通过写framebuffer显示BMP图片

#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>

//14byte文件头

typedef struct

{

char cfType[2];//文件类型，"BM"(0x4D42)

long cfSize;//文件大小（字节）

long cfReserved;//保留，值为0

long 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，按照实际占用字节数进行对齐

//40byte信息头

typedef struct

{

char ciSize[4];//BITMAPFILEHEADER所占的字节数

long ciWidth;//

long ciHeight;//

char ciPlanes[2];//目标设备的位平面数，值为1

int ciBitCount;//每个像素的位数

char ciCompress[4];//压缩说明

char ciSizeImage[4];//用字节表示的图像大小，该数据必须是4的倍数

char ciXPelsPerMeter[4];//目标设备的水平像素数/米

char ciYPelsPerMeter[4];//目标设备的垂直像素数/米

char ciClrUsed[4]; //位图使用调色板的颜色数

char ciClrImportant[4]; //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 short red:5;

unsigned short green:6;

unsigned short blue:5;

}__attribute__((packed)) PIXEL;//颜色模式，RGB565

BITMAPFILEHEADER FileHead;

BITMAPINFOHEADER InfoHead;

static char *fbp = 0;

static int xres = 0;

static int yres = 0;

static int bits_per_pixel = 0;

int show_bmp();

int main ( int argc, char *argv[] )

{

int fbfd = 0;

struct fb_var_screeninfo vinfo;

struct fb_fix_screeninfo finfo;

long int screensize = 0;

//打开显示设备

fbfd = open("/dev/graphics/fb0", O_RDWR);

if (!fbfd)

{

printf("Error: cannot open framebuffer device.\n");

exit(1);

}

if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo))

{

printf("Error：reading fixed information.\n");

exit(2);

}

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;

//计算屏幕的总大小（字节）

screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;

printf("screensize=%d\n",screensize);

//内存映射

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);

}

printf("sizeof header=%d\n", sizeof(BITMAPFILEHEADER));

printf("into show_bmp function\n");

show_bmp();

munmap(fbp, screensize);

close(fbfd);

return 0;

}

int show_bmp()

{

FILE *fp;

int rc;

int line_x, line_y;

long int location = 0, BytesPerLine = 0;

char tmp[1024*10];

fp = fopen( "./calibration.bmp", "rb" );

if (fp == NULL)

{

return( -1 );

}

rc = fread( &FileHead, sizeof(BITMAPFILEHEADER),1, fp );

if ( rc != 1)

{

printf("read header error!\n");

fclose( fp );

return( -2 );

}

if (memcmp(FileHead.cfType, "BM", 2) != 0)

{

printf("it's not a BMP file\n");

fclose( fp );

return( -3 );

}

rc = fread( (char *)&InfoHead, sizeof(BITMAPINFOHEADER),1, fp );

if ( rc != 1)

{

printf("read infoheader error!\n");

fclose( fp );

return( -4 );

}

//跳转的数据区

fseek(fp, FileHead.cfoffBits, SEEK_SET);

//每行字节数

BytesPerLine = (InfoHead.ciWidth * InfoHead.ciBitCount + 31) / 32 * 4;

line_x = line_y = 0;

//向framebuffer中写BMP图片

while(!feof(fp))

{

PIXEL pix;

unsigned short int tmp;

rc = fread( (char *)&pix, 1, sizeof(unsigned short int), fp);

if (rc != sizeof(unsigned short int))

{

break;

}

location = line_x * bits_per_pixel / 8 + (InfoHead.ciHeight - line_y - 1) * xres * bits_per_pixel / 8;

//显示每一个像素

tmp=pix.red<<0 | pix.green<<5 | pix.blue<<11;

*((unsigned short int*)(fbp + location)) = tmp;

line_x++;

if (line_x == InfoHead.ciWidth )

{

line_x = 0;

line_y++;

if(line_y == InfoHead.ciHeight)

{

break;

}

}

}

fclose( fp );

return( 0 );

}