display_bmp.c

在linux下通过framebuffer将bmp格式的图片画出来的程序。

/*
   showbmp.c
   allenyao 2006/11/3
*/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>

typedef struct
{
  char cfType[2];         /* 文件类型, 必须为 "BM" (0x4D42) */
  char cfSize[4];         /* 文件的大小(字节) */
  char cfReserved[4];     /* 保留, 必须为 0 */
  char cfoffBits[4];      /* 位图阵列相对于文件头的偏移量(字节) */
} BITMAPFILEHEADER;       /* 文件头结构 */

typedef struct
{
  char ciSize[4];         /* size of BITMAPINFOHEADER */
  char ciWidth[4];        /* 位图宽度(像素) */
  char ciHeight[4];       /* 位图高度(像素) */
  char ciPlanes[2];       /* 目标设备的位平面数, 必须置为1 */
  char ciBitCount[2];     /* 每个像素的位数, 1,4,8或24 */
  char ciCompress[4];     /* 位图阵列的压缩方法,0=不压缩 */
  char ciSizeImage[4];    /* 图像大小(字节) */
  char ciXPelsPerMeter[4];/* 目标设备水平每米像素个数 */
  char ciYPelsPerMeter[4];/* 目标设备垂直每米像素个数 */
  char ciClrUsed[4];      /* 位图实际使用的颜色表的颜色数 */
  char ciClrImportant[4]; /* 重要颜色索引的个数 */
} BITMAPINFOHEADER;       /* 位图信息头结构 */

typedef struct
{
  char rgbBlue;
  char rgbGreen;
  char rgbRed;
  char rgbReserved;
} RGBQUAD;

BITMAPFILEHEADER FileHead;
BITMAPINFOHEADER InfoHead;
RGBQUAD rgbquad;

char *fbp = 0;
int xres = 0;
int yres = 0;
int bits_per_pixel = 0;

int  show_bmp  ( char *bmpfile );
long chartolong( char * string, int length );
/******************************************************************************
*
******************************************************************************/
int main( int argc, char *argv[] )
{
    int err; 
    int fbfd = 0;
    struct fb_var_screeninfo vinfo;
    struct fb_fix_screeninfo finfo;
    long int screensize = 0;

    // Open the file for reading and writing
    fbfd = open("/dev/fb0", O_RDWR);
    if (!fbfd)
    {
        printf("Error cannot open framebuffer device.\n");
        exit(1);
    }

    // Get fixed screen information
    if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))
    {
        printf("Error reading fixed information.\n");
        exit(2);
    }

    // Get variable screen information
    if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo))
    {
        printf("Error reading variable information.\n");
        exit(3);
    }

    printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
    xres = vinfo.xres;
    yres = vinfo.yres;
    bits_per_pixel = vinfo.bits_per_pixel;

    // Figure out the size of the screen in bytes
    screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

    // Map the device to memory
    fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
                       fbfd, 0);
    if ((int)fbp == -1)
    {
        printf("Error&#58; failed to map framebuffer device to memory.\n");
        exit(4);
    }

     err = show_bmp( argv[1] );
      printf( "err nummber is %d\n",err );

    munmap(fbp, screensize);
    close(fbfd);
    return 0;
}

/******************************************************************************
*
******************************************************************************/
int show_bmp( char *bmpfile )
{
        FILE *fp;
        int rc;
        int ciBitCount, ciWidth, ciHeight;
        int line_x, line_y;
        long int location = 0, BytesPerLine = 0;
        char tmp[1024*10];
   
        /* 打开位图文件 */
        fp = fopen( bmpfile, "rb" );
        if (fp == NULL)
        {
                return( -1 );
        }
        
        /* 读取位图文件头 */
        rc = fread( &FileHead, 1, sizeof(BITMAPFILEHEADER), fp );
        if ( rc != sizeof( BITMAPFILEHEADER ) )
        {
                fclose( fp );
                return( -2 );
        }
        
        /* 判断位图的类型 */
        if (memcmp(FileHead.cfType, "BM", 2) != 0)
        {
                fclose( fp );
                return( -3 );
        }

        /* 读取位图信息头 */
        rc = fread( (char *)&InfoHead, 1, sizeof(BITMAPINFOHEADER), fp );
        if ( rc != sizeof(BITMAPINFOHEADER) )
        {
                fclose( fp );
                return( -4 );
        }
        
        ciWidth    = (int) chartolong( InfoHead.ciWidth,    4 );
        ciHeight   = (int) chartolong( InfoHead.ciHeight,   4 );
        ciBitCount = (int) chartolong( InfoHead.ciBitCount, 4 );
        
        line_x = line_y = 0;
        /*
        while( !feof( fp ) )
        {
                rc = fread( (char *)&rgbquad, 1, sizeof(RGBQUAD), fp );
                if ( rc != sizeof(RGBQUAD) )
                {
                        break;
                }

                location = line_x * bits_per_pixel / 8 + (ciHeight - line_y - 1) * xres * bits_per_pixel / 8;

                *(fbp + location) = rgbquad.rgbBlue;
                *(fbp + location + 1) = rgbquad.rgbGreen;
                *(fbp + location + 2) = rgbquad.rgbRed;
                *(fbp + location + 3) = rgbquad.rgbReserved;
                
                line_x++;
                if ( line_x == ( ciWidth - 1 ) )
                {
                        line_x = 0;
                        line_y++;
                }
        }
        */
        /*下面这句是从书上抄来的，我对它还有疑问？*/
        BytesPerLine = (ciWidth * ciBitCount + 31) / 32 * 4;
        
        while( !feof( fp ) )
        {
                rc = fread( tmp, 1, BytesPerLine, fp );
                if ( rc != BytesPerLine )
                {
                        break;
                }
                
                location = (ciHeight - line_y - 1) * xres * bits_per_pixel / 8;
                memcpy( (fbp + location) , tmp, BytesPerLine );

                line_y++;
        }
        fclose( fp );
        return( 0 );
}

/******************************************************************************
*
******************************************************************************/
long chartolong( char * string, int length )
{
        long number;
        
        if (length <= 4)
        {
                memset( &number, 0x00, sizeof(long) );
                memcpy( &number, string, length );
        }
        
        return( number );
}