0.framebuffer简介
帧缓冲(framebuffer)是Linux为显示设备提供的一个接口,把显存抽象后的一种设备,他允许上层应用程序在图形模式下直接对显示缓冲区进行读写操作。framebuffer是LCD对应的一中HAL(硬件抽象层),提供抽象的,统一的接口操作,用户不必关心硬件层是怎么实施的。这些都是由Framebuffer设备驱动来完成的。
1.图片
下载图片的大小应该和显示屏大小一致
显示屏大小可以通过代码来查看,参考:什么是framebuffer,怎么应用(一)————如何画点、线、矩形、圆
2.代码
参考:Linux framebuffer显示bmp图片
2.1位图文件头
位图文件头(BITMAPFILEHEADER)是BMP位图文件的一个重要组成部分,主要用于识别文件是否为位图文件,并提供文件大小和位图数据的位置等信息。以下是位图文件头的详细结构和说明:
-
结构定义:
- 位图文件头通常占据14个字节,其结构定义如下:
typedef struct tagBITMAPFILEHEADER {WORD bfType; // 2字节,位图文件类型,必须为'BM'(0x4D42)DWORD bfSize; // 4字节,文件大小(以字节为单位)WORD bfReserved1; // 2字节,保留字段,通常为0WORD bfReserved2; // 2字节,保留字段,通常为0DWORD bfOffBits; // 4字节,从文件头到实际位图数据的偏移量(以字节为单位) } BITMAPFILEHEADER;
- 位图文件头通常占据14个字节,其结构定义如下:
-
字段解释:
bfType
:该字段用于标识文件类型,对于BMP文件,这个值必须是’BM’(即0x4D42)。这是识别文件是否为位图文件的关键。bfSize
:该字段表示整个文件的大小,以字节为单位。这有助于确定文件是否已完整下载或传输。bfReserved1
和bfReserved2
:这两个字段是保留字段,通常设置为0。在某些情况下,这些字段可能被用于特定的用途,但在标准的BMP文件中,它们不被使用。bfOffBits
:该字段表示从文件头到实际位图数据的偏移量,以字节为单位。通过这个字段,程序可以快速地定位到位图数据的起始位置。
-
作用:
- 位图文件头的主要作用是标识文件类型,确保程序能够正确地解析文件。同时,它还提供了关于文件大小和位图数据位置的信息,这些信息对于读取和解析位图文件至关重要。
在解析BMP文件时,程序首先会读取文件头,并检查bfType
字段的值是否为’BM’。如果不是,则该文件不是有效的BMP文件。然后,程序会根据bfSize
和bfOffBits
字段的值来读取和解析文件的其余部分。
2.2具体实现
#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>#include <errno.h>typedef struct{char cfType[2];long cfSize;long cfReserved;long cfoffBits;}__attribute__((packed)) BITMAPFILEHEADER;typedef struct{char ciSize[4];long ciWidth;long ciHeight;char ciPlanes[2];int ciBitCount;char ciCompress[4];char ciSizeImage[4];char ciXPelsPerMeter[4];char ciYPelsPerMeter[4];char ciClrUsed[4];char ciClrImportant[4];}__attribute__((packed)) BITMAPINFOHEADER;typedef struct{unsigned short blue;unsigned short green;unsigned short red;unsigned short reserved;}__attribute__((packed)) PIXEL;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 show_bmp2();int fbfd = 0;static void fb_update(struct fb_var_screeninfo *vi){vi->yoffset = 1;ioctl(fbfd, FBIOPUT_VSCREENINFO, vi);vi->yoffset = 0;ioctl(fbfd, FBIOPUT_VSCREENINFO, vi);}int width, height;static int cursor_bitmpa_format_convert(char *dst,char *src){int i ,j ;char *psrc = src ;char *pdst = dst;char *p = psrc;int value = 0x00;pdst += (width * height * 4);for(i=0;i<height;i++){p = psrc + (i+1) * width * 3;for(j=0;j<width;j++){pdst -= 4;p -= 3;pdst[0] = p[0];pdst[1] = p[1];pdst[2] = p[2];value = *((int*)pdst);value = pdst[0];if(value == 0x00){pdst[3] = 0x00;}else{pdst[3] = 0xff;}}}return 0;}int show_bmp(char *path){FILE *fp;int rc;int line_x, line_y;long int location = 0, BytesPerLine = 0;char *bmp_buf = NULL;char *bmp_buf_dst = NULL;char * buf = NULL;int flen = 0;int ret = -1;int total_length = 0;printf("into show_bmp function____________________________\n");if(path == NULL){printf("path Error,return");return -1;}printf("path = %s\n", path);fp = fopen( path, "rb" );if(fp == NULL){printf("load > cursor file open failed");return -1;}fseek(fp,0,SEEK_SET);fseek(fp,0,SEEK_END);flen = ftell(fp);printf("File size: %d\n", flen); // Debug: print file sizebmp_buf = (char*)calloc(1,flen - 54);if(bmp_buf == NULL){printf("load > malloc bmp out of memory!");return -1;}fseek(fp,0,SEEK_SET);rc = fread(&FileHead, sizeof(BITMAPFILEHEADER),1, fp);if ( rc != 1){printf("read header error!