【C语言】之获取显存一帧数据并保存为pnm格式图片

悠悠 2022-05-29 01:44 272阅读 0赞

#include <stdio.h>
    #include <unistd.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <sys/ioctl.h>
    #include <sys/mman.h>
    #include <linux/fb.h>
    
    int main(int argc, char **argv)
    { 
    	int fd;
    
    	/* 检查参数 */
    	if (argc != 2)
    	{ 
    		fprintf(stderr, "Usage: ./a.out pnm_file\n");
    		return -1;
    	}
    
    	/* 打开显存设备 */
    	fd = open("/dev/fb0", O_RDWR);
    	if (fd < 0)
    	{ 
    		perror("opne fb0");
    		return -1;
    	}
    
    	/* 获取屏幕信息 */
    	struct fb_fix_screeninfo fix_info;
    	struct fb_var_screeninfo var_info;
    	int ret, x, y;
    	int line_length;
    
    	ret = ioctl(fd, FBIOGET_FSCREENINFO, &fix_info);
    	if (ret < 0)
    	{ 
    		perror("ioctl fix_info");
    		close(fd);
    		return -2;
    	}
    	ret = ioctl(fd, FBIOGET_VSCREENINFO, &var_info);
    	if (ret < 0)
    	{ 
    		perror("ioctl var_info");
    		close(fd);
    		return -3;
    	}
    	line_length = fix_info.line_length;
    	y = var_info.yres; // 屏幕行数
    	x = line_length / (var_info.bits_per_pixel / 8); // 屏幕列数
    
    	/* 内存映射：提高速度 */
    	unsigned char *fb_addr = mmap(NULL, y * line_length, PROT_READ, MAP_SHARED, fd, 0);
    	if (MAP_FAILED == fb_addr)
    	{ 
    		perror("mmap");
    		close(fd);
    		return -4;
    	}
    
    	/* 打开目标文件 */
    	FILE *fl;
    	fl = fopen(argv[1], "w");
    	if (NULL == fl)
    	{ 
    		fprintf(stderr, "open %s failed!\n", argv[1]);
    		munmap(fb_addr, y * line_length);
    		close(fd);
    		return -5;
    	}
    
    	/* 写pnm头 */
    	fprintf(fl, "P6\n%d %d\n255\n", x, y);
    
    	/* * 写rgb数据： * 显存数据存储方式是: B G R A * bmp图片格式为: B G R * 而pnm图片格式是: R G B */
    	int i, j;
    	unsigned char *tmp = fb_addr;
    	for (i = 0; i < y; i++)
    	{ 
    		for (j = 0; j < x; j++)
    		{ 
    			fwrite(&tmp[2], 1, 1, fl); // R
    			fwrite(&tmp[1], 1, 1, fl); // G
    			fwrite(&tmp[0], 1, 1, fl); // B
    			tmp += 4;// A
    		}
    	}
    
    	fclose(fl);
    	close(fd);
    	munmap(fb_addr, y * line_length);
    	return 0;
    }