通过写framebuffer显示BMP图片

 

#include
#include
#include
#include
#include
#include
#include
#include
#include


//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 );
}