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;
}