提取bmp图片的颜色信息，可直接framebuffer显示

Posted 2020-08-20 QB杂货铺

稍微了解了下linux的framebuffer，这是一种很简单的显示接口，直接写入像素信息即可

配置好的内核，会有/dev/fbn 的接口，于是想能否提前生成一个文件，比如logo.fb，里面仅包含像素信息，从而可以直接送入framebuffer显示

搜索了一下，有不少文章介绍，如何解析bmp图片并送给framebuffer显示，但没有找到预处理工具，都是直接处理完就送入framebuffer

于是参考了一篇文章，改动了下代码，将直接送入framebuffer变成写到一个文件中。

原代码地址为

http://blog.csdn.net/xsckernel/article/details/49992315

测试得到的文件，是可以直接  cat logo.fb > /dev/fb0 进行显示的

#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>

//author：http://blog.csdn.net/xsckernel/article/details/49992315
//modify :zqb-all


//14byte文件头
typedef struct
{
    char    cfType[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
{
    char ciSize[4];//BITMAPFILEHEADER所占的字节数
    int  ciWidth;//宽度
    int  ciHeight;//高度
    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 char blue;
    unsigned char green;
    unsigned char red;
    unsigned char reserved;
}__attribute__((packed)) PIXEL;//颜色模式RGB

BITMAPFILEHEADER FileHead;
BITMAPINFOHEADER InfoHead;

static char *fbp = 0;
static int xres = 0;
static int yres = 0;
static int bits_per_pixel = 0;
int width, height;

int show_bmp();
int fbfd = 0;


static int cursor_bitmap_format_convert(char *dst,char *src)
{
    int i ,j ;
    char *psrc = src ;
    char *pdst = dst;
    char *p = psrc;

    /* 由于bmp存储是从后面往前面，所以需要倒序进行转换 */
    pdst += (width * height * 3);
    for(i=0;i<height;i++){
        p = psrc + (i+1) * width * 3;
        for(j=0;j<width;j++){
            pdst -= 3;
            p -= 3;
            pdst[0] = p[0];
            pdst[1] = p[1];
            pdst[2] = p[2];
        }
    }
    return 0;
}

int show_bmp(char *path,char *fb_path)
{
    int i;
    FILE *fp,*fb_file;
    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 || fb_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;
    }

    printf("fb_path = %s\n", fb_path);
    fb_file = fopen( fb_path, "wb" );
    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);

    total_length = width * height *3;

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

    //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);

    //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;
    }

    ///重新计算，很重要！！
    total_length = width * height *3;
    bmp_buf_dst = (char*)calloc(1,total_length );
    if(bmp_buf_dst == NULL){
        printf("load > malloc bmp out of memory!\n");
        return -1;
    }

    cursor_bitmap_format_convert(bmp_buf_dst, bmp_buf);
    fwrite(bmp_buf_dst,1,total_length,fb_file);
    free(bmp_buf);
    free(bmp_buf_dst);

    fclose(fp);
    fclose(fb_file);

    printf("show logo return 0\n");
    return 0;
}


int main()
{

    show_bmp( "./logo.bmp","./logo.fb");

}