jpeg图像解码显示

jpeg图像为解压后即得到位图数据，与上一篇中的bmp图像显示相比，增加的步骤是需要运用jpeg库提供的解码函数，解码得到图像数据，然后再把原始图像显示出来。

#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;
//JPEG的内容
typedef struct jpeg_color
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
}COLOR;;
typedef struct jpeg_pixel_t
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
    unsigned char a;
}PIXEL_T;

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

    int screensize=screen_w * screen_h * screen_bits / 8;
    int i=0,bgcolor=0;
    for(i=0;i<screensize;i =fb_var.bits_per_pixel/8) //清屏
        {
            memcpy(fbmem i,&bgcolor,fb_var.bits_per_pixel/8);
        }

    return;
}

//显示jpg/jpeg格式图片
void display_jpeg(char *jpegfile)
{
    struct jpeg_decompress_struct cinfo;
    struct jpeg_error_mgr jerr;
    int picture_w, picture_h, picture_bits;
    int i, j, x, y;
    unsigned char *buffer, *tmpbuf;
    COLOR picture_color;
    PIXEL_T **fbp;

    infile = fopen(jpegfile, "rb" );

    fbp = (PIXEL_T **)malloc(sizeof(PIXEL_T *) * screen_w);
    //x, y 代表图片的起始坐标
    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);
    }
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_decompress(&cinfo);
    //指定要解压缩的图像文件
    jpeg_stdio_src(&cinfo, infile);
    //获取图像信息
    jpeg_read_header(&cinfo, TRUE);
    //开始解压
    jpeg_start_decompress(&cinfo);
    picture_w = cinfo.output_width;
    picture_h = cinfo.output_height;
    picture_bits = cinfo.output_components;

    printf("图片信息:\n");
    printf("宽度  = %d\n", picture_w);
    printf("高度 = %d\n", picture_h);
    printf("位数   = %d\n", picture_bits);

    //获取颜色值
    buffer = (unsigned char *)malloc(picture_w * picture_bits);
    memset(buffer, 0, picture_w * picture_bits);
    for(i = 0; i < picture_h; i )
    {
        tmpbuf = buffer;
        jpeg_read_scanlines(&cinfo, &tmpbuf, 1);
        for(j = 0; j < picture_w; j )
        {
            memcpy(&picture_color, tmpbuf, sizeof(picture_color));
            fbp[i][j].b = picture_color.r;
            fbp[i][j].g = picture_color.g;
            fbp[i][j].r = picture_color.b;
            tmpbuf = picture_bits;
        }
    }
    //完成解压
    jpeg_finish_decompress(&cinfo);
    //释放解压对象
    jpeg_destroy_decompress(&cinfo);
    free(buffer);
    return;
}

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

int main(int argc, char* argv[])
{
    if(argc != 2)
    {
        printf("Usage:[ xxx.jpg]\n");
        exit(1);
    }
    //fb0初始化
    fb_init();

    display_jpeg(argv[1]);
    fclose(infile);
    return 0;
}