嵌入式linux通用截图工具

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文章出处：http://www.limodev.cn/blog
作者联系方式：李先静 <xianjimli at hotmail dot com>

为了截几张图片给broncho的A1做宣传，昨天写了一个截图工具。这个工具与其它截图工具不同的是，它不基于任何具体的GUI，直接从framebuffer中截图，然后保存为jpeg图片，所以适用于任何嵌入式linux设备。

o 打开framebuffer

static int fb_open(struct FB *fb, const char* fbfilename)
{
    fb->fd = open(fbfilename, O_RDWR);
    if (fb->fd < 0)
    {
        fprintf(stderr, "can't open %s/n", fbfilename);
        return -1;
    }
 
    if (ioctl(fb->fd, FBIOGET_FSCREENINFO, &fb->fi) < 0)
        goto fail;
    if (ioctl(fb->fd, FBIOGET_VSCREENINFO, &fb->vi) < 0)
        goto fail;
 
    fb->bits = mmap(0, fb_size(fb), PROT_READ | PROT_WRITE,
                    MAP_SHARED, fb->fd, 0);
    if (fb->bits == MAP_FAILED)
        goto fail;
 
    return 0;
fail:
    printf("%s is not a framebuffer./n", fbfilename);
    close(fb->fd);
 
    return -1;
}

o 读取数据并写入jpeg

static int snap(const char * filename, int quality, struct FB* fb)
{
    int row_stride = 0;
    FILE * outfile = NULL;
    JSAMPROW row_pointer[1] = {0};
    struct jpeg_error_mgr jerr = {0};
    struct jpeg_compress_struct cinfo = {0};
 
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);
 
    if ((outfile = fopen(filename, "wb+")) == NULL)
    {
        fprintf(stderr, "can't open %s/n", filename);
 
        return -1;
    }
 
    jpeg_stdio_dest(&cinfo, outfile);
    cinfo.image_width = fb_width(fb);
    cinfo.image_height = fb_height(fb);
    cinfo.input_components = 3;
    cinfo.in_color_space = JCS_RGB;
    jpeg_set_defaults(&cinfo);
    jpeg_set_quality(&cinfo, quality, TRUE);
    jpeg_start_compress(&cinfo, TRUE);
 
    row_stride = fb_width(fb) * 2;
    JSAMPLE* image_buffer = malloc(3 * fb_width(fb));
 
    while (cinfo.next_scanline < cinfo.image_height)
    {
        int i = 0;
        unsigned short* line = fb->bits + cinfo.next_scanline * fb_width(fb);
        for(i = 0; i < fb_width(fb); i++)
        {
            int offset = i * 3;
            unsigned short color = line[i];
            unsigned char r = ((color >> 11) & 0xff) << 3;
            unsigned char g = ((color >> 5) & 0xff)  << 2;
            unsigned char b = (color & 0xff )<< 3;
            image_buffer[offset]     = r;
            image_buffer[offset + 1] = g;
            image_buffer[offset + 2] = b;
        }
 
        row_pointer[0] = image_buffer;
        (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
 
    jpeg_finish_compress(&cinfo);
    fclose(outfile);
 
    jpeg_destroy_compress(&cinfo);
 
    return 0;
}

o 主函数

int main(int argc, char* argv[])
{
    struct FB fb = {0};
    const char* filename   = NULL;
    const char* fbfilename = NULL;
 
    if(argc != 3)
    {   
        printf("/nusage: %s [jpeg] [framebuffer]/n", argv[0]);
        printf("-----------------------------------------/n");
        printf("Powered by broncho(www.broncho.cn)/n");
        return 0;
    }
 
    filename   = argv[1];
    fbfilename = argv[2];
    if (fb_open(&fb, fbfilename) == 0)
    {
        snap(filename, 100, &fb);
        fb_close(&fb);
    }
 
    return 0;
}

完整代码请到这里 下载。