From 8d855be27a3a5f1aa58cb773a9745151592b5160 Mon Sep 17 00:00:00 2001
From: Humza Shahid <humzasaur@gmail.com>
Date: Sat, 9 Aug 2025 08:15:11 +0100
Subject: [PATCH] add layer field to app type, as preparation for switching to
 layer tree

---
 dotscape             | Bin 1051816 -> 1051816 bytes
 fcore/app-init.sml   |   1 +
 fcore/app-type.sml   |   1 +
 fcore/app-with.sml   | 100 +++++++++++++++++++++++++++++++++++++++++++
 fcore/layer-tree.sml |   9 ++--
 5 files changed, 108 insertions(+), 3 deletions(-)

diff --git a/dotscape b/dotscape
index 036a86206742de22faa4bd00530ab00a8daf020e..f8ca62f4c9bc860a1613a52c7a5e7593c809b93a 100755
GIT binary patch
delta 11798
zcmbtZ4Oo=Nwf@e`$ImW^K=_k1u)8248kDvEVG0XrjlsmIrRr6SyX#L71%V{Q&|F<0
zQLjnS^)rmIMt6x(7E)BU^;44=wb4-X)E`W&wTazDW30E;U{Zyc>OHgj?fS`0o}1^n
z`#j6pnRn)#GiS~@b7p9H-PH2BY4;=&cW^-7yoA9SgFjq6d)0_{iyA)t%c%_aToOGZ
zw7YBlbVI4TI;Sy&I7Uij><psIk!FuQ0})d8xMdLG-a2kNA)b-ajodldH)TRSSvXqi
znlKh2?IT}>lTs?({b?7BlDd92nKx1=*1{O~=84Y(lGsTNoHRWihD6$0Gyxmui+s@Z
zCk})V^H6uxbR%$D`15+g>9Jp|2IMwn=JUS4Bi#R*84*b=L)~P-O+qflxW8F+1BfTa
zeXVpIL4od-OEv%({6KjfaYVbD%5RFq8{=-QexIVWDK(P^!YKFVmq*1DGj*TbY#=a1
zy0L|6my;ghV_Ka5B5_M^)B$N8?oQZ-s-2S>9nHj$E*YH@NxD(0bvAJl+uTg_Mrm*J
zP8cnfyxC0BjBc`hK7^TRk2ix9OP;^SxovO7;9{sG?I<MssPyL@W4O?PI}Z|gLOS8v
zG3N3kwyw~Zpx4<XxGc7Lz4~tp&g6eUdrUc`IKPwj)ICg!=L@F30{nhON$bC;(Au3Q
zwYKIF#~|ryYqG&>uyr}LLZ2ns)aR@Rm-C2VcUT2`bEvJWxt_Q@p;AWMs6kJV9*88x
z1o=2d*t#5RLtKt-uy?0R)oqWWGJD&aj6r2K+^>uy&aaFmR#8SY^<6?mE~iN=-p(eD
zRCoK^xd3MO-+vncS-LP=mxl;_=1^0gUa)n6AoO`?T<gFGVWSh5>*dNKW*97`?3(b<
zM%v>UMv7CBhQ}j)mG+o*r1(lE{(ecS*_9uIs#_+JVnEd|7lPe0R%*YI71jKJt&1cH
zu23DWHBP#-E13))Dkbku(Y}>t>k83{uFs89-q(4OZTCX$i)hiw$k0Zm>${WnYjCTJ
zv5B;kQyb~=OeMwoNR!J$<6E~6ld|^gh;n42ouUMn2?f77R=Tif3~@dnC3LL1XQ=+W
zX7L*e=H1&hzGI)KxleR7lkc5pGx_Hg<SFx#Onv@&(uod(`-9)d0a-X!I=?p$i91;y
z0Wsrn*NNcbJ8jMq`Wz2Pv-e>PN*nf-@W8#X?*{1}DP7(_o9J_-!UK1BXW={NN%Kf4
z<y{`RwePNjI7$0nH8<Oe_l(3aRO)!|0$DIt+HmkZ(T$fX-hT&@rL04bVrW+!!ibHK
zY7YCt{hPy>7N~prkpx04!`)>c3<Mxj?a>hfh+nNk=!_Oo+IuvGSgCaOsDU^|>6@b&
