参考EGui中的Demo程序显示JPG图像
对于JPG图像，好像是有专利问题……我并没有找到JPG图像格式详细说明。于是，参考EGui中的Demo程序，调用libjpeg.a库函数，在Framebuffer中显示JPG图像。在编译libjpeg.a时出了点错，“ar rc rc”多了一个“rc”！在成功编译后，把libjpeg.a及所有的.h文件都拷贝到程序目录中，就可以使用了。
showjpeg.c
/******************************************************************************
* showjpeg.c - 调用库函数对JPG文件进行解码, 并在framebuffer中显示出来
*
* Author : allen
* Email: [email protected]
* Date : 2006/11/20
******************************************************************************/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
char *fbp = 0;
int xres = 0;
int yres = 0;
int bits_per_pixel = 0;
extern unsigned char * decode_jpeg(char *filename, short *widthPtr, short *heightPtr);
intshow_jpg(char *bmpfile);
/******************************************************************************
*
******************************************************************************/
int main( int argc, char *argv[] )
{
int fbfd = 0;
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
long int screensize = 0;
if (argc != 2)
{
printf("usage: %s filename\n", argv[0]);
return 0;
}
// Open the file for reading and writing
fbfd = open("/dev/fb0", O_RDWR);
if (!fbfd)
{
printf("Error: cannot open framebuffer device.\n");
exit(1);
}
// Get fixed screen information
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))
{
printf("Error reading fixed information.\n");
exit(2);
}
// Get variable screen information
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo))
{
printf("Error reading variable information.\n");
exit(3);
}
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
xres = vinfo.xres;
yres = vinfo.yres;
bits_per_pixel = vinfo.bits_per_pixel;
// Figure out the size of the screen in bytes
screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;
// Map the device to memory
fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED,
fbfd, 0);
if ((int)fbp == -1)
{
printf("Error: failed to map framebuffer device to memory.\n");
exit(4);
}
show_jpg(argv[1]);
munmap(fbp, screensize);
close(fbfd);
return 0;
}
/******************************************************************************
*
******************************************************************************/
int show_jpg(char *filename)
{
int i, j;
short int width = 0, height = 0;
unsigned char *jpeg = NULL;
long location = 0, pos = 0;
jpeg = decode_jpeg(filename, &width, &height);
if (jpeg == NULL)
{
return -1;
}
/*显示图像信息*/
for (i=0; i<height; i++)
{
for (j=0; j<width; j++)
{
location = i * xres * bits_per_pixel / 8 + j * bits_per_pixel / 8;
pos = i * (width * 3) + (j * 3);
*(fbp + location + 0) = *(jpeg + pos + 2);
*(fbp + location + 1) = *(jpeg + pos + 1);
*(fbp + location + 2) = *(jpeg + pos + 0);
*(fbp + location + 3) = 0x00;
}
}
free(jpeg);
return 0;
}
jpeg.c
/*Copyright George Peter Staplin 2003*/
/*You may use/copy/modify/distribute this software for any purpose
*provided that I am given credit and you don't sue me for any bugs.
*/
/*Please contact me using [email protected] if you like this, or
*have questions.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "jpeglib.h"
#include "jerror.h"
#include <time.h>
#ifndef u_char
#define u_char unsigned char
#endif
void jpeg_error_exit (j_common_ptr cinfo) {
cinfo->err->output_message (cinfo);
exit (EXIT_FAILURE);
}
/*This returns an array for a 24 bit image.*/
u_char *decode_jpeg (char *filename, short *widthPtr, short *heightPtr)
{
register JSAMPARRAY lineBuf;
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr err_mgr;
int bytesPerPix;
FILE *inFile;
u_char *retBuf;
inFile = fopen (filename, "rb");
if (NULL == inFile)
{
printf ("Open file error %s\n",filename);
return NULL;
}
cinfo.err = jpeg_std_error (&err_mgr);
err_mgr.error_exit = jpeg_error_exit;
jpeg_create_decompress (&cinfo);
jpeg_stdio_src (&cinfo, inFile);
jpeg_read_header (&cinfo, 1);
cinfo.do_fancy_upsampling = 0;
cinfo.do_block_smoothing = 0;
jpeg_start_decompress (&cinfo);
*widthPtr = cinfo.output_width;
*heightPtr = cinfo.output_height;
bytesPerPix = cinfo.output_components;
lineBuf = cinfo.mem->alloc_sarray ((j_common_ptr) &cinfo, JPOOL_IMAGE, (*widthPtr * bytesPerPix), 1);
retBuf = (u_char *) malloc (3 * (*widthPtr * *heightPtr));
if (NULL == retBuf)
{
perror (NULL);
return NULL;
}
if (3 == bytesPerPix)
{
int x;
int y;
int i;
for (y = 0; y < cinfo.output_height; ++y)
{
jpeg_read_scanlines (&cinfo, lineBuf, 1);
memcpy ((retBuf + y * *widthPtr * 3),lineBuf[0],3 * *widthPtr);
}
} else if (1 == bytesPerPix)
{
unsigned int col;
int lineOffset = (*widthPtr * 3);
int lineBufIndex;
int x ;
int y;
for (y = 0; y < cinfo.output_height; ++y)
{
jpeg_read_scanlines (&cinfo, lineBuf, 1);
lineBufIndex = 0;
for (x = 0; x < lineOffset; ++x) {
col = lineBuf[0][lineBufIndex];
retBuf[(lineOffset * y) + x] = col;
++x;
retBuf[(lineOffset * y) + x] = col;
++x;
retBuf[(lineOffset * y) + x] = col;
++lineBufIndex;
}
}
} else {
fprintf (stderr, "Error: the number of color channels is %d.This program only handles 1 or 3\n", bytesPerPix);
return NULL;
}
jpeg_finish_decompress (&cinfo);
jpeg_destroy_decompress (&cinfo);
fclose (inFile);
return retBuf;
}
Makefile
OBJ= showjpeg.o jpeg.o
TARGET=showjpeg
all: $(TARGET)
$(TARGET): $(OBJ)
$(CC) $(OBJ) libjpeg.a -o $(TARGET)
.c.o:
$(CC) -c -o $@ $<
clean:
rm $(TARGET) -f
rm *.o -f
rm *~ -f
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