 0, 0, // Number of colors in color palette
        0, 0, 0, 0 // Number of important colors
    };

    file.write(reinterpret_cast<char*>(bmpFileHeader), sizeof(bmpFileHeader));
    file.write(reinterpret_cast<char*>(bmpInfoHeader), sizeof(bmpInfoHeader));
    file.write(reinterpret_cast<const char*>(&data[0]), imageSize);

    file.close();
}

void display() {
    // Your OpenGL drawing code here
    // ...
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // Clear color to black
    glClear(GL_COLOR_BUFFER_BIT); // Clear the color buffer

    // Draw something on the screen
    glBegin(GL_TRIANGLES);
    glColor3f(1.0f, 0.0f, 0.0f); // Red color
    glVertex2f(-0.5f, -0.5f);
    glVertex2f(0.5f, -0.5f);
    glVertex2f(0.0f, 0.5f);
    glEnd();

    glFlush(); // Ensure all drawing commands are executed

    GLint viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport); // Get viewport dimensions

    int width = viewport[2];
    int height = viewport[3];

    std::vector<GLubyte> pixelData(width * height * 3); // RGB data

    if (!pixelData.empty()) {
        glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, &pixelData[0]);

        // Convert RGBA to BGR format for BMP
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                int index = (y * width + x) * 3;
                GLubyte temp = pixelData[index]; // Store red component
                pixelData[index] = pixelData[index + 2]; // Replace red with blue
                pixelData[index + 2] = temp; // Set blue to stored red
            }
        }

        saveBMP("screenshot.bmp", width, height, pixelData);
    }
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(800, 600);
    glutCreateWindow("OpenGL Screenshot Example");

    glutDisplayFunc(display);

    glutMainLoop();
    return 0;
}