The animate3d command creates 3D animations using graphs of functions depending on a parameter. (See also Section 19.2.2.)
Instead of xstep and ystep, you could use the option nstep=n to specify the number of points used to graph.
animate3d(x^2+a*y^2,[x=-2..2,y=-2..2],a=-2..2,frames=10,display=red+filled) |
The output is an animation beginning with: