Linux下C语言实现LCD屏幕截图

一、概述

        最近看到网上有人问怎么用C语言实现屏幕截图，刚好自己也在研究Linux驱动，于是花了半天时间把Linux的FrameBuffer驱动看懂了个七八，接着就动手写了个LCD屏幕截图的应用程序。

     一些说明：

     1. 板子LCD的分辨率为480x272，像素格式为RGB565。

     2. 程序首先获取LCD的一些参数 ，然后将获取到的一帧数据转换为RGB24格式，最后用jpeglib库压缩为jpg格式的图片。

　  3. 在嵌入式Linux的板子上测试通过。

 

二、实现

       程序中有注释，不多说，直接上程序：

#include<stdio.h>
 #include<stdlib.h>
 #include<sys/ioctl.h>
 #include<unistd.h>
 #include<fcntl.h>
 #include <malloc.h>

 #include<linux/fb.h>

 #include <jpeglib.h>
 #include <jerror.h>


 /*RGB565转RGB24函数
 *@rgb565: 指向存放rgb565数据的起始地址
 *@rgb24：指向存放rgb24数据的起始地址
 *@width：屏幕（分辨率）的宽度
 *@height：屏幕（分辨率）的高度
 */
 int RGB565_to_RGB24(unsigned char *rgb565,unsigned char *rgb24,int width,int height)
 {
     int i;
     int whole = width*height;
     unsigned char r,g,b;
     unsigned short int *pix565;

     pix565 = (unsigned short int *)rgb565;

     for(i = 0;i < whole;i++)
     {
         r = ((*pix565)>>11)&0x1f;
         *rgb24 = (r<<3) | (r>>2);
         rgb24++;
         g = ((*pix565)>>5)&0x3f;
         *rgb24 = (g<<2) | (g>>4);
         rgb24++;
         b = (*pix565)&0x1f;
         *rgb24 = (b<<3) | (b>>2);
         rgb24++;
         pix565++;

     }
     return 1;
 }

 /*jpeg压缩函数
 *@rgb：指向存放rgb24数据的起始地址
 *@width：屏幕（分辨率）的宽度
 *@height：屏幕（分辨率）的高度
 */
 int jpeg_compress(unsigned char *rgb,int width,int height)
 {
         struct jpeg_compress_struct cinfo;
         struct jpeg_error_mgr jerr;
         FILE * outfile;
         JSAMPROW row_pointer[1];
         int row_stride;
         cinfo.err = jpeg_std_error(&jerr);
         jpeg_create_compress(&cinfo);
         //输出文件名为：out.jpg
         if ((outfile = fopen("out.jpg", "wb")) == NULL)
         {
             printf("can not open out.jpg\n");
             return -1;
         }
         jpeg_stdio_dest(&cinfo, outfile);

         cinfo.image_width = width;
         cinfo.image_height = height;
         cinfo.input_components = 3;
         //输入数据格式为RGB
         cinfo.in_color_space = JCS_RGB;

         jpeg_set_defaults(&cinfo);
         //压缩质量为80
         jpeg_set_quality(&cinfo, 80, TRUE );
         jpeg_start_compress(&cinfo, TRUE);
         row_stride = width * 3;

         while (cinfo.next_scanline < cinfo.image_height)
         {
             row_pointer[0] = &rgb[cinfo.next_scanline * row_stride];
             (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
         }

         jpeg_finish_compress(&cinfo);
         fclose(outfile);

         jpeg_destroy_compress(&cinfo);

         return 1;
 }


 int main()
 {

     int fd;
     struct fb_var_screeninfo fb_var_info;
     struct fb_fix_screeninfo fb_fix_info;
     unsigned char *trgb;
     unsigned char *rgb;
     int buffer_size;

     //打开framebuffer设备
     fd = open("/dev/fb0",O_RDONLY);
     if(fd < 0)
     {
         printf("can not open dev\n");
         exit(1);
     }

     //获取LCD的可变参数
     ioctl(fd,FBIOGET_VSCREENINFO,&fb_var_info);
     //一个像素多少位
     printf("bits_per_pixel: %d\n",fb_var_info.bits_per_pixel);
     //x分辨率
     printf("xres: %d\n",fb_var_info.xres);
     //y分辨率
     printf("yres: %d\n",fb_var_info.yres);
     //r分量长度（bit）
     printf("red_length: %d\n",fb_var_info.red.length);
     //g分量长度（bit）
     printf("green_length: %d\n",fb_var_info.green.length);
     //b分量长度（bit）
     printf("blue_length: %d\n",fb_var_info.blue.length);
     //t(透明度)分量长度（bit）
     printf("transp_length: %d\n",fb_var_info.transp.length);
     //r分量偏移
     printf("red_offset: %d\n",fb_var_info.red.offset);
     //g分量偏移
     printf("green_offset: %d\n",fb_var_info.green.offset);
     //b分量偏移
     printf("blue_offset: %d\n",fb_var_info.blue.offset);
     //t分量偏移
     printf("transp_offset: %d\n",fb_var_info.transp.offset);

     //获取LCD的固定参数
     ioctl(fd,FBIOGET_FSCREENINFO,&fb_fix_info);
     //一帧大小
     printf("smem_len: %d\n",fb_fix_info.smem_len);
     //一行大小
     printf("line_length: %d\n",fb_fix_info.line_length);

     //一帧大小
     buffer_size = (fb_var_info.xres * fb_var_info.yres * fb_var_info.bits_per_pixel/8);

     trgb = (unsigned char *)malloc(buffer_size);
     if(trgb==NULL)
         exit(0);
     rgb = (unsigned char *)malloc(fb_var_info.xres * fb_var_info.yres * 3);
     if(rgb==NULL)
     {
         goto here;
     }
     //获取一帧数据
     if(read(fd,trgb,buffer_size) < 0)
     {
         printf("reaf failed!\n");
         goto read_fail;
     }
     //格式转换
     RGB565_to_RGB24(trgb,rgb,fb_var_info.xres,fb_var_info.yres);
     //jpeg压缩
     if(jpeg_compress(rgb,fb_var_info.xres,fb_var_info.yres)<0)
         printf("compress failed!\n");

 read_fail:
     free(rgb);
 here:
     free(trgb);


     close(fd);

     return 0;
 }