继前面的文章，本文是一个测试例子，并给出测试结果。
将图片转换成目标文件命令与x86平台相类似，只需修改几个参数即可。 命令如下：
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| $ arm-linux-objcopy -I binary -O elf32-littlearm -B arm logo.jpg logo.o
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需要注意的是输出文件的格式，即-O选项的内容，这里是elf32-littlearm，原来是写elf32-little，但转换得到的目标文件没有机器类型，即便用-B arm指定也不行。
下面是完整的源文件：
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| /****************************************************************
$ arm-linux-objcopy -I binary -O elf32-littlearm -B arm logo.jpg logo.o
$ arm-linux-gcc jpeg_test.c fb_utils.c -o jpeg_test -I/your/jpeg/.h
-L/your/jpeg/lib -ljpeg
$ arm-linux-gcc jpeg_test.c fb_utils.c logo.o
-I/home/latelee/my2440/lib_pic/include -L/home/latelee/my2440/lib_pic/lib
-ljpeg -o jpeg_test
*****************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <jpeglib.h>
#include <jerror.h>
#include "fb_utils.h"
static int fb_width;
static int fb_height;
static int fb_depth;
static unsigned char *fb_mem;
// test of pic
extern _binary_logo_jpg_start;
extern _binary_logo_jpg_end;
extern _binary_logo_jpg_size;
/**
* jpeg_init - init jpeg width height, etc.
*
* note:
* Must call fb_init() before this function.
*/
int jpeg_init(void)
{
if (fb) {
fb_width = fb->width;
fb_height = fb->height;
fb_depth = fb->bytes_per_pixel*8;
fb_mem = fb->fbmem;
return 0;
} else {
// printf("init fb first\n");
return -1;
}
}
/**
* draw_jpeg - Display a jpeg picture from (0, 0) on framebuffer
* @name: picture name(foo.jpg)
*/
int draw_jpeg()
{
struct jpeg_decompress_struct cinfo;
struct jpeg_error_mgr jerr;
unsigned char *jpeg_buf;
unsigned long size;
unsigned char *buffer;
int x, y;
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_decompress(&cinfo);
// come from logo.o, see detail with $ arm-linux-objdump -ht logo.o
jpeg_buf = (unsigned char *)&_binary_logo_jpg_start;
size = (unsigned long)&_binary_logo_jpg_size;
// memory
jpeg_mem_src(&cinfo, jpeg_buf, size);
jpeg_read_header(&cinfo, TRUE);
jpeg_start_decompress(&cinfo);
if ((cinfo.output_width > fb_width) || (cinfo.output_height > fb_height)) {
printf("too large JPEG file,cannot display\n");
return -1;
}
buffer = (unsigned char *) malloc(cinfo.output_width * cinfo.output_components);
//printf("%d %d\n", cinfo.output_width, cinfo.output_components); /*eg, 240 3(rgb888)*/
x = y = 0;
while (cinfo.output_scanline < cinfo.output_height) {
jpeg_read_scanlines(&cinfo, &buffer, 1);
if (fb_depth == 16) {
unsigned short color;
for (x=0; x < cinfo.output_width; x++) {
color = make16color(buffer[x*3], buffer[x*3+1], buffer[x*3+2]);
// the pic frome (45, 200)
fb_pixel(x + 45, y + 200, color);
}
} else if (fb_depth == 24) {
// not test
memcpy((unsigned char *) fb_mem + y * fb_width * 3,
buffer, cinfo.output_width * cinfo.output_components);
}
y++; // next scanline
}
jpeg_finish_decompress(&cinfo);
jpeg_destroy_decompress(&cinfo);
free(buffer);
return 0;
}
int main(int argc, char *argv[])
{
fb_init(); // must call first
jpeg_init();
draw_jpeg();
fb_release();
return 0;
}
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说明几点：
1、程序没有显式指定_binary_logo_jpg_start这几个符号的类型，编译器默认是int，如果用-Wall，会得到
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| warning: type defaults to 'int' in declaration of '_binary_logo_jpg_start'
|
的警告，如果要去掉警告，就将它们几个声明为int。
2、程序使用jpeg_mem_src函数指定图片在内存的位置及大小，两者从&_binary_logo_jpg_start和&_binary_logo_jpg_size得到。为了去除编译器的警告，进行了类型转换。
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2
| jpeg_buf = (unsigned char *)&_binary_logo_jpg_start;
size = (unsigned long)&_binary_logo_jpg_size;
|
3、由于这个程序将会与其它程序合并，因此将图片放到合适的位置，代码：
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| fb_pixel(x + 45, y + 200, color);
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即图片起点在(45, 200)处。
效果图如下：
更正：原文后面的“合同”为笔误，已更正为“合并”，发表后约三天发现。
