Tukey (tapered-cosine) window function; TukeyWindow[x] or TukeyWindow[x alpha] (default alpha 2/3)
TukeyWindow[x]
TukeyWindow[x, α]
Plot[TukeyWindow[x], {x, -1, 1}]
→ -Graphics-Plot3D[TukeyWindow[x]TukeyWindow[y], {x, -1, 1}, {y, -1, 1}, PlotRange -> All, Exclusions -> None]
→ -Graphics3D-TukeyWindow[.4]
→ 0.2061073738537635