z1}DV<xkBIJEK{Ej9m7XO)W49}4`mB|I#DV-)&P;xv14f{@9MD<q8}p_eK;i8)%0OW
zhGh)86-JFki#{KU?nIEHTX~T?gbOZW7VKV8O72XB5Gl9QK=k=iNoNMJB)V61b`j!8
zmu7$T6pwiGOtd^ky!)fifmnx2oBuQ!#a{lC&xjLG{2UvbPrQSFXPoTdCe)t7E_cbP
zX269@DHn>|Pju-C;uRnJaKk50Azu9nB`^$S6uS5Q`CEl?vUKV%IXIG>SC|{6jpy~)
zvG+U|Q2kdQgN#qPfZ9(30$TYt9>4GycE<j#9f(sW9q}9?j^XZA-Y;l)9GVkd)Z%{b
z^ErepjFq~+$Rhe&_nj{WQZ42YbGpFuh&%DW{|HfLjJ`nNWAt77$FM;-L<sc_=`n=~
zz8LdRvDIpjjQ^B51B~S2d7V`H>YpbxskSarL}3Q$__ZAb$5dY*>k|V0G4AVI`559K
z(|#wxUHRo}pxJ_IJSY^WI;5x@>v%MKNBAZEfM`zDj8=mAVP7zpe)Tx#aCqns=79O&
zCkl%!WU&mUO6_0Y=1dAE`<YzvCzYsMSy>KDDmtCu!mqsrZJQ~8D=ivxS%|5RVj4*M
zk<gch&XqY-in^Ih97buytqf`EO`WzIlZ7EE#ML}jI&mwTy!C)|=T@@x!OihpQeENy
zThhZQX`<Hp9a5TC>af?dR&-si$Lx3n>{oF?&0}p{-K`-m?--$P#htr}L^QenuW<+d
z`NPKTLVf~T1N;Y8qVL2K&{6n_Wuihc2hmH$^iAOIVH)grk6-ou8_x=<_M4Bm+Z__o
zC2+haL@3tdc%FFY8>EukGsprx=HCqI)7vq8x)3fDuS6HVb-N6>dxZqtE5p71-|_c%
zl_luW7GAW)6|{vHZSfDEEu`$b8Q%lB%kD0MSRD_ISbsi!%OKd(2fx-0i^!#PRs=91
zhr1l=$xlxwqFmQYXkbx<-e$}{zOx9`igyThg0AC?V|xJ_6S%=0p@PeaS=!Mo*g5Cz
zW98Wdp2nOZ9}(dJ%&P2c2w-I;PYi{pd9ytXa*0DPUkwAy0{WqHqXs_2@oYvUd;vtx
z8vtn{Hmxymi{~)YaJ2l3M4lfDp%nR)#RH=-L?(mq92y!;dmK*+#o-vE`QaFePauuN
zKBRn`CMCkguDf>=^W)^T4+54u5i)rQ9`nu9rQDn6`H_E~?jirYDG9Lgw0~Z8s((3{
z%+3IpXV%=Cr^DUj^2|uNywUNn@sfYu*)+(e*_K%Uk>SAn&F$*NfQLwbPB-xKA)L74
zbzrA9%;^uy#v$+rsu^VK+RjfugM23o$|&j9%4OLQN{DkHs~!m@#F@vsMnVx%IVA@S
zKpc5;p%FrTKZ-^H2_?;W@|5u~9SglY)|?9m_>htbP$&|8n%tZZ#|Y7-$z_G`Q8*f9
z%w!;VaOAPvCt)uF44I_J(No|F%7v6ngE<5`*@2%!7H4$%=Uf(YzE%t;__Tw+fF@37
z%z(38yX=`@<?RhK{o3A`3CH=wgR@`?X8AlhYBt3Bei-J!gS?1j`E#Lz)34?NuO`{p
zUqUUmW%n=PKnVIn#eDd0B(oPl8<Nn4@ILB&Y$2@UzBZ#2W}?%`?MtD7JBhIpt|MiJ
zXW@(3573D)`==r;<@8-5KlmJ=n?}er&%+YJ2bg)hBJJe#UBbS40S>?iti2XS5gdQ9
z7Kj!IyZjOidnnS@WsAivOyGySZ8{$G`|G*|yCqrZ(<jQ=FT)JHLL|tmR>MS^V8BD$
zfQLEBH1*BHk?>=o54W*<E#SEw#X?^JtZU@FSGZlQgIVLNU?i3VcH~u<NUTKG{u(Zb
z9Jp$SCAgp&8z9TD05$ljNP0zKW^afvtM_FrHTdraEH#KNvDXm6nm53mEC<%AHiDWO
zeVTUhlEjjYwJCb4cY>{}4xMs7VwO?txP)@e5$ukH(W#?y?nc0Shjlp1Zh|*);ayFT
zwi3%98^*h((9~xZaXJB40UDsrAnZ5KHuc#OkR4(+0(L7dyFp7`csA^}B8Fq^^{Yge
z6X#h)VSS;)Xs^R6y{;bXTO3=rHq>RS4|C}dw@noKwiS}`XxuJd^VHRATy;l?J+A??
