Нарисовать прямоугольник, который движется по синусоиде вдоль экрана

uses Graph,crt;
type
points = record
x,y:integer;
end;
rectpoints = array[1..4] of points;
procedure drawrect(rect:rectpoints;xofs,yofs:integer);
var i:integer;
begin
for i:=1 to 4 do
 if i < 4 then line(rect[i].x+xofs,rect[i].y+yofs,rect[i+1].x+xofs,rect[i+1].y+yofs)
 else line(rect[i].x+xofs,rect[i].y+yofs,rect[1].x+xofs,rect[1].y+yofs);
end;
function DegToRad(deg:integer):real;
begin
DegToRad:=(deg*pi)/180;
end;
Procedure rotatepoints(var points:rectpoints;angle:integer);
var
i:integer;
rad,x0,y0:real;
begin
rad:=DegToRad(angle);
for i:=1 to 4 do begin
x0:=points[i].x*cos(rad) - points[i].y*sin(rad);
y0:=points[i].y*cos(rad) + points[i].x*sin(rad);
points[i].x:=round(x0);
points[i].y:=round(y0);
end;
end;
var
x1,y1,x0,y0,rw,rh,rotateangle,gd,gm,error:integer;
xStep,SinAmp,SinAngFreq,yOffset,xOffset:integer;
ar,r:real;
rect:rectpoints;
begin
gd := detect;
initGraph(gd,gm,'');
error:=GraphResult;
if error <> 0 then begin
   writeln(GraphErrorMsg(error));
   halt;
end;
rw:=50;
rh:=25;
 
x0:=0;
y0:=0;
x1:=rw;
y1:=rh;
 
rect[1].x := x0 - rw div 2;
rect[1].y := y0 - rh div 2;
rect[2].x := x0 + rw div 2;
rect[2].y := y0 - rh div 2;
rect[3].x := x0 + rw div 2;
rect[3].y := y0 + rh div 2;
rect[4].x := x0 - rw div 2;
rect[4].y := y0 + rh div 2;
rotateangle:=20;
xStep:=5;
SinAmp:=100;
SinAngFreq:=5;
setwritemode(1);
xOffset:=0;
yOffset:=getmaxY div 2;
repeat
rotatepoints(rect,rotateangle);
drawrect(rect,xOffset,yOffset);
delay(100) ;
drawrect(rect,xOffset,yOffset);
inc(xOffset,xStep);
yOffset:=round(sin(xOffset*SinAngFreq)*SinAmp)+getmaxY div 2;
if(xOffset >= getmaxx) then xOffset:=0;
until keypressed;
closeGraph;
end.