一、开发环境介绍

开发板：友善之臂Tiny4412

LCD型号: S702 、分辨率: 800*480

Linux内核版本: Linux 3.5

摄像头: USB免驱摄像头

文本显示采用矢量字库, FreeType引擎。

二、核心代码

注意:　文本编码必须是UTF-8编码．

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <poll.h>
#include <string.h>
#include <linux/fb.h>
#include <stdlib.h>
#include <math.h>
#include <wchar.h>
#include <time.h>
#include <string.h>

#include <locale.h>
#include <ft2build.h>
#include FT_FREETYPE_H
#include FT_STROKER_H


struct FREE_TYPE_CONFIG
{
	FT_Library    library;
	FT_Face       face;
	FT_GlyphSlot  slot;
	FT_Vector     pen;                    
	FT_Error      error;
	FT_BBox  bbox;
	FT_Glyph  glyph;
};
struct FREE_TYPE_CONFIG FreeTypeConfig;

typedef unsigned int u32;
typedef unsigned short u16;
typedef unsigned char u8;



int lcd_fd;
unsigned char *lcd_mem_p=NULL;  //保存LCD屏映射到进程空间的首地址
struct fb_var_screeninfo vinfo;
struct fb_fix_screeninfo finfo;
int video_fd;
char *video_buff_buff[4]; 
int video_height=0;
int video_width=0;
unsigned char *lcd_display_buff; //LCD显存空间


void LCD_WritePoint(int x,int y,int c);
int LCD_ReadPoint(int x,int y);



void LCD_DrawBitmap(FT_Bitmap* bitmap,FT_Int x,FT_Int y)
{
  	FT_Int i,j,p,q;
  	FT_Int x_max=x+bitmap->width;
  	FT_Int y_max=y+bitmap->rows;

	
	for(i=x,p=0;i<x_max;i++,p++)
	{
		for(j=y,q=0;j<y_max;j++,q++)
		{
			if((i>x_max)||(j>y_max)||(i<0)||(j<0))continue;
			if(bitmap->buffer[q*bitmap->width+p]!=0)
			{
				LCD_WritePoint(i, j,0xFF0033);
			}
			else
			{
				//LCD_WritePoint(i, j,0xFFFFFF);
			}
		}
	}
}


int InitConfig_FreeType(char *font_file)
{
	FT_Error      error;
	
	error=FT_Init_FreeType(&FreeTypeConfig.library);
	if(error)
	{
		printf("freetype字体库初始化失败.\n");
		return -1;
	}

	
 	error=FT_New_Face(FreeTypeConfig.library,font_file,0,&FreeTypeConfig.face);
  	if(error)
  	{
		printf("矢量字体文件加载失败.\n");
		return -2;
	}
	return 0;
}


void FreeType_Config(void)
{
	FT_Done_Face(FreeTypeConfig.face);
  	FT_Done_FreeType(FreeTypeConfig.library);
}


int LCD_DrawText(u32 x,u32 y,u32 size,wchar_t *text)
{
	FT_Error      error;
	int i = 0;
	int bbox_height_min = 10000;
	int bbox_height_max = 0;
		
	
	error=FT_Set_Pixel_Sizes(FreeTypeConfig.face,size,0);
	if(error)
	{
		printf("字符的像素大小设置失败.\n");
		return -1;
	}
	
	
	FreeTypeConfig.slot=FreeTypeConfig.face->glyph;

	
	FreeTypeConfig.pen.x=x*64;
  	FreeTypeConfig.pen.y=(vinfo.yres-size-y)*64;

	
	for(i=0;i<wcslen(text);i++)
	{
		FT_Set_Transform(FreeTypeConfig.face,0,&FreeTypeConfig.pen);	//设置字体的起始坐标位置
		
		error=FT_Load_Char(FreeTypeConfig.face,text[i],FT_LOAD_RENDER);
		if(error)
		{
			printf("装载字符编码失败.\n");
			return -1;
		}
		
		
		FT_Get_Glyph(FreeTypeConfig.slot,&FreeTypeConfig.glyph);

		
		FT_Glyph_Get_CBox(FreeTypeConfig.glyph,FT_GLYPH_BBOX_TRUNCATE,&FreeTypeConfig.bbox);

		
		if(bbox_height_min>FreeTypeConfig.bbox.yMin)bbox_height_min=FreeTypeConfig.bbox.yMin;
		if(bbox_height_max<FreeTypeConfig.bbox.yMax)bbox_height_max=FreeTypeConfig.bbox.yMax;
		
		
		LCD_DrawBitmap(&FreeTypeConfig.slot->bitmap,
						FreeTypeConfig.slot->bitmap_left,
						vinfo.yres-FreeTypeConfig.slot->bitmap_top);

		if(FreeTypeConfig.slot->bitmap_left+size*2>vinfo.xres)
		{
			FreeTypeConfig.pen.x=0; //更新X坐标位置
			FreeTypeConfig.pen.y=(vinfo.yres-size-y-size)*64; //更新Y坐标位置
		}
		else
		{
			
