嵌入式学习（day26）frambuffer帧缓冲

一、UI技术: User interface

（1）framebuffer: 帧缓冲、帧缓存技术
Linux内核专门为图形化显示提供的一套应用程序接口。

流程如下：

1. 打开显示设备 (/dev/fb0)
2. 获取显示设备相关参数（分辨率，像素格式）---》ioctl
3. 建立显存空间和用户空间的内存映射
4. 向映射的用户空间写入RGB颜色值
5. 解除映射关系
6. 关闭显示设备

二、mmap（内存映射）函数使用：将显存映射到用户空间，方便直接读写：

void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);
功能: 建立内存映射
参数:
addr: 映射的用户空间首地址
NULL: 让操作系统自己分配用户空间
length: 要映射的空间大小
prot: 操作权限
PROT_READ Pages may be read.
PROT_WRITE Pages may be written
flag: MAP_SHARED
fd: 显示设备文件描述符
offset: 偏移量
0: 从显存开头映射
返回值:
成功: 映射的用户空间首地址
失败: MAP_FAILED ((void *)-1)

三、练习：

1. 封装函数绘制横线
2. 封装函数绘制竖线
3. 封装函数绘制矩形
4. 封装函数绘制圆
5. 封装函数绘制bmp图片
6. 封装函数绘制文字

framebuffer.c

//framebuffer.c文件：#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <linux/fb.h>
#include <sys/mman.h>
#include "framebuffer.h"
#include <math.h>void *pmem = NULL;
int fb;
struct fb_var_screeninfo vinfo;int init_fb(char *devname)
{//1. 打开显示设备(/dev/fb0)fb = open(devname, O_RDWR);if (-1 == fb){perror("open fb error");return -1;}//2. 获取显示设备相关参数（分辨率，像素格式）int ret = ioctl(fb, FBIOGET_VSCREENINFO, &vinfo);if (ret < 0){perror("ioctl error");return -1;}printf("xres = %d, yres = %d\n", vinfo.xres, vinfo.yres);printf("xres_virtual = %d, yres_virtual = %d\n", vinfo.xres_virtual, vinfo.yres_virtual);printf("bits_per_pixel = %d\n", vinfo.bits_per_pixel);//3. 建立显存空间和用户空间的内存映射size_t len = vinfo.xres_virtual * vinfo.yres_virtual * vinfo.bits_per_pixel/8;pmem = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fb, 0);if (pmem == MAP_FAILED){perror("mmap error");return -1;}return 0;
}int uninit_fb()
{//5. 解除映射关系//6. 关闭显示设备size_t len = vinfo.xres_virtual * vinfo.yres_virtual * vinfo.bits_per_pixel/8;munmap(pmem, len);close(fb);}void draw_point(int x, int y, unsigned int col)
{if (x >= vinfo.xres || y >= vinfo.yres){return ;}if (vinfo.bits_per_pixel == RGB_FMT_888){unsigned int *p = pmem;*(p+vinfo.xres_virtual*y+x) = col;}else if (vinfo.bits_per_pixel == RGB_FMT_565){unsigned short *p = pmem;*(p+vinfo.xres_virtual*y+x) = col;}
}void draw_x_line(int x1,int x2,int y,unsigned int col)
{if(x1 >= vinfo.xres || x2 >= vinfo.xres || y >= vinfo.yres){return;}for(int i = 0;i < x2 - x1;++i){if(vinfo.bits_per_pixel == RGB_FMT_888){unsigned int *p =pmem;*(p+vinfo.xres_virtual*y+(x1+i))= col;}else if(vinfo.bits_per_pixel == RGB_FMT_565){unsigned short *p = pmem;*(p+vinfo.xres_virtual*y+(x1+i))=col;}}}
void draw_y_line(int x,int y1,int y2,unsigned int col)
{if(x >= vinfo.xres || y1 >= vinfo.yres || y2 >=vinfo.yres){return;}for(int i = 0;i < y2-y1;++i){if(vinfo.bits_per_pixel == RGB_FMT_888){unsigned int *p = pmem;*(p + vinfo.xres_virtual*(y1+i)+x) = col;}else if(vinfo.bits_per_pixel == RGB_FMT_565){unsigned short *p =pmem;*(p+vinfo.xres_virtual*(y1+i)+x) = col;}}
}void draw_rect(int x, int y, int w, int h, unsigned int col) 
{if (w <= 0 || h <= 0) return;  // 宽度或高度无效draw_x_line(x, x + w - 1, y, col);        // 上边draw_x_line(x, x + w - 1, y + h - 1, col);// 下边draw_y_line(x, y, y + h - 1, col);        // 左边draw_y_line(x + w - 1, y, y + h - 1, col);// 右边
}void draw_circle(int x, int y, int r, unsigned int col)
{int x0 = 0;int y0 = 0;int si = 0;for (si = 0; si <= 360; si++){x0 = r * sin(3.14 * 2 / 360 * si) + x; y0 = r * cos(3.14 * 2 / 360 * si) + y;draw_point(x0, y0, col);}
}int get_bmp_head_info(const char *bmpname, Bmp_file_head_t *pheadinfo, Bmp_info_t *pbmpinfo)
{FILE *fp = fopen(bmpname, "r");if (NULL == fp){perror("fopen error");return -1;}fread(pheadinfo, sizeof(Bmp_file_head_t), 1, fp);fread(pbmpinfo, sizeof(Bmp_info_t), 1, fp);fclose(fp);return 0;
}void draw_bmp(int x, int y, char *bmpname)
{Bmp_file_head_t headinfo;Bmp_info_t bmpinfo;get_bmp_head_info("./1.bmp", &headinfo, &bmpinfo);int fd = open(bmpname, O_RDONLY);if (-1 == fd){perror("open bmp error");return ;}lseek(fd, 54, SEEK_SET);unsigned char *buff = malloc(bmpinfo.biHeight*bmpinfo.biWidth*bmpinfo.biBitCount/8);read(fd, buff, bmpinfo.biHeight*bmpinfo.biWidth*bmpinfo.biBitCount/8);close(fd);unsigned char *p = buff;unsigned char r, g, b;for (int j = bmpinfo.biHeight-1; j >= 0; j--){for (int i = 0; i < bmpinfo.biWidth; i++){b = *p;++p;g = *p;++p;r = *p;++p;if (vinfo.bits_per_pixel == RGB_FMT_888){unsigned int col = (r << 16) | (g << 8) | (b << 0);draw_point(i+x, j+y, col);}else if  (vinfo.bits_per_pixel == RGB_FMT_565){unsigned short col = ((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3);draw_point(i+x, j+y, col);}}}free(buff);}void draw_word(int x, int y, unsigned char *pword, int w, int h, unsigned int col)
{for (int j = 0; j < h; j++){for (int i = 0; i < w; i++){unsigned char tmp = pword[i+j*w];for (int k = 0; k < 8; k++){if (tmp & 0x80){draw_point(x+i*8+k, y+j, col);}else{}tmp = tmp << 1;}}}
}

