Frambuffer的学习

Frambufffer也称为帧缓存、帧缓冲，是Linux内核中将显存进行抽象后的一块缓存（内存），目的是为了给用户态进程提供一套直接写屏的接口，而不用关心物理显存的位置、换页机制等具体的细节问题，允许上层应用程序在图形模式下直接对显示缓冲区进行读写操作。

由于显存空间无法直接访问，故采用内存映射的方式进行访问显存空间：

内存映射的方式：

1.打开显示设备；

2.获取显示设备的相关参数；

3.建立内存映射；

4.写入RGB颜色值；

5.解除映射；

6.关闭显示设备；

#include "framebuffer.h"
#include <linux/fb.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <math.h>void *pmem;
struct fb_var_screeninfo vinf;int init_fb(char *devname)
{//1. 打开显示设备int fd = open(devname, O_RDWR);	if (-1 == fd){perror("fail open fb");return -1;}//2、获取显示设备相关参数 分辨率 位深度int ret = ioctl(fd, FBIOGET_VSCREENINFO, &vinf);if (-1 ==ret){perror("fail ioctl");return -1;}printf("xres = %d, yres = %d\n", vinf.xres, vinf.yres);printf("xres_virtual = %d, yres_virtual = %d\n", vinf.xres_virtual, vinf.yres_virtual);printf("bits_per_pixel : %d\n", vinf.bits_per_pixel);size_t len = vinf.xres_virtual * vinf.yres_virtual * vinf.bits_per_pixel/8;//3, 建立显存和用户空间的映射关系pmem = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);if ((void *)-1 == pmem){perror("fail mmap");return -1;}return fd;
}void draw_point(int x, int y, unsigned int col)
{if (x >= vinf.xres || y >= vinf.yres){return ;}if (vinf.bits_per_pixel == RGB888_FMT){unsigned int *p = pmem;*(p + y * vinf.xres_virtual + x) = col;}else if (vinf.bits_per_pixel == RGB565_FMT){unsigned short *p  = pmem;	*(p + y * vinf.xres_virtual + x) = col;}return ;
}void uninit_fb(int fd)
{size_t len = vinf.xres_virtual * vinf.yres_virtual * vinf.bits_per_pixel/8;munmap(pmem, len);close(fd);
}void draw_clear(unsigned int col)
{for (int j = 0; j < vinf.xres; j++){for (int i = 0; i < vinf.yres; i++){draw_point(i, j, col);}}
}void draw_h_line(int x, int y, int len, unsigned int col)
{for (int i = x; i < x+len; i++){draw_point(i, y, col);}
}
void draw_s_line(int x, int y, int len, unsigned int col)
{for (int i = y; i < y+len; i++){draw_point(x, i, col);}
}void draw_rectangle(int x, int y, int w, int h, unsigned int col)
{draw_h_line(x, y, w, col);draw_s_line(x, y, h, col);draw_s_line(x+w, y, h, col);draw_h_line(x, y+h, w, col);
}void draw_x_line(int x1, int y1, int x2, int y2, unsigned int col)
{int x = 0;int y = 0;if (x1 == x2){if (y2 > y1){draw_s_line(x1, y1, y2-y1, col);}else{draw_s_line(x2, y2, y1-y2, col);		}}double k = (double)(y2-y1)/(double)(x2-x1);double b = y1 - k*x1;for (int x = (x1 > x2 ? x2 : x1); x <= (x1 > x2 ? x1 : x2); x++){y = x * k + b;draw_point(x, y, col);}return ;
}void draw_circle(int x0, int y0, int r, unsigned int col)
{int x = 0;int y = 0;for (double si = 0; si <= 360; si+=0.01){x = r * cos(2 * 3.14159/360 *si) + x0;y = r * sin(2 * 3.14159/360 *si) + y0;draw_point(x, y, col);draw_point(x-1, y, col);draw_point(x+1, y, col);draw_point(x, y-1, col);draw_point(x, y+1, col);}}void draw_bmp(int x, int y, char *picname, int w, int h)
{int fd = open(picname, O_RDONLY);if (-1 == fd){perror("fail open bmp");return ;}lseek(fd, 54, SEEK_SET);unsigned char r, g, b;unsigned char *buff = malloc(w*h*3);read(fd, buff, w*h*3);unsigned char *p = buff;for (int j = h-1; j >= 0; j--){for (int i = 0; i < w; i++){b = *p; p++;g = *p; p++;r = *p; p++;if (vinf.bits_per_pixel == RGB888_FMT){unsigned int col = (r << 16) | (g << 8) | (b << 0);draw_point(i+x, j+y, col);}else if (vinf.bits_per_pixel == RGB565_FMT){unsigned short col = ((r >> 3) << 11) | ((g >> 2) << 5) | ((b >> 3) << 0);draw_point(i+x, j+y, col);}}}free(buff);close(fd);
}void draw_word(int x, int y, unsigned char *word, int w, int h, unsigned int col)
{for (int j = 0; j < h; j++){for (int i = 0; i < w; i++){unsigned char tmp = word[i+j*w];for (int k = 0; k < 8; k++){if (tmp & 0x80){draw_point(i*8+k+x, j+y, col);}else{//文字的背景色}tmp = tmp << 1;}}}
}int draw_utf8(UTF8_INFO *info, int x, int y, char* zi, unsigned int col, unsigned int col1)
{unsigned long  out = 0 ;int ret = enc_utf8_to_unicode_one((unsigned char*)zi,&out);unsigned char* data = get_utf_data(info,out);unsigned char temp = 0 ;unsigned int i,j,k;unsigned int num = 0;for(i=0;i<info->height;i++){for(j=0;j<info->width/8;j++){temp = data[num++];for(k=0;k<8;k++){if(0x80&temp){draw_point( x+k+j*8, y+i, col);}else{//   draw_point( x+k+j*8, y+i, col1);}temp= temp<<1;}}}return ret;
}int draw_utf8_str(UTF8_INFO *info, int arg_x, int arg_y,  char* zi, unsigned int col, unsigned int col1)
{char* temp = zi;unsigned int x = arg_x ;unsigned int y =  arg_y;while(*temp != '\0'){int ret = draw_utf8(info, x, y, temp, col, col1);x += info->width;if(x > vinf.xres){x = 0;y += info->height;if(y > vinf.yres){y = 0;}}temp += ret;}return 0;
}