在linux系統中,使用framebuffer來提供使用者態程序直接操作顯示屏的功能.

在嵌入式系統開發中,需要對顯示屏的內容進行擷取,實現一個lcd截圖工具實現對顯示屏內容的擷取,儲存為bmp格式.

一個bmp檔案有四部分組成:

其中點陣圖檔案頭內容如下:

    WORD    bfType; 
    DWORD   bfSize; 
    WORD    bfReserved1; 
    WORD    bfReserved2; 
    DWORD   bfOffBits; 

    DWORD  biSize; 
    LONG   biWidth; 
    LONG   biHeight; 
    WORD   biPlanes; 
    WORD   biBitCount 
    DWORD  biCompression; 
    DWORD  biSizeImage; 
    LONG   biXPelsPerMeter; 
    LONG   biYPelsPerMeter; 
    DWORD  biClrUsed; 
    DWORD  biClrImportant; 
 

實現程式碼如下:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/soundcard.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>

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 & 0xffc0) >> 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 = 800, m_Height = 480;
    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 & 0xff;
    sg_BHeader[0x17] = (UCHAR)(m_Height >> 8) & 0xff;
    sg_BHeader[0x18] = (UCHAR)(m_Height >> 16) & 0xff;
    sg_BHeader[0x19] = (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));
//            cc = *(c + j);
            write(bmp, &cc, 2);
        }
    }
    close(bmp);
}
int main(int argc, char *argv[])
{
    unsigned char buf[800*480*2];
    char *filename;
    int fb;

    
    fb = open("/dev/fb0", O_RDONLY);
    if(fb < 0)
        exit(1);
    if(argc == 2)
        filename = argv[1];
    else
        exit(1);
    printf("reading screen...\n");
    read(fb, buf, 800*480*2);
    close(fb);
    printf("saving screen...\n");
    SaveBMPFile(buf, filename);
    printf("file %s created successfully\n", filename);
    exit(0);
}