How to fix these two angled boundaries in Maple

Question

I have this animation done on Maple. I want the two sides which meet at a point to be fixed. The same way the other two straight sides are. Is it possible in Maple, and if not, is it possible to do it in MatLab and how?

with(plots):
animate(plot3d,[sin(Pi*(t-x))*sin(Pi*y)*Heaviside(t-x)-sin(Pi*(t+x))*sin(Pi*y)*Heaviside(t+x),x=0..4,y=piecewise(x>=0 and x<2,1/2-x/4,0)..piecewise(x>=0 and x<2,1/2+x/4,1)],t=-2*Pi..2*Pi, frames=90);

Thanks a lot.

Answer 1

The original,

with(plots):

animate(plot3d,
    [sin(Pi*(t-x))*sin(Pi*y)*Heaviside(t-x)
     -sin(Pi*(t+x))*sin(Pi*y)*Heaviside(t+x),
     x=0..4,
     y=piecewise(x>=0 and x<2,1/2-x/4,0)
       ..piecewise(x>=0 and x<2,1/2+x/4,1)],
    t=-2*Pi..2*Pi, frames=90);

Is this what you're after?

with(plots):

adjustor:=sin(Pi*piecewise(x>=0 and x<2,(y-1/2)/(x/2)+1/2,y)):

animate(plot3d,
        [sin(Pi*(t-x))*adjustor*Heaviside(t-x)
         -sin(Pi*(t+x))*adjustor*Heaviside(t+x),
         x=0..4,
         y=piecewise(x>=0 and x<2,1/2-x/4,0)
           ..piecewise(x>=0 and x<2,1/2+x/4,1)],
         t=-2*Pi..2*Pi, frames=45);