circle.c

在嵌入式ARM板at91rm9200(型号ts-7300)下画一个圆并在屏幕上显示的源程序。

#include<unistd.h>
#include<sys/types.h>
#include<sys/mman.h>
#include<sys/time.h>
#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<math.h>

volatile unsigned short *regs;

unsigned short *fb;
unsigned int yoffsets[639]; 

void setpixel(const int x, const int y, const unsigned short clr)
{
  register unsigned int p;
  p=x+yoffsets[y];
  if ((p>=0) && (p<=307199)) {// 307199 = 640*480-1
	fb[ p ]=clr;
  }

}

void clearvideo(unsigned short clr)
{
  register int idx;
  for(idx=0; idx<307200; idx++) { // 307200 = 640*480
       fb[idx]=clr;
  }
}


int imax(const int a, const int b)
{
    if (a>b) {
	return a;
    }
    else
    {
        return b;
    }
}

void linedda(const int xa, const int ya, const int xb, const int yb, const unsigned short clr)
{
  double dx=(double)(xb-xa);
  double dy=(double)(yb-ya);
  double x=(double) xa;
  double y=(double) ya;
  int adx,ady,k,steps;
  adx=abs(dx);
  ady=abs(dy);
  steps=imax(adx,ady);
  setpixel( (int)(x+0.5), (int)(y+0.5), clr);
  if (steps>0) {
    dx /=steps;
    dy /=steps;
    for(k=0; k<steps; k++) {
      x += dx;
      y += dy;
      setpixel( (int)(x+0.5), (int)(y+0.5), clr);    
    }
  } 
}


int main(int argc, char **argv) {
        float rx,ry,px,py, pi;
        unsigned short c;
        unsigned int idx, ix,iy,cx,cy;

        // slight speed up for setpixel calls 
        for(idx=0; idx<640; idx++) yoffsets[idx]=idx*640;

	int fd = open("/dev/mem", O_RDWR|O_SYNC);
	regs = (unsigned short *)mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x21800000 );
	fb = (unsigned short *)mmap(0, 640 * 480 * 2, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0x21800000 );
	regs += (0x30 / sizeof(unsigned short));
	regs[4] = 0x301;
        pi=0.0;        
        rx=319;
        ry=239;
        
        ix=px;
        iy=py;
        clearvideo(0);

        c=0x0001;

        px=sin(pi)*rx;
        py=cos(pi)*ry;
        cx=(int)px;
        cy=(int)py;


        while ((rx>1) && (ry>1)) {
           px=sin(pi)*rx;
           py=cos(pi)*ry;
	   ix=320+(int)px;
           iy=240+(int)py;
           linedda(cx,cy,  ix,iy,c);
           cx=ix;
           cy=iy;
           c=c+0x8;
           pi=pi+0.2;
           rx=rx-0.025;
           ry=ry-0.015;
        }
 
	regs[4] = 0x300;
	close(fd);
        return 0;
}