dim 110 125 

point A 30 60
point B 80 60
midpoint S A B

point CC 0 100 100 100
getx ind CC

if_then_else { ind<50 }
{
   if_then_else { ind<25 }
   {
     expression phi { (50-ind)*2.2 }
     rotate C S phi B
   }
   {
     expression phi { ind*2.2 }
     rotate C S phi B
   }
}
{
   rotate C S 110 B
}
%point C cx cy

distance ac  A C
distance bc  B C
distance ab  A B

if_then_else { ac==0 }
{ set_equal AC1 A }
{ turtle AC1 C A 90 ac }

if_then_else { ac==0 }
{ set_equal AC2 A }
{ turtle AC2 A C 270 ac }

if_then_else { bc==0 }
{ set_equal BC1 B }
{ turtle BC1 C B 270 bc }

if_then_else { bc==0 }
{ set_equal BC2 B }
{ turtle BC2 B C 90 bc }

turtle AB1 B A 270 ab
turtle AB2 A B 90 ab

line c A B
if_then_else { bc==0 } { line a B AB2 } { line a B C }
if_then_else { ac==0 } { line b A AB1 } { line b A C }
perp n C c
foot D C c
line c1 AB1 AB2
intersec E c1 n
line e C E

parallel a1 AB2 a
parallel a2 A a
parallel b1 AB1 b
parallel b2 B b

intersec F a1 b1
intersec G a1 b2
intersec H a2 b2
intersec K a2 b1
intersec U b1 a


if_then_else { ind<=50 }
{
color 100 100 255
filltriangle A D E
filltriangle A AB1 E

color 255 125 125
filltriangle E AB2 B  
filltriangle E D B

color 100 100 255
filltriangle A C AC1
filltriangle C AC1 AC2

color 255 125 125
line FG F G 
line AC A C
intersec X FG AC 
line BC B C 
sim X BC X 
sim Y BC G 
filltriangle C B Y
filltriangle C Y X
}
{
if_then_else { ind<=60 }
{
color 100 100 255
filltriangle A D E
filltriangle A AB1 E

color 255 125 125
filltriangle E AB2 B  
filltriangle E D B
}
{
if_then_else { ind<=70 }
{
color 100 100 255
filltriangle A F AB1 
filltriangle A F D
filltriangle A C D

color 255 125 125
filltriangle F AB2 B
filltriangle F C B
}
{
if_then_else { ind<=80 }
{
color 255 125 125
line FG F G 
line AC A C 
intersec X FG AC 
filltriangle C B X
filltriangle G B X

color 100 100 255
filltriangle A K C
filltriangle C K U
filltriangle A C D
}
{
if_then_else { ind<=90 }
{
color 100 100 255
filltriangle A C AC1
filltriangle C AC1 AC2

color 255 125 125
line FG F G 
line AC A C
intersec X FG AC 
line BC B C 
sim X BC X 
sim Y BC G 
filltriangle C B Y
filltriangle C Y X
}
{
color 100 100 255
filltriangle A D E
filltriangle A AB1 E

filltriangle A C AC1
filltriangle C AC1 AC2

color 255 125 125
filltriangle E AB2 B  
filltriangle E D B

line FG F G 
line AC A C
intersec X FG AC 
line BC B C 
sim X BC X 
sim Y BC G 
filltriangle C B Y
filltriangle C Y X
}
}
}
}
}


color 0 0 0

cmark_l A
cmark_rb B
cmark_t C
%if_then_else { ac<bc }
%{ cmark_rb D }
%{ cmark_lb D }
cmark AC1
cmark AC2
linethickness -3
drawsegment A C
normal
drawsegment A AC1
drawsegment AC2 C
drawsegment AC1 AC2
cmark BC1
cmark BC2
linethickness -3
drawsegment B C
normal
drawsegment B BC1
drawsegment BC2 C
drawsegment BC1 BC2
linethickness -3
drawsegment A B
normal
drawsegment A AB1
drawsegment AB2 B
drawsegment AB1 AB2
%cmark_rb E
%cmark_lt F
%cmark_t G
%cmark_t H
%cmark_t K
%cmark AB1
%cmark AB2
%printat_l AB1 {A1}
%printat_r AB2 {B1}

drawsegment D E
drawsegment C D
drawline a
drawline b
drawline a1
drawline a2
drawline b1
drawline b2

animation_frames 100 10