linux之设备屏幕截图

在TQ2440上运行程序的时候，有时候需要把屏幕进行截图，只需要把屏幕上的像素点都保存为一张位图即可。

流程是：

1、打开设备/dev/fb/0

2、读取设备，把数据读入缓冲区

3、添加bmp图片头信息，保存即可。

程序如下：

int main(int argc, char *argv[])
{
    int m_Width = 480;
    int m_Height = 272;
    unsigned char buf[m_Width*m_Height*2];
    char *filename = "./fbshot.bmp";
    int fb;
    fb = open("/dev/fb/0", O_RDONLY);
    if(fb < 0)
        exit(1);
    if(argc == 2)
        filename = argv[1];
    read(fb, buf, m_Width*m_Height*2);
    close(fb);
    printf("Printing screen...\n");
    SaveBMPFile(buf, filename);
    printf("Printing screen finish!\n");
    exit(0);
}

保存为BMP图像的程序如下：

static unsigned char sg_BHeader[] = {
    0x42, 0x4D, 0x36, 0x58, 0x02, 0x00, 0x00, 0x00,  0x00, 0x00, 0x36, 0x00, 0x00, 0x00, 0x28, 0x00, 
    0x00, 0x00, 0x40, 0x01, 0x00, 0x00, 0xF0, 0x00,  0x00, 0x00, 0x01, 0x00, 0x10, 0x00, 0x00, 0x00, 
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
#define RGB565TO1555(rgb) ((unsigned short)((unsigned short)(rgb & 0x001f) | ((unsigned short)(rgb & 0xffe0) >> 1)))

void SaveBMPFile(unsigned char *raw, char *filename)
{
    unsigned short *p = (unsigned short *)raw;
    typedef unsigned int UINT;
    typedef unsigned char UCHAR;
    UINT m_Width = 480, m_Height = 272;//根据设备的屏幕大小定义。
    UINT i, j;
    int bmp = open(filename, O_WRONLY | O_CREAT);
    if(bmp < 0)
        return;
    sg_BHeader[0x02] = (UCHAR)(m_Width * m_Height * 2 + 0x36) & 0xff;
    sg_BHeader[0x03] = (UCHAR)((m_Width * m_Height * 2 + 0x36) >> 8) & 0xff;
    sg_BHeader[0x04] = (UCHAR)((m_Width * m_Height * 2 + 0x36) >> 16) & 0xff;
    sg_BHeader[0x05] = (UCHAR)((m_Width * m_Height * 2 + 0x36) >> 24) & 0xff;
    sg_BHeader[0x12] = (UCHAR)m_Width & 0xff;
    sg_BHeader[0x13] = (UCHAR)(m_Width >> 8) & 0xff;
    sg_BHeader[0x14] = (UCHAR)(m_Width >> 16) & 0xff;
    sg_BHeader[0x15] = (UCHAR)(m_Width >> 24) & 0xff;
    sg_BHeader[0x16] = (UCHAR)(m_Height >> 8) & 0xff;
    sg_BHeader[0x17] = (UCHAR)(m_Height >> 16) & 0xff;
    sg_BHeader[0x18] = (UCHAR)(m_Height >> 24) & 0xff;
    write(bmp, sg_BHeader, sizeof(sg_BHeader));
    for(i = 0; i < m_Height; i++)
    {
        unsigned short *c = p + (m_Height - 1 - i) * m_Width;
        unsigned short cc;
        for(j = 0; j < m_Width; j++)
        {
            cc = RGB565TO1555(*(c + j));
            write(bmp, &cc, 2);
        }
    }
    close(bmp);
}