文件IO-在屏幕上显示jpeg格式的图片

在屏幕上指定位置显示jpeg格式的图片，像素存储格式为rgb

/********************************************************************************
*
*
* 显示jpeg格式图片在屏幕指定位置
* author：jindouliu2024@163.com 
* date：2025.4.19
* 
*
* Copyright (c)  2024-2025   jindouliu2024@163.com   All right Reserved
* ********************************************************************************/

#include <stdio.h>
#include <fcntl.h> 
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<stdbool.h>
#include <sys/mman.h>
#include "jpeglib.h"

int read_JPEG_file (char * filename,int x,int y)
{
  /* This struct contains the JPEG decompression parameters and pointers to
   * working space (which is allocated as needed by the JPEG library).
   */
 	 struct jpeg_decompress_struct cinfo;
  /* We use our private extension JPEG error handler.
   * Note that this struct must live as long as the main JPEG parameter
   * struct, to avoid dangling-pointer problems.
   */
  	
	struct jpeg_error_mgr jerr;
  /* More stuff */
  FILE * infile;		/* source file */
  unsigned char * buffer;		/* Output row buffer */
  int row_stride;		/* physical row width in output buffer */

  /* In this example we want to open the input file before doing anything else,
   * so that the setjmp() error recovery below can assume the file is open.
   * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
   * requires it in order to read binary files.
   */

  if ((infile = fopen(filename, "rb")) == NULL) {
    fprintf(stderr, "can't open %s\n", filename);
    return 0;
  }

  /* Step 1: allocate and initialize JPEG decompression object */

  /* We set up the normal JPEG error routines, then override error_exit. */
 	
 	cinfo.err = jpeg_std_error(&jerr);
  	
  /* Establish the setjmp return context for my_error_exit to use. */
 
  /* Now we can initialize the JPEG decompression object. */
  jpeg_create_decompress(&cinfo);

  /* Step 2: specify data source (eg, a file) */

  jpeg_stdio_src(&cinfo, infile);

  /* Step 3: read file parameters with jpeg_read_header() */

  (void) jpeg_read_header(&cinfo, TRUE);
  /* We can ignore the return value from jpeg_read_header since
   *   (a) suspension is not possible with the stdio data source, and
   *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
   * See libjpeg.txt for more info.
   */

  /* Step 4: set parameters for decompression */

  /* In this example, we don't need to change any of the defaults set by
   * jpeg_read_header(), so we do nothing here.
   */

  /* Step 5: Start decompressor */

  (void) jpeg_start_decompress(&cinfo);
  /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

  /* We may need to do some setup of our own at this point before reading
   * the data.  After jpeg_start_decompress() we have the correct scaled
   * output image dimensions available, as well as the output colormap
   * if we asked for color quantization.
   * In this example, we need to make an output work buffer of the right size.
   */ 
  /* JSAMPLEs per row in output buffer */
  row_stride = cinfo.output_width * cinfo.output_components;
  /* Make a one-row-high sample array that will go away when done with image */
  buffer = (char *)calloc(1,row_stride);
  int lcd_dp = open("/dev/fb0",O_RDWR);
  /* Step 6: while (scan lines remain to be read) */
  /*           jpeg_read_scanlines(...); */

  /* Here we use the library's state variable cinfo.output_scanline as the
   * loop counter, so that we don't have to keep track ourselves.
   */
  short data=0;
  int i=0;
  short *lcd_mp = (short *)mmap(NULL,1024*600*2,PROT_READ|PROT_WRITE,MAP_SHARED,lcd_dp,0);
  while (cinfo.output_scanline < cinfo.output_height) {
    /* jpeg_read_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could ask for
     * more than one scanline at a time if that's more convenient.
     */
    
    (void) jpeg_read_scanlines(&cinfo, &buffer, 1);
		//按宽度扫描
		for(int width = 0;width < cinfo.output_width;width++){
			//写入像素值
			data = (buffer[width*3+2]/8)|((buffer[width*3+1]/4)<<5)|((buffer[width*3]/4)<<11);//针对位深为2的屏幕
			*(lcd_mp+1024*x+y+1024*(cinfo.output_scanline-1)+width) = data;
			i+=3;
			data = 0;
		}
	
	
	
  }
	//关闭屏幕文件并解除内存映射
	munmap(lcd_mp,1024*600*2);
  /* Step 7: Finish decompression */

  (void) jpeg_finish_decompress(&cinfo);
  /* We can ignore the return value since suspension is not possible
   * with the stdio data source.
   */

  /* Step 8: Release JPEG decompression object */

  /* This is an important step since it will release a good deal of memory. */
  jpeg_destroy_decompress(&cinfo);

  /* After finish_decompress, we can close the input file.
   * Here we postpone it until after no more JPEG errors are possible,
   * so as to simplify the setjmp error logic above.  (Actually, I don't
   * think that jpeg_destroy can do an error exit, but why assume anything...)
   */
  fclose(infile);

  /* At this point you may want to check to see whether any corrupt-data
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
   */

  /* And we're done! */
  return 1;
}

int main(int argc,char *argv[])
{
	read_JPEG_file (argv[1],200,100);
	return 0;
}