開發板上顯示圖片

參考網址：  http://blog.csdn.net/z1179675084/article/details/14645359
                  http://hi.baidu.com/guoggn/item/636e08145b5d39fc746a8461
                  http://blog.chinaunix.net/uid-26669729-id-3077015.html
                  http://blog.csdn.net/luxiaoxun/article/details/7622988

關鍵：

1）字節對齊問題__attribute__((packed))   最大字節對齊

2） _attribute__((packed))的作用是告訴編譯器取消結構在編譯過程中的優化對齊  

3） 字節數的統計

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>  
#include <unistd.h>
#include <sys/mman.h> /*map頭文件*/
#include <linux/fb.h>     
#include <fcntl.h> 
#include <string.h>  
#include <arpa/inet.h>

 //14byte文件頭  
typedef struct  
{  
     unsigned char  cfType[2];//文件類型，"BM"(0x4D42)  
     unsigned int  cfSize;//文件大小（字節）  
     unsigned int cfReserved;//保留，值爲0  
     unsigned int  cfoffBits;//數據區相對於文件頭的偏移量（字節）  
}__attribute__((packed)) BITMAPFILEHEADER;  
/*_attribute__((packed))的作用是告訴編譯器取消結構在
編譯過程中的優化對齊  */

//40byte信息頭  
typedef struct  
{  
     unsigned int  ciSize;//BITMAPFILEHEADER所佔的字節數  
     unsigned int ciWidth;//寬度  
     unsigned int ciHeight;//高度  
     unsigned short int ciPlanes;//目標設備的位平面數，值爲1  
     unsigned short int  ciBitCount;//每個像素的位數  
     char ciCompress[4];//壓縮說明  
     unsigned int ciSizeImage;//用字節表示的圖像大小，該數據必須是4的倍數  
     unsigned int ciXPelsPerMeter;//目標設備的水平像素數/米  
     unsigned int ciYPelsPerMeter;//目標設備的垂直像素數/米  
     unsigned int ciClrUsed; //位圖使用調色板的顏色數  
     unsigned intciClrImportant; //指定重要的顏色數，當該域的值等於顏色數時（或者等於0時），表示所有顏色都一樣重要  
}__attribute__((packed)) BITMAPINFOHEADER;  
  
typedef struct  
{  
    unsigned char  blue;  
    unsigned char green;  
    unsigned char red;  
}__attribute__((packed)) PIXEL;//顏色模式RGB  
  
BITMAPFILEHEADER FileHead;  
BITMAPINFOHEADER InfoHead;  
static int xres = 0;  
static int yres = 0;  
static int bits_per_pixel = 0;  
static char *fb_addr = NULL;  

int show_bmp(char *picname)  
{
    FILE *fp;  
    int rc;  
    int line_x, line_y;  
    long int location = 0;
    char tmp[1024*10];
	static unsigned short b,g,r;
	static unsigned short rgb; /*2個字節*/
	PIXEL pix;  

 	fp = fopen( picname, "rb" );  
    if (fp == NULL)  
   		 {  
    		printf("open errror\n");
	        return( -1 );  
	    }  
  printf("Open OK \n");

  /* BITMAPFILEHEADER*/
   rc = fread( &FileHead, sizeof(BITMAPFILEHEADER),1, fp );  
    if ( rc != 1)  
    {  
        printf("read header error!\n");  
        fclose( fp );  
        return( -2 );  
    }  
printf("Read BITMAPFILEHEADER  OK\n");

    //檢測是否是bmp圖像  
    if (memcmp(FileHead.cfType, "BM", 2) != 0)  
    {  
        printf("it's not a BMP file\n");  
        fclose( fp );  
        return( -3 );  
    }  
/*BITMAPINFOHEADER*/
    rc = fread( (char *)&InfoHead, sizeof(BITMAPINFOHEADER),1, fp );  
    if ( rc != 1)  
    {  
        printf("read infoheader error!\n");  
        fclose( fp );  
        return( -4 );  
    }  
  printf("Read BITMAPINFOHEADER  OK\n");
  
    	//跳轉的數據區  
    fseek(fp, FileHead.cfoffBits, SEEK_SET);  
    
    	//向framebuffer中寫BMP圖片  rgb高位有效
  	for  (line_y = 0; line_y<yres; line_y++)
   	 	for (line_x = 0; line_x<xres; line_x++)
   	 		{
   	 	       rc = fread(&pix , sizeof(PIXEL),1, fp);
			  	location = line_x*2+(yres-line_y)*xres*2;
   	 			r=((pix.red>>3)<<11)&0xfb80;
				g=((pix.green>>2)<<5)&0x07e0;
				b=(pix.blue>>3)&0x001f;
				rgb=r|g|b;
				*((unsigned short *)(fb_addr+location)) = rgb;
  		 	}
    fclose( fp );  
    return  0 ;  
 }  

int main(int argc, char *argv[ ])
{
      int fbfd,fb_size ;	  
     struct   fb_var_screeninfo  vinfo;   /*記錄用戶可修改的顯示控制參數*/
     struct fb_fix_screeninfo finfo;    /*取得緩衝區的物理地址*/

	// 打開/dev/fb*設備文件
      fbfd = open("/dev/fb0",  O_RDWR|O_CREAT, S_IRWXU); 	
      if (fbfd <0 )
	      	{ 
	      		printf("open error\n");
				exit(1);
    	  	}
	
	//需要的 屏幕內存空間的字節數	,取得顯示屏幕參數
	if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo))
		{  
			   printf("Error reading variable information.\n");  
		  	   exit(1);  
		 }  

   
   if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))
	     {  
			 printf("Error reading variable information.\n");	
			 exit(1);  
		}  
  printf("R:%d,G:%d,B:%d \n", vinfo.red, vinfo.green, vinfo.blue );  
  printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );	
  
	xres=vinfo.xres;  		/*可見解析度*/
   	yres=vinfo.yres;   	
    bits_per_pixel=vinfo.bits_per_pixel;  /* 每像素位數*/ 
	fb_size=xres*yres*bits_per_pixel/8;   /*計算屏幕的總大小（字節)*/ 

// fd的內存地址空間映射到我們的程序地址空間
// void *mmap(void *start, size_t length, int prot, int flags,int fd, off_t offset);
  if ( (fb_addr  = (char *)mmap( 0, fb_size, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0) )<0)
  	{
  		printf( "mmap error\n" );
		exit(1);
  	}
  
   printf("show_bmp\n");
   show_bmp( argv[1] );

     //刪除對象映射  
   munmap(fb_addr, fb_size);  
   close(fbfd); 	

   return 0;
}

執行開發板程序：

圖片顯示：