Mine

SetEnv fvwm_icon_size 100
DestroyFunc Thumbnail
AddToFunc Thumbnail
+ I PipeRead "echo $[w.id] >> $[FVWM_USERDIR]/.icons"
+ I Raise
+ I ThisWindow (!Shaded, Iconifiable, !Iconic) PipeRead "$[FVWM_USERDIR]/scripts/thumb $[w.id] $[fvwm_icon_size] /dev/shm/icon.tmp.$[w.id].png $[w.miniiconfile]"
+ I Iconify

DestroyFunc DeThumbnail
AddToFunc DeThumbnail
+ I PipeRead "echo WindowStyle Icon \\$\\[Icon-$[w.id]\\]"
+ I Exec exec rm -f /dev/shm/icon.tmp.$[w.id].png
+ I PipeRead "sed -ie '/$[w.id]/d' $[FVWM_USERDIR]/.icons"

*FvwmEvent: deiconify DeThumbnail

# This will remove gaps when de-iconifying an application
AddToFunc DeiconifyAndRearrange
+ C Iconify off
+ C All (CurrentPage, Iconic) PlaceAgain Icon
AddToFunc IconFunc
 + C DeiconifyAndRearrange
 + M Raise
 + M Move
 + D DeiconifyAndRearrange