一、有关配置
这个库的移植可以说是，很简单，直接使用CubMAX工具就可以帮我们生成移植好的代码，如果你想移植到其他平台，将CubMAX生成的那几个文件拷到你的工程里面就可以了。主要是这个如何使用起来，其实也不难，就是注意好细节接可以了。
二、编写解码函数
struct my_error_mgr {
struct jpeg_error_mgr pub; /* "public" fields */
jmp_buf setjmp_buffer; /* for return to caller */
};
typedef struct my_error_mgr * my_error_ptr;METHODDEF(void)
my_error_exit (j_common_ptr cinfo)
{
/* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
my_error_ptr myerr = (my_error_ptr) cinfo->err;
/* Always display the message. */
/* We could postpone this until after returning, if we chose. */
(*cinfo->err->output_message) (cinfo);
/* Return control to the setjmp point */
longjmp(myerr->setjmp_buffer, 1);
}int read_JPEG_file (char * filename)
{
struct jpeg_decompress_struct cinfo;
struct my_error_mgr jerr;
//
JFILE fil; /* target file */ 这个其实就是文件系统里面的那个FILE
JSAMPARRAY buffer; /* pointer to JSAMPLE row[s] */
int row_stride; /* physical row width in image buffer */
FRESULT res; //文件打开的返回参数
uint16_t i = 0;
//打开文件
if ((res = f_open(&fil, filename, FA_READ)) != 0)
{
printf("can't open %s, res = %d\n", filename, res);
return -1;
}
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = my_error_exit;
if (setjmp(jerr.setjmp_buffer))
{
jpeg_destroy_decompress(&cinfo);
f_close(&fil);
return -1;
}
//解码器作必要的内存分配 和数据结构的初始化
jpeg_create_decompress(&cinfo);
//将打开的原JPEG图片和我们的解码器相关联
jpeg_stdio_src(&cinfo, &fil);
(void) jpeg_read_header(&cinfo, TRUE);
//启动解码器
(void) jpeg_start_decompress(&cinfo);
row_stride = cinfo.output_width * cinfo.output_components;
buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr)&cinfo, JPOOL_IMAGE, row_stride, 1);
while (cinfo.output_scanline < cinfo.output_height)
{
jpeg_read_scanlines(&cinfo, buffer, 1); //读取解码后的数据 一次读一行
for(i=0; i<row_stride; i+=3) //发送整个jpg文件
{
while((USART1->SR&0X40)==0); //循环发送,直到发送完毕
USART1->DR = *((buffer[0])+i);
}
}
//解码结束做清理工
jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
f_close(&fil);
return 0;
}需要注意的就是，里面的文件打开函数和关闭函数，都是你的文件系统里面提供的函数，也就是说不同的文件系统你这个可能是不一样的，我使用的的FATFS文件管理系统。我这里给你代码不全，其他的没有必要这里给的都是重点，其他的它的源码里面有一个example.c文件里面就是示例代码，我这个也是按照这个改的。
三、注意事项
花了一天吸取的经验教训，如果你发现你的程序无缘无故就死了，一定要注意处理的图片不要太大，我刚开始处理的是480*800的RGB888的一张图片，然后程序就无缘无故的死了，这个受影响的主要是图片的宽和高，最后查找一圈才发现给的图片太大了，内部再申请内存的时候申请不到，就死了。也可以修改堆的大小，还可以使用外部SRAM，将内存分配到外步SRAM中。他这个解码库是会申请内存的，这一点很重要。所以移植的时候这个也要注意。下面的代码时那个工具帮我生成的移植好的代码。还有就是出了问题一定不要先怀疑这个库，先从自己的代码中找问题，还有一点就是栈和堆的内存空间你要从新分配一下；如果你使用的不是这个工具那么你就要在起始文件里面去找。
/* USER CODE BEGIN Header */
/**
******************************************************************************
* File Name : jdata_conf.c
* Description : This file implements LibJPEG file based read/write functions.
*
******************************************************************************
* @attention
*
* Copyright (c) 2019 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
**/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
/*FatFS is chosen for File storage*/
#include "jdata_conf.h"
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* Private function prototypes -----------------------------------------------*/
/* Private functions ---------------------------------------------------------*/
size_t read_file (FIL *file, uint8_t *buf, uint32_t sizeofbuf)
{
static size_t BytesReadfile ;
f_read (file, buf , sizeofbuf, &BytesReadfile);
return BytesReadfile;
}
size_t write_file (FIL *file, uint8_t *buf, uint32_t sizeofbuf)
{
static size_t BytesWritefile;
f_write (file, buf , sizeofbuf, &BytesWritefile);
return BytesWritefile;
}
/* USER CODE BEGIN Header */
/**
******************************************************************************
* File Name : jdata_conf.h
* Description : This file provides header to "jdata_conf.h" module.
* It implements also file based read/write functions.
*
******************************************************************************
* @attention
*
* Copyright (c) 2019 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
**/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
/*FatFS is chosen for File storage*/
#include "ff.h"
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
/* Private function prototypes -----------------------------------------------*/
/* Private functions ---------------------------------------------------------*/
/*This defines the memory allocation methods.*/
#define JMALLOC malloc
#define JFREE free
/*This defines the File data manager type.*/
#define JFILE FIL
size_t read_file (FIL *file, uint8_t *buf, uint32_t sizeofbuf);
size_t write_file (FIL *file, uint8_t *buf, uint32_t sizeofbuf) ;
#define JFREAD(file,buf,sizeofbuf) \
read_file (file,buf,sizeofbuf)
#define JFWRITE(file,buf,sizeofbuf) \
write_file (file,buf,sizeofbuf)