			FreeTypeConfig.pen.x+=FreeTypeConfig.slot->advance.x;
			FreeTypeConfig.pen.y+=FreeTypeConfig.slot->advance.y;
		}
	}
	return 0;
}

// 将char类型转化为wchar
// src:  源
// dest: 目标
// locale: 环境变量的值，mbstowcs依赖此值来判断src的编码方式
void CharToWchar(char *src, wchar_t *dest)
{
  // 根据环境变量设置locale
  setlocale(LC_CTYPE,"zh_CN.utf8");
  // mbstowcs函数得到转化为需要的宽字符大小: 计算char转为wcchar存放时实际占用空间大小.
  // 也可以直接传入一个大数组代替
  //w_size=mbstowcs(NULL, src, 0) + 1;
  mbstowcs(dest, src, strlen(src)+1);
}


void LCD_WritePoint(int x,int y,int c)
{
    unsigned int *p=(unsigned int *)(lcd_display_buff+vinfo.xres*y*vinfo.bits_per_pixel/8+x*vinfo.bits_per_pixel/8);
    *p=c;
}


int LCD_ReadPoint(int x,int y)
{
    int c;
    unsigned int *p=(unsigned int *)(lcd_display_buff+vinfo.xres*y*vinfo.bits_per_pixel/8+x*vinfo.bits_per_pixel/8);
    c=*p;
    return c;
}


int VideoDev_Init(const char *dev_path)
{
	
	video_fd=open(dev_path,2);
	if(video_fd<0)return -1;
	
	struct v4l2_format video_format;
	memset(&video_format,0,sizeof(struct v4l2_format));
	video_format.type=V4L2_BUF_TYPE_VIDEO_CAPTURE; //捕获设备
	video_format.fmt.pix.height=480;
	video_format.fmt.pix.width=800;
	video_format.fmt.pix.pixelformat=V4L2_PIX_FMT_YUYV;
	if(ioctl(video_fd,VIDIOC_S_FMT,&video_format))return -2;
	printf("当前摄像头支持的分辨率:%dx%d\n",video_format.fmt.pix.width,video_format.fmt.pix.height);
	if(video_format.fmt.pix.pixelformat!=V4L2_PIX_FMT_YUYV)
	{
		printf("当前摄像头不支持YUYV格式输出.\n");
		return -3;
	}
	else
	{
		video_height=video_format.fmt.pix.height;
		video_width=video_format.fmt.pix.width;	
		printf("当前摄像头支持YUYV格式输出.\n");
	}
	
	struct v4l2_requestbuffers video_requestbuffers;
	memset(&video_requestbuffers,0,sizeof(struct v4l2_requestbuffers));
	video_requestbuffers.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
	video_requestbuffers.count=4;
	video_requestbuffers.memory=V4L2_MEMORY_MMAP;
	if(ioctl(video_fd,VIDIOC_REQBUFS,&video_requestbuffers))return -4;
	printf("成功申请的缓冲区数量:%d\n",video_requestbuffers.count);
	
	struct v4l2_buffer video_buffer;
	memset(&video_buffer,0,sizeof(struct v4l2_buffer));
	int i;
	for(i=0;i<video_requestbuffers.count;i++)
	{
		video_buffer.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
		video_buffer.index=i;
		video_buffer.memory=V4L2_MEMORY_MMAP;
		if(ioctl(video_fd,VIDIOC_QUERYBUF,&video_buffer))return -5;
		
		video_buff_buff[i]=mmap(NULL,video_buffer.length,PROT_READ|PROT_WRITE,MAP_SHARED,video_fd,video_buffer.m.offset);
		printf("第%d个缓冲区地址:%#X\n",i,video_buff_buff[i]);
	}	
	
	memset(&video_buffer,0,sizeof(struct v4l2_buffer));
	for(i=0;i<video_requestbuffers.count;i++)
	{
		video_buffer.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
		video_buffer.index=i;
		video_buffer.memory=V4L2_MEMORY_MMAP;
		if(ioctl(video_fd,VIDIOC_QBUF,&video_buffer))return -6;
	}
	
	int opt_type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
	if(ioctl(video_fd,VIDIOC_STREAMON,&opt_type))return -7;
	return 0;
}


void yuv_to_rgb(unsigned char *yuv_buffer,unsigned char *rgb_buffer,int iWidth,int iHeight)
{
	int x;
	int z=0;
	unsigned char *ptr = rgb_buffer;
	unsigned char *yuyv= yuv_buffer;
	for (x = 0; x < iWidth*iHeight; x++)
	{
		int r, g, b;
		int y, u, v;
		if (!z)
		y = yuyv[0] << 8;
		else
		y = yuyv[2] << 8;
		u = yuyv[1] - 128;
		v = yuyv[3] - 128;
		r = (y + (359 * v)) >> 8;
		g = (y - (88 * u) - (183 * v)) >> 8;
		b = (y + (454 * u)) >> 8;
		*(ptr++) = (b > 255) ? 255 : ((b < 0) ? 0 : b);
		*(ptr++) = (g > 255) ? 255 : ((g < 0) ? 0 : g);
		*(ptr++) = (r > 255) ? 255 : ((r < 0) ? 0 : r);
		if(z++)
		{
			z = 0;
			yuyv += 4;
		}
	}
}


