linux下直接写framebuffer(fb0)的方式显示bmp图像
linux下的显示设备就是/dev/fb0，往该设备写入的数据会显示在屏幕上，所以我们可以通过直接写frame buffer这个/dev/fb0设备来实现bmp图像的显示，而不用管是在shell文本方式下还是在其他gnome、qt、gtk、wayland等图形模式下，都能显示出来。当前前提是你的linux下必须具有该设备并支持读写（无特殊处理的linux都有该设备）。
代码（支持16位、24位或32位颜色深度的bmp图像，支持24或32位颜色深度的fb0设备）：
#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 <errno.h>
//14byte文件头
typedef struct
{
charcfType[2];//文件类型，”BM”(0x4D42)
int cfSize;//文件大小（字节）
int cfReserved;//保留，值为0
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
{
charciSize[4];//BITMAPFILEHEADER所占的字节数
int ciWidth;//宽度
int ciHeight;//高度
charciPlanes[2];//目标设备的位平面数，值为1
int ciBitCount;//每个像素的位数
charciCompress[4];//压缩说明
charciSizeImage[4];//用字节表示的图像大小，该数据必须是4的倍数
charciXPelsPerMeter[4];//目标设备的水平像素数/米
charciYPelsPerMeter[4];//目标设备的垂直像素数/米
charciClrUsed[4]; //位图使用调色板的颜色数
charciClrImportant[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;
static void FbUpdate(int fbfd, struct fb_var_screeninfo *vi) //将要渲染的图形缓冲区的内容绘制到设备显示屏来
{
vi->yoffset=0; //from 0 to yres will be display.
ioctl(fbfd, FBIOPUT_VSCREENINFO, vi);
}
static int CursorBitmapFormatConvert(char *dst, char *src, int screenXres, int screenYres, int bytes_per_pixel_screen,
intbmpWidth, intbmpHeight, intbytes_per_pixel_bitmap)
{
int i ,j ;
char*psrc = src ;
char*pdst = dst;
char*p = psrc;
int oldi =0;
int left_right = (screenXres-bmpWidth)/2;
int top_bottom = (screenYres-bmpHeight)/2;
printf(“left_right: %d, top_bottom: %d\n”, left_right, top_bottom);
printf(“screenXres: %d, screenYres: %d\n”, screenXres, screenYres);
printf(“bmpWidth: %d, bmpHeight: %d\n”, bmpWidth, bmpHeight);
if(left_right <0&& top_bottom <0){
printf(“error: BMP is too big, screen X: %d, Y: %d, bmp width: %d, height: %d\n”, screenXres, screenYres, bmpWidth, bmpHeight);
return-1;
}
/* 由于bmp存储是从后面往前面，所以需要倒序进行转换 */
pdst += (screenXres * bmpHeight * bytes_per_pixel_screen);
pdst += (screenXres * top_bottom * bytes_per_pixel_screen); //move to middle bmpHeight
for(i=0; i<bmpHeight; i++){
p = psrc + (i+1) * bmpWidth * bytes_per_pixel_bitmap;
if(i ==0)
pdst -= (left_right * bytes_per_pixel_screen); //move to middle bmpWidth
else
pdst -= (left_right * 2 * bytes_per_pixel_screen); //move to middle bmpWidth
for(j=0; j<bmpWidth; j++){
pdst -= bytes_per_pixel_screen;
p -= bytes_per_pixel_bitmap;
int kk =0;
int k;
for(k=0; k<bytes_per_pixel_screen; k++){
if(kk >= bytes_per_pixel_bitmap)
pdst[k] =255; // 3: alpha color
else
pdst[k] =p[kk]; // 0: blue, 1: green, 2: red
kk++;
}
}
}
pdst -= (left_right * bytes_per_pixel_screen); // move to 0 position
return0;
}
int ShowBmp(char *path, int fbfd, struct fb_var_screeninfo *vinfo, char *fbp)
{
int i;
FILE *fp;
int rc;
int line_x, line_y;
longint location =0, BytesPerLine =0;
char*bmp_buf =NULL;
char* buf =NULL;
int flen =0;
int ret =-1;
int total_length =0;
BITMAPFILEHEADER FileHead;
BITMAPINFOHEADER InfoHead;
int width, height;
printf(“into ShowBmp function\n”);
if(path ==NULL) {
printf(“path Error,return\n”);
return-1;
}
printf(“path = %s\n”, path);
