float xold=-100,yold=-100;
float x,y,v0=20;
float xmin=0,xmax=50,ymin=0,ymax=50;   
float xn,yn;
void setup() {
  size(1280,900);
  background(255);
  fill(0);
  stroke(0);
}
int k=0;
float a=0.7;
float t=0;
void draw(){
  background(255);
  t=0;  
  while (t<=20)
{ x=xmin;

  y=v0*sin(a)*t-(10*t*t)/2;
  x=v0*cos(a)*t;

  xn=(x-xmin)/(xmax-xmin)*width;
  yn=height-(y-ymin)/(ymax-ymin)*height;
  
  line(xold,yold,xn,yn);
  xold=xn;yold=yn;
  t=t+0.01;
  
   if (keyPressed)
   {
   if (keyCode == UP)
   {
   if (v0>0) v0=v0+0.0001;
   }
   if (keyCode == DOWN)
   {
   if (v0>0) v0=v0-0.0001;
   }
   
   if (keyCode == RIGHT)
   {
   if (a>0) a=a-0.000001;
   }
   if (keyCode == LEFT)
   {
   if (a>0) a=a+0.000001;
   }
   }
   if (key == 'r' || key == 'R'){a=0.7;v0=20;}
}
   textSize(32);
   fill(200,0,0)
   text("v0=="+v0,50,350);
   text("a=="+a,50,420);
}