############################
# This tcl script uses sasa command to estimate surface area of whole oil droplet, and the contact areas of oil-water and oil-surface. 
# command [measure sasa]
# 'measure sasa 1.4 $A -restrict $B' means sasa only calculates the restrict region $B of selected entity $A
# with a probing radius of 1.4 angstrom (water) 
#
# polar oil: OTT
# surface: KER
# water: SOL
# created by Zelong Zhang in 2020
# https://er1czz.github.io/vmd/
############################
set output [open "sasa_out.txt" w]
set frames [molinfo top get numframes]
# loop
for {set i 0} {$i < $frames} {incr i} {
	set oil [atomselect top "resname OTT" frame $i]
	set ok [atomselect top "resname OTT KER" frame $i] 
	set ow [atomselect top "resname OTT SOL" frame $i]
	set sasa_total [measure sasa 1.4 $oil]
	set sasa_dome [measure sasa 1.4 $ok -restrict $oil ]
	set sasa_bottom [measure sasa 1.4 $ow -restrict $oil ]
	puts $output "$i $sasa_total $sasa_dome $sasa_bottom"
	puts "Frame: $i $sasa_total $sasa_dome $sasa_bottom"
}
puts "Bingo!"
puts "Your data have been saved to the output file: sasa_out.txt"
puts "data format as:"
puts "Frame id, oil total, oil-water, oil-surface (unit: angstrom^2)"
close $output