Bartlett-Hann window 31/50 - (12/25) abs x + (19/50) Cos[2 Pi x] on [-1/2 1/2]
BartlettHannWindow[x]
Plot[BartlettHannWindow[x], {x, -1, 1}]
→ -Graphics-Plot3D[BartlettHannWindow[x]BartlettHannWindow[y], {x, -1, 1}, {y, -1, 1}, PlotRange -> All]
→ -Graphics3D-BartlettHannWindow[0.1]
→ 0.87942645786248