本文最后更新于 161 天前，其中的信息可能已经有所发展或是发生改变。
#include <stdio.h>
#include <setjmp.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include </home/gec/software/installed/jepg/include/jpeglib.h>
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);
}
GLOBAL(int)
read_JPEG_file (char * filename,int* lcd_buf,const char* x_start,const char* y_start)
{
struct jpeg_decompress_struct cinfo;
struct my_error_mgr jerr;
/* More stuff */
FILE * infile; /* source file */
JSAMPARRAY buffer; /* Output row buffer */
int row_stride; /* physical row width in output buffer */
if ((infile = fopen(filename, "rb")) == NULL) {
fprintf(stderr, "can't open %s\n", filename);
return 0;
}
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = my_error_exit;
if (setjmp(jerr.setjmp_buffer)) {
jpeg_destroy_decompress(&cinfo);
fclose(infile);
return 0;
}
jpeg_create_decompress(&cinfo);
jpeg_stdio_src(&cinfo, infile);
(void) jpeg_read_header(&cinfo, TRUE);
(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);
// 在 while 循环外定义一个 y，用于记录当前正在处理屏幕的第几行
int y = 0;
int xnum = atoi(x_start);
int ynum = atoi(y_start);
while (cinfo.output_scanline < cinfo.output_height) {
// 每次读取 1 行数据，存入 buffer 中
(void) jpeg_read_scanlines(&cinfo, buffer, 1);
// buffer[0] 指向的就是刚刚解码出来的这一行 RGB 数据
unsigned char *row_data = buffer[0];
// 遍历这一行的每一个像素
for (int x = 0; x < cinfo.output_width; x++) {
// 【关键保护伞】：防止图片尺寸大于屏幕导致段错误越界
if (x < 800 && y < 480 && ynum < 480 - cinfo.output_height && xnum < 800 - cinfo.output_width) {
// 依次取出 R, G, B 分量 (注意这里的顺序和 BMP 不同)
unsigned char r = row_data[x * 3 + 0];
unsigned char g = row_data[x * 3 + 1];
unsigned char b = row_data[x * 3 + 2];
// 拼装成 LCD 需要的 32位 ARGB 格式 (0x00RRGGBB)
int color = (r << 16) | (g << 8) | b;
// 写入内存映射的显存中
lcd_buf[(800*ynum+xnum)+(800 * y + x)] = color;
}else{
printf("图片刷新位置超过屏幕！\n");
printf("图片大小应小于800*480\n");
printf("图片刷新位置：x轴0~%d，y轴0~%d\n",799 - cinfo.output_width,479 - cinfo.output_height);
return 0;
}
}
// 一行处理完毕，行号 +1
y++;
}
(void) jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
fclose(infile);
return 1;
}
int main(int argc , char* argv[])
{
//参数检查
if(argc!=4)
{
printf("用法: %s <图片路径> <x轴坐标> <y轴坐标>\n", argv[0]);
return 0;
}
//打开lcd屏幕
int lcd = open("/dev/ubuntu_lcd",O_RDWR);
if(lcd == -1)
{
printf("lcd屏幕打开失败！\n");
return 0;
}
//内存映射
int* lcd_buf = mmap(NULL,800*480*4,PROT_READ|PROT_WRITE,MAP_SHARED,lcd,0);
if (lcd_buf == MAP_FAILED) {
perror("mmap");
close(lcd);
return 1;
}
//清除屏幕为白色
memset(lcd_buf,0xFFFFFFFF,800*480*4);
//读取jpeg信息并刷入内存
read_JPEG_file (argv[1],lcd_buf,argv[2],argv[3]);
//关闭设备，释放内存
close(lcd);
munmap(lcd_buf,800*480*4);
return 0;
}
