framebuffer下用libjeg库显示jpeg图片

说明：编译时加上-ljpeg

源代码如下：

/*
 * =====================================================================================
 *
 *       Filename:  digital_frame.c
 *
 *    Description:  framebuffer下用libjeg库显示jpeg图片
 *
 *        Version:  1.0
 *        Created:  2011年03月21日 14时01分21秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  [e-mail]
 *
 * =====================================================================================
 */
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define FB_DEV      "/dev/fb0"
#define JPEG        0x001
#define PNG     0x010
#define BMP     0x100
#define UNKNOWN     0x111
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 color
{
    unsigned char r;
    unsigned char g;
    unsigned char b;
}COLOR;;
typedef struct 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:[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);
    fbmem = mmap(0, screen_w * screen_h * screen_bits / 8, PROT_READ | PROT_WRITE, MAP_SHARED, fb_dev, 0);
    return;
}
//判断图片格式
int judge_picture_mode(char **argv)
{
    char header[8];
    printf("picture = %s/n", argv[1]);
    infile = fopen(argv[1], "rb");
    if(infile == NULL)
    {
        printf("Error:open %s error!/n", argv[1]);
        exit(1);
    }
    memset(header, 0, sizeof(header));
    fread(&header, 8, 1, infile);
    fseek(infile, -8, 1);
    if((unsigned char)header[0] == 0xff)
    {
        return JPEG;
    }
    else if((unsigned char)header[0] == 0x89)
    {
        return PNG;
    }
    else if(0 == strncmp(header, "BM", 2))
    {
        return BMP;
    }
    else
    {
        return UNKNOWN;
    }
}
//显示jpg/jpeg格式图片
void display_jpeg()
{
    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;
    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("picture info:/n");
    printf("width  = %d/n", picture_w);
    printf("height = %d/n", picture_h);
    printf("bits   = %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;
}
int main(int argc, char* argv[])
{
    int picture_mode;
    if(argc != 2)
    {
        printf("Usage:[sudo ./digital_frame xxx.jpg]/n");
        exit(1);
    }
    //fb0初始化
    fb_init();
    //判断图片格式
    picture_mode = judge_picture_mode(argv);
    switch(picture_mode)
    {
        case JPEG:
            printf("JPEG/JPG/n");
            display_jpeg();
            break;
        case PNG:
            printf("PNG/n");
            break;
        case BMP:
            printf("bmp/n");
            break;
        case UNKNOWN:
            printf("UNKNOWN/n");
            break;
        default:
            break;
    }
    return 0;
}