//framebuffer.h文件：#ifndef __FRAMEBUFFER_H__
#define __FRAMEBUFFER_H__#define RGB_FMT_888 32
#define RGB_FMT_565 16#pragma pack(1)//bmp文件相关信息
typedef struct tagBITMAPFILEHEADER {short    bfType;         // 文件类型标志int      bfSize;         // 文件大小，单位为字节short    bfReserved1;    // 保留字节short    bfReserved2;    // 保留字节int      bfOffBits;      // 数据偏移量，即实际图像数据开始的位置
}Bmp_file_head_t;
//bmp图像信息
typedef struct tagBITMAPINFOHEADER {int   biSize;         // BITMAPINFOHEADER的大小，单位为字节int    biWidth;        // 位图的宽度，单位为像素int    biHeight;       // 位图的高度，单位为像素short    biPlanes;       // 目标设备的位平面数，必须为1short    biBitCount;     // 每像素位数（颜色深度）int   biCompression;  // 图像压缩类型int   biSizeImage;    // 图像大小，单位为字节int    biXPelsPerMeter;// 水平分辨率，单位为像素/米int    biYPelsPerMeter;// 垂直分辨率，单位为像素/米int   biClrUsed;      // 实际使用颜色数int   biClrImportant; // 重要颜色数
}Bmp_info_t;
#pragma pack()extern int init_fb(char *devname);
extern int uninit_fb();
extern void draw_point(int x,int y,unsigned int col);
extern void draw_x_line(int x1,int x2,int y,unsigned int col);
extern void draw_y_line(int x,int y1,int y2,unsigned int col);
extern void draw_rect(int x,int y,int w,int h,unsigned int col);
extern void draw_circle(int x, int y, int r, unsigned int col);
extern int get_bmp_head_info(const char *bmpname, Bmp_file_head_t *pheadinfo, Bmp_info_t *pbmpinfo);
extern void draw_bmp(int x, int y, char *bmpname);
extern void draw_word(int x, int y, unsigned char *pword, int w, int h, unsigned int col);#endif

//main.c文件：#include <stdio.h>
#include "framebuffer.h"/*
1. 打开显示设备(/dev/fb0)
2. 获取显示设备相关参数（分辨率，像素格式）
3. 建立显存空间和用户空间的内存映射
4. 向映射的用户空间写入RGB颜色值
5. 解除映射关系
6. 关闭显示设备
*/unsigned char D[2*33]={/*--  文字:  D  --*/
/*--  仿宋24;  此字体下对应的点阵为：宽x高=16x33   --*/
0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xFF,0x80,0xFF,0xE0,
0x38,0x78,0x38,0x3C,0x38,0x1C,0x38,0x1E,0x38,0x1E,0x38,0x1E,0x38,0x0E,0x38,0x0E,
0x38,0x0E,0x38,0x0E,0x38,0x0E,0x38,0x0E,0x38,0x1E,0x38,0x1E,0x38,0x1E,0x38,0x1C,
0x38,0x3C,0x38,0x78,0x38,0xF0,0xFF,0xE0,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
0x00,0x00};int main(void)
{int ret = init_fb("/dev/fb0");if (ret < 0){return -1;}//4. 向映射的用户空间写入RGB颜色值//draw_point(400, 300, 0x00FF0000);draw_x_line(200,500,200,0xFF00FF00);draw_y_line(300,100,500,0xFFFFFFFF);draw_rect(100,100,200,150,0xFFFFFFFF);draw_circle(100, 100, 50, 0xFF0000); // draw_bmp(0, 0, "./1.bmp");//draw_word(200, 300, D, 2, 33, 0x00FF0000);uninit_fb();return 0;
}