在LCD上的任意位置显示一张任意大小的jpg图片

/*************************************************
 *
 *   file name:lcdshowjpg.c
 *   author   :momolyl@126.com
 *   date     :2024/05/13
 *   brief    :完成libjpeg库的移植，并设计程序实现在LCD上的任意位置显示一张任意大小的jpg图片，注意不要越界。
 *   note     :None
 *
 *   CopyRight (c) 2024    momolyl@126.com    All Right Reseverd
 *
 **************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
/*
 * Include file for users of JPEG library.
 * You will need to have included system headers that define at least
 * the typedefs FILE and size_t before you can include jpeglib.h.
 * (stdio.h is sufficient on ANSI-conforming systems.)
 * You may also wish to include "jerror.h".
 */

#include "include/jpeglib.h"

int *lcd_mp;

// 成功返回1 失败返回0
int read_JPEG_file(char *filename, int start_x, int start_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);

  /* 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; // 计算一行的大小

  /* Make a one-row-high sample array that will go away when done with image */
  buffer = calloc(1, row_stride);

  /* 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.
   */
  int data = 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); // 从上到下，从左到右  RGB RGB RGB RGB

    for (int i = 0; i < cinfo.output_width; ++i) // 012 345
    {
      data |= buffer[3 * i] << 16;    // R
      data |= buffer[3 * i + 1] << 8; // G
      data |= buffer[3 * i + 2];      // B

      // 把像素点写入到LCD的指定位置
      lcd_mp[800 * start_y + start_x + 800 * (cinfo.output_scanline - 1) + i] = data;

      data = 0;
    }
  }

  /* 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 const *argv[])
{
  // 1.打开LCD   open
  int lcd_fd = open("/dev/fb0", O_RDWR);

  // 2.对LCD进行内存映射  mmap
  lcd_mp = (int *)mmap(NULL, 800 * 480 * 4, PROT_READ | PROT_WRITE, MAP_SHARED, lcd_fd, 0);

  // 3.显示一张jpg
  read_JPEG_file("demo.jpg", 267, 100);

  return 0;
}

运行结果：