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关键：
1)字节对齐问题__attribute__((packed)) 最大字节对齐
2)_attribute__((packed))的作用是告诉编译器取消结构在编译过程中的优化对齐
3) 字节数的统计
#include
#include
#include
#include
#include
#include /*map头文件*/
#include
#include
#include
#include
//14byte文件头
typedef struct
{
unsigned char cfType[2];//文件类型，"BM"(0x4D42)
unsigned int cfSize;//文件大小(字节)
unsigned int cfReserved;//保留，值为0
unsigned int cfoffBits;//数据区相对于文件头的偏移量(字节)
}__attribute__((packed)) BITMAPFILEHEADER;
/*_attribute__((packed))的作用是告诉编译器取消结构在
编译过程中的优化对齐 */
//40byte信息头
typedef struct
{
unsigned int ciSize;//BITMAPFILEHEADER所占的字节数
unsigned int ciWidth;//宽度
unsigned int ciHeight;//高度
unsigned short int ciPlanes;//目标设备的位平面数，值为1
unsigned short int ciBitCount;//每个像素的位数
char ciCompress[4];//压缩说明
unsigned int ciSizeImage;//用字节表示的图像大小，该数据必须是4的倍数
unsigned int ciXPelsPerMeter;//目标设备的水平像素数/米
unsigned int ciYPelsPerMeter;//目标设备的垂直像素数/米
unsigned int ciClrUsed; //位图使用调色板的颜色数
unsigned intciClrImportant; //指定重要的颜色数，当该域的值等于颜色数时(或者等于0时)，表示所有颜色都一样重要
}__attribute__((packed)) BITMAPINFOHEADER;
typedef struct
{
unsigned char blue;
unsigned char green;
unsigned char red;
}__attribute__((packed)) PIXEL;//颜色模式RGB
BITMAPFILEHEADER FileHead;
BITMAPINFOHEADER InfoHead;
static int xres = 0;
static int yres = 0;
static int bits_per_pixel = 0;
static char *fb_addr = NULL;
int show_bmp(char *picname)
{
FILE *fp;
int rc;
int line_x, line_y;
long int location = 0;
char tmp[1024*10];
static unsigned short b,g,r;
static unsigned short rgb; /*2个字节*/
PIXEL pix;
fp = fopen( picname, "rb" );
if (fp == NULL)
{
printf("open errror\n");
return( -1 );
}
printf("Open OK \n");
/* BITMAPFILEHEADER*/
rc = fread( &FileHead, sizeof(BITMAPFILEHEADER),1, fp );
if ( rc != 1)
{
printf("read header error!\n");
fclose( fp );
return( -2 );
}
printf("Read BITMAPFILEHEADER OK\n");
//检测是否是bmp图像
if (memcmp(FileHead.cfType, "BM", 2) != 0)
{
printf("it's not a BMP file\n");
fclose( fp );
return( -3 );
}
/*BITMAPINFOHEADER*/
rc = fread( (char *)&InfoHead, sizeof(BITMAPINFOHEADER),1, fp );
if ( rc != 1)
{
printf("read infoheader error!\n");
fclose( fp );
return( -4 );
}
printf("Read BITMAPINFOHEADER OK\n");
//跳转的数据区
fseek(fp, FileHead.cfoffBits, SEEK_SET);
//向framebuffer中写BMP图片 rgb高位有效
for (line_y = 0; line_y
for (line_x = 0; line_x
{
rc = fread(&pix , sizeof(PIXEL),1, fp);
location = line_x*2+(yres-line_y)*xres*2;
r=((pix.red>>3)<<11)&0xfb80;
g=((pix.green>>2)<<5)&0x07e0;
b=(pix.blue>>3)&0x001f;
rgb=r|g|b;
*((unsigned short *)(fb_addr+location)) = rgb;
}
fclose( fp );
return 0 ;
}
int main(int argc, char *argv[ ])
{
int fbfd,fb_size ;
struct fb_var_screeninfo vinfo; /*记录用户可修改的显示控制参数*/
struct fb_fix_screeninfo finfo; /*取得缓冲区的物理地址*/
// 打开/dev/fb*设备文件
fbfd = open("/dev/fb0", O_RDWR|O_CREAT, S_IRWXU);
if (fbfd <0 )
{
printf("open error\n");
exit(1);
}
//需要的 屏幕内存空间的字节数,取得显示屏幕参数
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo))
{
printf("Error reading variable information.\n");
exit(1);
}
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))
{
printf("Error reading variable information.\n");
exit(1);
}
printf("R:%d,G:%d,B:%d \n", vinfo.red, vinfo.green, vinfo.blue );
printf("%dx%d, %dbpp\n", vinfo.xres, vinfo.yres, vinfo.bits_per_pixel );
xres=vinfo.xres; /*可见解析度*/
yres=vinfo.yres;
bits_per_pixel=vinfo.bits_per_pixel; /* 每像素位数*/
fb_size=xres*yres*bits_per_pixel/8; /*计算屏幕的总大小(字节)*/
// fd的内存地址空间映射到我们的程序地址空间
// void *mmap(void *start, size_t length, int prot, int flags,int fd, off_t offset);
if ( (fb_addr = (char *)mmap( 0, fb_size, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0) )<0)
{
printf( "mmap error\n" );
exit(1);
}
printf("show_bmp\n");
show_bmp( argv[1] );
//删除对象映射
munmap(fb_addr, fb_size);
close(fbfd);
return 0;
}
执行开发板程序：
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