These bars are moving at a constant speed together, but it looks as if they move to the right in an alternating fashionÂ…
Code:
size={sizex,sizey}={600,400};
n=16;
bars=sizex Subdivide[-1/2,1/2,2n-1];
width=N[bars[[2]]-bars[[1]]];
bars=Rectangle[{#1,-sizey/2},{#2,sizey/2}]&@@@Partition[bars,2];
cols={Lighter[Yellow,1/5],Darker[Blue,1/5]};
heights=N[sizey Subdivide[-1/2,1/2,Length[cols]+1][[2;;-2]]];
ClearAll[CreateScene]
CreateScene[\[Alpha]_]:=Module[{recs},
recs=MapThread[{#1,Rectangle[{\[Alpha] sizex-2 width,#2-width/2},{\[Alpha] sizex+2 width,#2+width/2}]}&,{cols,heights}];
Rasterize[Graphics[{bars,recs},PlotRange->({{-1,1},{-1,1}}size/2),PlotRangePadding->0],"Image",RasterSize->size,ImageSize->size]
]
Manipulate[CreateScene[a], {a, -0.6, 0.6}]
enjoy!
