libjpeg framebufer 代码自己敲了一遍 （九）

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 对照着  使用libjpeg显示JPEG图像在framebuffer 测试（八）  这个代码，自己敲了一遍，这样理解就更快了，对其中的代码进行的注释。实现一样的功能

代码附件： jpeg-press-self.rar  

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <jpeglib.h>
#include <jerror.h>

#define FB_DEV "/dev/fb0"

void    usage(char *msg);
unsigned short RGB888_to_RGB565(unsigned char red,unsigned char green,unsigned char blue);
int     fb_open(char *fb_device);
int     fb_close(int fd);
int     fb_stat(int fd,int *width,int *height,int *depth);
void     *fb_mmap(int fd,unsigned screensize);
int     fb_munmap(void *start,size_t length);
int     fb_pixel(void *fbmem,int width,int height,int x,int y,unsigned short color);


int main(int argc,char *argv[])
{
    struct jpeg_decompress_struct cinfo;  //解码结构体
    struct jpeg_error_mgr jerr;
    FILE     *infile;
    unsigned char *buffer;

    FBDEV *fr_dev;
    int fbdev;        //fbdev=open("/dev/fb0");
    char *fb_device; //fb_device=getenv("FRAMEBUFFER");取得FRAMEBUFFER环境变量
    unsigned char *fbmem;
    unsigned int screensize;
    unsigned int fb_width;
    unsigned int fb_height;
    unsigned int fb_depth;
    unsigned int x;
    unsigned int y;

    if (argc!=2)  //输入一个变量
    {
        usage("insuffient auguments");
        exit(-1);
    }

    init_framebuffer(&fr_dev);

    if((fb_device=getenv("FRAMEBUFFER"))==NULL)   //打开 /dev/fb0 缓冲帧
        fb_device=FB_DEV;//="/dev/fb0"
    fbdev=fb_open(fb_device);

    fb_stat(fbdev,&fb_width,&fb_height,&fb_depth);  //获取 LCD 可变/固定参数

    screensize=fb_width*fb_height*fb_depth/8;

    fbmem=fb_mmap(fbdev,screensize);  //映射地址


    if((infile=fopen(argv[1],"rb"))==NULL)    //打开 解码图片
    {
        fprintf(stderr,"open %s failed \n",argv[1]);
        exit(-1);
    }

    cinfo.err=jpeg_std_error(&jerr);  //设置 错误处理
    jpeg_create_decompress(&cinfo);   //初始化 解码 结构体
    jpeg_stdio_src(&cinfo,infile);    //输入 解码 图片
    jpeg_read_header(&cinfo,TRUE);    //读 jpeg 头
    jpeg_start_decompress(&cinfo);    //开始 解码

    if((cinfo.output_width>fb_width)||(cinfo.output_height>fb_height))  //判断图片大小
    {
        printf("too large JPEG file,cannot display\n");
        return -1;
    }

    buffer=(unsigned char *)malloc(cinfo.output_width*cinfo.output_components);
    y=0;
    while(cinfo.output_scanline<cinfo.output_height)
    {
        jpeg_read_scanlines(&cinfo,&buffer,1);
        if(fb_depth==16)
        {
            unsigned short color;
            for(x=0;x<cinfo.output_width;x++)
            {
                color=RGB888_to_RGB565(buffer[3*x],buffer[3*x+1],buffer[3*x+2]);
                fb_pixel(fbmem,fb_width,fb_height,x,y,color);
            }
        }
        else if(fb_depth==24)
        {
            memcpy((unsigned char *)fbmem+y*fb_width*3,buffer,cinfo.output_width*cinfo.output_components);

        }

        y++;  //next scanline
    }

    jpeg_finish_decompress(&cinfo);
    jpeg_destroy_decompress(&cinfo);
    free(buffer);
    fclose(infile);

    fb_munmap(fbmem,screensize);
    fb_close(fbdev);

    return 0;
}


int fb_stat(int fb,int *width,int *height,int *depth)
{
    struct fb_fix_screeninfo fb_finfo;
    struct fb_var_screeninfo fb_vinfo;
    if(ioctl(fb,FBIOGET_FSCREENINFO,&fb_finfo))
    {
        perror(__func__);
        return (-1);
    }

    if(ioctl(fb,FBIOGET_VSCREENINFO,&fb_vinfo))
    {
        perror(__func__);
        return (-1);
    }

    *width=fb_vinfo.xres;
    *height=fb_vinfo.yres;
    *depth=fb_vinfo.bits_per_pixel;
    return 0;
}

void *fb_mmap(int fb,unsigned int screensize)
{
    caddr_t fbmem;  //typedef void *caddr_t;
    if((fbmem=mmap(NULL,screensize,PROT_READ|PROT_WRITE,MAP_SHARED,fb,0))==MAP_FAILED)
    {
        perror(__func__);
        return (void *)(-1);
    }
    return (fbmem);
}

void usage(char *msg)
{
    fprintf(stderr,"%s\n",msg);
    printf("Usage:fv some-jpeg-filee.jpg\n");
}

unsigned short RGB888_to_RGB565(unsigned char red,unsigned char green,unsigned char blue)
{
    unsigned short B= (blue>>3)&0x001F;
    unsigned short G= ((green>>2)<<5)&0x07E0;
    unsigned short R= ((red>>3)<<11)&0xF800;
    return (unsigned short)(R|G|B);
}

int fb_open(char *fb_device)
{
    int fb;
    if((fb=open(fb_device,O_RDWR))<0)
    {
        perror(__func__);
        return -1;
    }
    return fb;
}

int fb_munmap(void *start,size_t length)
{
    return (munmap(start,length));
}


int fb_close(int fb)
{
    return(close(fb));
}

int fb_pixel(void *fbmem,int width,int height,int x,int y,unsigned short color)
{
    if((x>width)||(y>height))
        return -1;

    unsigned short *dst=((unsigned short *)fbmem+y*width+x);
    *dst=color;
    return 0;
}