fp = fopen( path, “rb” );
if(fp ==NULL){
printf(“load cursor file open failed\n”);
return-1;
}
/* 求解文件长度 */
fseek(fp,0,SEEK_SET);
fseek(fp,0,SEEK_END);
flen = ftell(fp);
printf(“flen is %d\n”,flen);
bmp_buf = (char*)calloc(1,flen – 54);
if(bmp_buf ==NULL){
printf(“load > malloc bmp out of memory!\n”);
return-1;
}
/* 再移位到文件头部 */
fseek(fp,0,SEEK_SET);
rc = fread(&FileHead, sizeof(BITMAPFILEHEADER),1, fp);
if ( rc !=1) {
printf(“read header error!\n”);
fclose( fp );
return( -2 );
}
//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 );
}
rc = fread( (char *)&InfoHead, sizeof(BITMAPINFOHEADER),1, fp );
if ( rc !=1) {
printf(“read infoheader error!\n”);
fclose( fp );
return( -4 );
}
width = InfoHead.ciWidth;
height = InfoHead.ciHeight;
printf(“FileHead.cfSize =%d byte\n”,FileHead.cfSize);
printf(“flen = %d\n”, flen);
printf(“width = %d, height = %d\n”, width, height);
//跳转的数据区
fseek(fp, FileHead.cfoffBits, SEEK_SET);
printf(” FileHead.cfoffBits = %d\n”, FileHead.cfoffBits);
printf(” InfoHead.ciBitCount = %d\n”, InfoHead.ciBitCount);
int bytes_per_pixel_bitmap =InfoHead.ciBitCount/8;
total_length = width * height * bytes_per_pixel_bitmap;
printf(“total_length = %d\n”, total_length);
//每行字节数
buf = bmp_buf;
while ((ret =fread(buf,1,total_length,fp)) >=0) {
if (ret ==0) {
usleep(100);
continue;
}
printf(“ret = %d\n”, ret);
buf = ((char*) buf) + ret;
total_length = total_length – ret;
if(total_length ==0)
break;
}
CursorBitmapFormatConvert(fbp, bmp_buf, (*vinfo).xres, (*vinfo).yres, (*vinfo).bits_per_pixel/8, width, height, bytes_per_pixel_bitmap);
free(bmp_buf);
fclose(fp);
printf(“show logo return 0\n”);
return0;
}
int ShowPicture(int fbfd, char *path)
{
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
longint screensize =0;
struct fb_bitfield red;
struct fb_bitfield green;
struct fb_bitfield blue;
//打开显示设备
printf(“fbfd = %d\n”, fbfd);
if (fbfd ==-1) {
//printf(“Error opening frame buffer errno=%d (%s)\n”,errno, strerror(errno));
return-1;
}
if (ioctl(fbfd, FBIOGET_FSCREENINFO, &finfo)) {
//printf(“Error：reading fixed information.\n”);
return-1;
}
if (ioctl(fbfd, FBIOGET_VSCREENINFO, &vinfo)) {
//printf(“Error: reading variable information.\n”);
return-1;
}
//printf(“R:%x ;G:%d ;B:%d \n”, (int)vinfo.red, vinfo.green, vinfo.blue );
printf(“%dx%d, %dbpp\n”, vinfo.xres, vinfo.yres, 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=%ld byte\n”,screensize);
//对象映射
char*fbp = (char*)mmap(0, screensize, PROT_READ | PROT_WRITE, MAP_SHARED, fbfd, 0);
if (fbp == (char*)-1) {
printf(“Error: failed to map framebuffer device to memory.\n”);
return-1;
}
printf(“sizeof file header=%ld\n”, sizeof(BITMAPFILEHEADER));
//显示图像
ShowBmp(path, fbfd, &vinfo, fbp);
FbUpdate(fbfd, &vinfo);
///在屏幕上显示多久
sleep(10);
//删除对象映射
munmap(fbp, screensize);
return0;
}
int main()
{
int fbfd =0;
fbfd = open(“/dev/fb0”, O_RDWR);
if (!fbfd) {
printf(“Error: cannot open framebuffer device.\n”);
return-1;
}
ShowPicture(fbfd, “/tmp/license_ckx.bmp”);
close(fbfd);
return0;
}