一、下载源码包
二、创建安装并解压
mkdir ~/libjpeg
tar -zxvf jpegsrc.v9d.tar.gz三、移植、编译并安装
cd jpeg-9d/
./configure --host=arm-none-linux-gnueabi --prefix=${HOME}/libjpeg
make
make install四、图片缩放处理
#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/input.h>
#include <sys/mman.h>
#include "jpeglib.h" //开发者指定头文件路径
#include <setjmp.h>
int lcd_fd;
int*lcd_ptr;
unsigned char lcd_buf[800*480*4] = {0};
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;
/*
* Here's the routine that will replace the standard error_exit method:
*/
int lcd_draw_point(int i, int j, int color)
{
*(lcd_ptr+800*j+i) = color;
}
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);
}
/*
* Sample routine for JPEG decompression. We assume that the source file name
* is passed in. We want to return 1 on success, 0 on error.
*/
// 800 480 400 240 居中
int lcd_draw_jpeg(int x, int y, const char *filename, char *jpeg_buf, int jpeg_size, int zoom_flag)
{
/* This struct contains the JPEG decompression parameters and pointers to
* working space (which is allocated as needed by the JPEG library).
*/
struct stat statbuf;
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 my_error_mgr jerr;
int x_c = x;
/* More stuff */
//FILE * infile; /* source file */
JSAMPARRAY buffer; /* Output row buffer */
int row_stride; /* physical row width in output buffer */
unsigned char *argb_buf = lcd_buf;
/* 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.
*/
int img_fd;
char* img_buf;
int img_size;
if (filename != NULL) {
int img_fd = open(filename, O_RDWR);
if (img_fd == -1) {
printf("open file failed\n");
return -1;
}
fstat(img_fd, &statbuf);
img_size = statbuf.st_size;
img_buf = calloc(1, img_size);
read(img_fd, img_buf, img_size);
}else {
img_buf = jpeg_buf;
img_size = jpeg_size;
}
/* Step 1: 分配并初始化jpeg解压对象和错误处理对象 */
/* We set up the normal JPEG error routines, then override error_exit. */
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = my_error_exit;
/* Establish the setjmp return context for my_error_exit to use. */
if (setjmp(jerr.setjmp_buffer)) {
/* If we get here, the JPEG code has signaled an error.
* We need to clean up the JPEG object, close the input file, and return.
*/
jpeg_destroy_decompress(&cinfo);
close(img_fd);
return 0;
}
/* Now we can initialize the JPEG decompression object. */
jpeg_create_decompress(&cinfo);
/* Step 2: 指定解压数据源 (eg, 文件) */
jpeg_mem_src(&cinfo, img_buf, img_size);
/* Step 3: 读取文件信息数据 */
(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: 设置解压参数 */
/* In this example, we don't need to change any of the defaults set by
* jpeg_read_header(), so we do nothing here.
*/
/* 缩小一倍*/
cinfo.scale_num = 1;
cinfo.scale_denom = zoom_flag;
/* 放大一倍
cinfo.scale_num = 2;
cinfo.scale_denom = 1;*/
/* Step 5: 开始解压 */
(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 = (*cinfo.mem->alloc_sarray)
((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
int color, r, g, b, i;
/* Step 6: 取出数据 */
/* 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.
*/
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, (JSAMPARRAY)&argb_buf, 1);
for (i = 0; i < cinfo.output_width; i++) {
b = *(argb_buf+2);
g = *(argb_buf+1);
r = *(argb_buf+0);
//合并
color = b;
color |= (g << 8);
color |= (r << 16);
lcd_draw_point(x, y, color);
argb_buf+=3;
x++;
}
y++;
x = x_c;
}
/* Step 7: 完成解压 */
(void) jpeg_finish_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
/* Step 8: 释放资源 */
/* 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...)
*/
if (filename != NULL) {
close(img_fd);
}
/* 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 0;
}
int main(void)
{
//1,打开设备文件
int lcd_fd = open("/dev/fb0", O_RDWR);
//错误处理
if (lcd_fd == -1) {
printf("open lcd device failed!\n");
return -1;
}
//2,为lcd设备建立内存映射关系
lcd_ptr = mmap(NULL, 800*480*4, PROT_READ | PROT_WRITE, MAP_SHARED, lcd_fd, 0);
if (lcd_ptr == MAP_FAILED) {
printf("mmap failed!\n");
return -1;
}
//lcd_draw_jpeg(起点位置x,起点位置y,图片名字,动态图像数据缓冲区，动态数据的大小，缩放比例);
//eg : lcd_draw_jpeg(0,0 "1.jpg", NULL, 0, 1);
//解除映射
munmap(lcd_ptr, 800*480*4);
//b 关闭设备文件
close(lcd_fd);
return 0;
}编写完后进行编译运行：
arm-linux-gcc jpeg2lcd.c -o jpeg2lcd -I ~/libjpeg/include/ -L ~/libjpeg/lib -ljpeg五、扩展
-I（大写i） 指定头文件路径
-L （大写l）指定库文件路径
-l （小写l）链接库文件