BMP图像解析显示

首先获取bmp文件信息头，根据得到的图像长，宽，以及存储位数信息，设置输出，将其输出到屏幕上。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <linux/fb.h>
#include <unistd.h>
#include <jpeglib.h>
#define FB_DEV "/dev/fb0"

static int fb_dev;
static struct   fb_var_screeninfo fb_var;
static int screen_w, screen_h, screen_bits;
static void *fbmem, *data;
static FILE *infile;


typedef struct
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
}COLOR;;
typedef struct
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
    unsigned char a;
}PIXEL_T;
//BMP的内容
typedef struct bmp_file_header
{
    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]; //位图阵列相对与文件头的偏移量（字节）
}__attribute__((packed)) BITMAPFILEHEADER; //文件头结构
typedef struct bmp_info_header
{
    char ciSize[4]; //sizeof 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
}__attribute__((packed)) BITMAPINFOHEADER; //位图信息头结构

unsigned char *fbp;
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;

long int screensize;
int xres = 0;
int yres = 0;
int bits_per_pixel = 0;

//初始化fb0
void fb_init()
{
    //打开fb0设备文件
    fb_dev = open(FB_DEV, O_RDWR);
    if(fb_dev < 0)
    {
        printf("Error:open %s error/n", FB_DEV);
        printf("Usage:[sudo ./digital_frame xxx.jpg]/n");
        exit(1);
    }
    //获取fb0参数
    ioctl(fb_dev, FBIOGET_VSCREENINFO, &fb_var);
    screen_w = fb_var.xres;
    screen_h = fb_var.yres;
    screen_bits = fb_var.bits_per_pixel;
    printf("Framebuffer:%d * %d/n", screen_w, screen_h);
    printf("screen_bits:%d/n", screen_bits);

    int screensize=screen_w * screen_h * screen_bits / 8;
    fbmem = mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fb_dev, 0);


    int i=0,bgcolor=0;
    for(i=0;i<screensize;i+=fb_var.bits_per_pixel/8)
        {
            memcpy(fbmem+i,&bgcolor,fb_var.bits_per_pixel/8);
        }

    return;
}

//chartolong
long chartolong(char *string, int length)
{
    long number;
    if(length <= 4)
    {
        memset(&number, 0, sizeof(long));
        memcpy(&number, string, length);
    }
    return number;
}
//显示bmp格式图片
void display_bmp(char *bmpfile)
{
    BITMAPFILEHEADER FileHead;
    BITMAPINFOHEADER InfoHead;
    int rc ,i ,j, x, y;
    int ciWidth, ciHeight, ciBitCount;
    long int BytesPerLine = 0;
    COLOR picture_color;
    PIXEL_T **fbp;
    unsigned char *buffer, *tmpbuf;

    infile = fopen( bmpfile, "rb" );
    //读位图文件头
    rc = fread(&FileHead, sizeof(BITMAPFILEHEADER), 1, infile);
    if(rc != 1)
    {
        printf("Error:read bmp header error!\n");
        fclose(infile);
        exit(1);
    }

    //判断位图的类型
    if(memcmp(FileHead.cfType, "BM", 2) != 0)
    {
        printf("This is not a bmp picture!\n");
        fclose(infile);
        exit(1);
    }

    //读取位图信息头
    rc = fread((char *)&InfoHead, sizeof(BITMAPINFOHEADER), 1, infile);
    if(rc != 1)
    {
        printf("Error:read bmp infoheader error!\n");
        fclose(infile);
        exit(1);
    }
    ciWidth = (int)chartolong(InfoHead.ciWidth, 4);
    ciHeight = (int)chartolong(InfoHead.ciHeight, 4);
    ciBitCount = (int)chartolong(InfoHead.ciBitCount, 4);
    fseek(infile, (int)chartolong(FileHead.cfoffBits, 4), SEEK_SET);
    BytesPerLine = (ciWidth * ciBitCount + 31) / 32 * 4;

    printf("图像宽度：%d\n",ciWidth);
    printf("图像高度：%d\n",ciHeight);
    printf("每个像素位数：%d\n",ciBitCount);


    fbp = (PIXEL_T **)malloc(sizeof(PIXEL_T *) * screen_w);
    for(i = 0, x = 0 * screen_bits / 8, y = 0; i < screen_w; i++)
    {
        fbp[i] = (PIXEL_T *)(fbmem + (y + i) * screen_w * screen_bits / 8 + x);
    }
    buffer = (unsigned char *)malloc(BytesPerLine);
    memset(buffer, 0, BytesPerLine);
    for(i = ciHeight - 1; i >= 0; i--)
    {
        tmpbuf = buffer;
        rc = fread(tmpbuf, BytesPerLine, 1, infile);

        for(j = 0; j < ciWidth; j++)
        {
            memcpy(&picture_color, tmpbuf, ciBitCount / 8);

            fbp[i][j].r = picture_color.r;
            fbp[i][j].g = picture_color.g;
            fbp[i][j].b = picture_color.b;
            tmpbuf += ciBitCount / 8;
        }
    }

    fclose(infile);
    return;
}


int main(int argc, char* argv[])
{

    if(argc != 2)
    {
        printf("Usage:[ + xxx.bmp]\n");
        exit(1);
    }
    //fb0初始化
    fb_init();

    display_bmp(argv[1]);
    return 0;
}