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1
short 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;
}