int LCD_Init(const char *dev_path)
{
	
    lcd_fd=open(dev_path,2);
    if(lcd_fd<0)
    {
        return -1;
    }
    
    if(ioctl(lcd_fd,FBIOGET_VSCREENINFO,&vinfo))return -2;
    printf("屏幕X:%d   屏幕Y:%d  像素位数:%d\n",vinfo.xres,vinfo.yres,vinfo.bits_per_pixel);
	//分配显存空间,完成图像显示
	lcd_display_buff=malloc(vinfo.xres*vinfo.yres*vinfo.bits_per_pixel/8);
    
    if(ioctl(lcd_fd,FBIOGET_FSCREENINFO,&finfo))return -3;
    printf("smem_len=%d Byte,line_length=%d Byte\n",finfo.smem_len,finfo.line_length);
    
    
    lcd_mem_p =(unsigned char *)mmap(0,finfo.smem_len,PROT_READ|PROT_WRITE,MAP_SHARED,lcd_fd,0); //从文件的那个地方开始映射
    memset(lcd_mem_p,0xFFFFFFFF,finfo.smem_len);
	return 0;
}

//[root@wbyq code]# ./app /dev/video15 simhei.ttf 
//[root@wbyq code]# date -s "2020-09-19 09:39:20"
//编译程序记得加上-lfreetype
int main(int argc,char **argv)
{
	if(argc!=3)
	{
		printf("传参格式:./app </dev/videoX> <矢量字体文件>\n");
		return 0;
	}
	
	InitConfig_FreeType(argv[2]);
	
	
	printf("摄像头初始化状态:%d\n",VideoDev_Init(argv[1]));
	
	printf("LCD显示屏的初始化状态:%d\n",LCD_Init("/dev/fb0"));
	
	struct pollfd video_fds;
	video_fds.events=POLLIN;
	video_fds.fd=video_fd;
	struct v4l2_buffer video_buffer;
	memset(&video_buffer,0,sizeof(struct v4l2_buffer));
	unsigned char *rgb_buffer=malloc(video_height*video_width*3);
	unsigned char *rgb_p;
	int w,h;
	int x0;
	unsigned char r,g,b; 
	unsigned int c;
	time_t sec;
	struct tm c_timedate;
	char time_date[50];
	wchar_t time_date_wchar[100];
	x0=(vinfo.xres-video_width)/2; //摄像头图片显示的起始位置
	while(1)
	{
		
		poll(&video_fds,1,-1);
		
		video_buffer.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
		video_buffer.memory=V4L2_MEMORY_MMAP;
		ioctl(video_fd,VIDIOC_DQBUF,&video_buffer);
		//printf("当前采集OK的缓冲区编号:%d,地址:%#X\n",video_buffer.index,video_buff_buff[video_buffer.index]);
		
		yuv_to_rgb(video_buff_buff[video_buffer.index],rgb_buffer,video_width,video_height);
		
		rgb_p=rgb_buffer;
		for(h=0;h<video_height;h++)
		{
			for(w=0;w<video_width;w++)
			{
				b=*rgb_p++;
				g=*rgb_p++;
				r=*rgb_p++;
				c=r<<16|g<<8|b<<0;
				LCD_WritePoint(w+x0,h,c); 
			}
		}
		
		
		sec=time(NULL); //获取当前系统的秒单位时间
		localtime_r(&sec,&c_timedate); //将秒单位时间转为结构体返回
		
		sprintf(time_date,"%d-%d-%d %d:%d:%d",c_timedate.tm_year+1900,c_timedate.tm_mon+1,c_timedate.tm_mday,c_timedate.tm_hour,c_timedate.tm_min,c_timedate.tm_sec);
		
		//printf("time_date=%s\n",time_date);

		//char类型转Wchar
		CharToWchar(time_date,time_date_wchar);
		LCD_DrawText(x0,0,32,L"实训楼六楼");
		LCD_DrawText(x0,32,32,time_date_wchar);
		
		//显示屏进行显示: 将显存空间的数据拷贝到LCD屏进行显示
		memcpy(lcd_mem_p,lcd_display_buff,vinfo.xres*vinfo.yres*vinfo.bits_per_pixel/8);

		
		ioctl(video_fd,VIDIOC_QBUF,&video_buffer);
	}
	
	close(video_fd);
	return 0;
}

三、编译与运行效果

[root@wbyq code]# ./app /dev/video15 simhei.ttf 
当前摄像头支持的分辨率:640x480
当前摄像头支持YUYV格式输出.
成功申请的缓冲区数量:4
第0个缓冲区地址:0xB6CE9000
第1个缓冲区地址:0xB6C53000
第2个缓冲区地址:0xB6BBD000
第3个缓冲区地址:0xB6B27000
摄像头初始化状态:0
屏幕X:800   屏幕Y:480  像素位数:32
smem_len=4608000 Byte,line_length=3200 Byte
LCD显示屏的初始化状态:0

下面公众号有全套的单片机、QT、C++、C语言、物联网相关的教程，欢迎关注：