buf

function buf
global fx hf xys vx vy xa1 ya1 t dt hfl00 g xyh th hsm hlg
global m k isk vw isvw

set(hf,'WindowButtonMotionFcn','');

if hlg==hsm
    vx=(xyh(1,end)-xyh(1,1))/(th(1,end)-th(1,1));
    vy=(xyh(2,end)-xyh(2,1))/(th(1,end)-th(1,1));
end

tic;
dt=0;
t=0;
fx=false;
while xys(2,:)>=0

        if ~isk
            vy=vy-g*dt;
        else
            if isvw
                vx=vx+(-(vx-vw)*k/m)*dt;
                vy=vy+(-(vy*k/m)-g)*dt;
            else
                vx=vx+(-(vx)*k/m)*dt;
                vy=vy+(-(vy*k/m)-g)*dt;
            end
        end
        xys(1,:)=xys(1,:)+vx*dt;
        xys(2,:)=xys(2,:)+vy*dt;
       

    dt=toc-t;
    t=t+dt;
    update_in_main;
    % update in small:
    xa=xys(1,:)+xa1;
    ya=xys(2,:)+ya1;
    set(hfl00,'Xdata',xa,'Ydata',ya);
    
     if xys(2,:)<=0
            vy=0;
            vx=0;
            xys(2,:)=0;
            break;
        end
    
    drawnow;
    end

% reset hystory:
xyh=[];
th=[];
hlg=0; % hystory length