\n");fclose( fp );return( -2 );}// Debug: print BMP header fieldsprintf("BMP Header:\n");printf("cfType: %c%c\n", FileHead.cfType[0], FileHead.cfType[1]);printf("cfSize: %ld\n", FileHead.cfSize);printf("cfReserved: %ld\n", FileHead.cfReserved);printf("cfoffBits: %ld\n", FileHead.cfoffBits);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-224;total_length = width * height *3;fseek(fp, FileHead.cfoffBits, SEEK_SET); buf = bmp_buf;while ((ret = fread(buf,1,total_length,fp)) >= 0) {//printf("ret = %d", ret);if (ret == 0) {if (feof(fp)) {printf("End of file reached.\n");break;}if (ferror(fp)) {perror("Error reading file");break;}usleep(100);continue;}printf("ret = %d\n", ret);buf = ((char*) buf) + ret;total_length = total_length - ret;if(total_length == 0)break;}total_length = width * height * 4;printf("total_length = %d\n", total_length);bmp_buf_dst = (char*)calloc(1,total_length);if(bmp_buf_dst == NULL){printf("load > malloc bmp out of memory!");return -1;}cursor_bitmpa_format_convert(bmp_buf_dst, bmp_buf);memcpy(fbp,bmp_buf_dst,total_length);printf("show logo return 0\n");return 0;}int show_picture(int fd, char *path){struct fb_var_screeninfo vinfo;struct fb_fix_screeninfo finfo;long int screensize = 0;struct fb_bitfield red;struct fb_bitfield green;struct fb_bitfield blue;printf("Enter show_logo\n");retry1:fbfd = fd;if (fbfd == -1){printf("Error opening frame buffer errno=%d (%s)",errno, strerror(errno));goto retry1;}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:%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;yres = vinfo.yres;bits_per_pixel = vinfo.bits_per_pixel;screensize = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;printf("screensize=%d byte\n",screensize);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");return -1;}printf("sizeof file header=%d\n", sizeof(BITMAPFILEHEADER));show_bmp(path);sleep(2); // 暂停2秒fb_update(&vinfo);munmap(fbp, screensize);printf("Exit show_logo\n");return 0;}int main(int argc, char *argv[]) {if (argc != 2) {printf("Usage: %s <bmp file path>\n", argv[0]);return -1;}int fd = open("/dev/fb0", O_RDWR);if (fd == -1) {perror("Error opening framebuffer device");return -1;}if (show_picture(fd, argv[1]) == -1) {printf("Failed to display picture\n");close(fd);return -1;}close(fd);return 0;}
如果图片大小不一致,例如我使用的图片为:1280x1024
//这里要对图片的长宽进行校准width = InfoHead.ciWidth;height = InfoHead.ciHeight-224;
3.编译及远程传输
参考本人前文。