zUN;V?Z`8W#v7~CKC-(Zr2v>bK*waFIf23>MdEAX^q0frzD#UfxuMqkgtkiDEXB`Z^
z*P19_U{C{DUNlY}8i&mC7xD#Y95US0_b5(kM&s0@aYV$dqu7eq(KyYKtmAbsB=Zfe
z&%&{#{tc~f20K}bSu%lLdmXY#cZi&_8ImDEj{|*WT#czOA9vndiv?gPoAMhRWDaF3
zeuDv=7R`?T25MrRiRdM`T-*^?J(@~Cl1<-&9^y@BHCtdFZv5FTINY1W3~!)g=#p63
z8;}N(tnm#TH9tx2cmo|8_e+j);C_LTbvR)R@eY@-I-vyPD@rbU6R^OtM9JT5M_)^}
zMDgW=%TkY<Lx{_U9&9edQZ<TMcL0`&tbGSm6Yof7*olFu&tYeGLIZZsZh^<*(E<6=
z4%Zj=@}(WBPwF*m<-IMCfFi=#2^Shb$NuiZ*fz6}R@g<%;cRa!?BHlg8zd96hSee+
zb5Vni!lSA2o{##XsR>PrSUpCSrHNw#IuY0{n=#6??06fLfrE{H8$Q<KQB^k^cf6fn
zByC-MBb`|3)LH#~cwA-u7I)q-RG#r$p0_LmSxGyrCHevEYCBrfGmsf~K?U(dvF2Ua
zc0{nNyKsUhk|pehR2aa<>_!LB4V24v!!a~wm~8BTBM`60^P0PmB^GUn2c;EbOV2dF
zgZacUSg!aTbn!Zx74F5%H9^jnVGi)Snr>TsalVZ*X&>mZWMF&uL6`A!JfcI;r1f|^
zHDKjYh*#x#SRd$I@w`Iq@$QKC6%tm=I$z_Z>r$G0U_Vqtly9l11YbTbHTNCV98c9n
z@8I#n9ir(Vp1VA;-hJPnVBLpc6;G@a4uesQ?Zw=e6;qswG<-19F9}<D6bw<ju{6n!
zDbCD^Db8=9Y}ZkkhFgitpUbBls*CqcS+f!;PFZ#gP7|G8F8mONk--kUfR2eP&Kw_C
zoWF_mIE`_<ws6gV$>dronBL37uQyfR@JC3&Lr5ogd;~K|d<?o2=0+QOzq!zVr}oCk
zDJP&6Pqk?I_(?GGAMDO4xXS6(({PQ`^Id%FqFK=yWM__MWoIBcS&!W6Fi3goDG-HI
zddGuypI;1RThG7>;vLFTK1TP}XK^};9sL;ciA8CQ{{%`Qmo<L^O|h16R4Ym7OC2Zd
zPyJFDZyCXg&ccX6=yMPr<{}=j^9_LTa2L@LUK(vU3mLcp?7&&L4HMYjKf_7Ll~<j^
zgOOayVkLhCHyBv#r!Xh#r&u4x#TRGBqCY%B<zIb@5eny6)&<niqnBGRKnA2ZFtPcP
zc*(s0;g!U>6T(J4p1^;@m~*fY52ViUqOx@<=#N$&)1pg<Z5vu)n-#`mtlM=MPqt7@
zv{ta&a<T45>j+pmH(&}g7<v8-b6K%qsaqTF!kl2Yt<tz056iV4%m+TlrGCdf>4ibu
zaj$ye`1d-ld4S(>^%08W<^>#=q2s18%|%EbFj!gJ7<{+MW>G6?3Y&Eip2Y_*`NTzd
zifTsrFI?X2)fr!aobd%YzXo5&WKv15hd>O=dV%J$;WhNN!0&Hs=--v!vTixmfWI-3
zd>zB8U!d3He~inc!g~E7t=)H)p=3|CTvJP{(HG<8t1r?-G9aVBT2jBR_LcON0mv$F
zx_VIgH8h!-ZM6J5`sJ@}v<|q7>ujmLJ{QL$ia#5ni?6MxV}a|%nVIp}LcRJde!b2%
z(4F_s!$had+wd}-@ICWb_p0yKZ{zCk(r<N8WuH{vKFEjG(B}X$*qF6+TM$R>l%>kw
zuBC6mLjkp?_|-N~M5;yg{R0oaN_YA!&XXi|;c4%(6#016{+d1wS6KJ2=_tr#35|3L
z(LF3LYNRsZ(g2gV6}9nZ%UO1c2Um9vJHLT;5N{4^lqkNNjAhp(x)uB7#*I`47{(?x
z(VejiF!vnCR}Z8u2a(Pt>~0gar<k#*{;n{(Viq=9(tKe=bPup&jHb-6@Y6#TM;?p`
zbsTx(u>C!8)Scsxqvrl`WR!C^Q6-L^4)YxV>t3h6IBI>Jet#T!o(c0E0M4o~{{fJD
ze;oaBGu81`A6kq|kv?9Ew3NuVH>39x%V-w5g&rj49QoK5iY52pe0Kf~+Q1Khd0Xjp
zUIceI=mC7`8qF%+L<2i=m|;7$@*;56cDjvUnKE|JM*)k#vYixPyyDr~opc0<@`0W7
zBMz@}(Z>Md*@;%%%Lqo==(0grAb9bV;+5}wOk69mNU&J(2@5B;(F|fpU>$9=h;-}N
zoi_RkX5h7N(>X9izWg@L1@cxNGqlq?#Da7e($96WVK>dg7jqr6cF?aNQ=Z|bCn!lD
z!ZKvKifkV(x68Bw_>YwRG>t&IT=))U0O{=fyYvs(-1;6p$*%+zhiOA(1otp}R=_;^
z87nwSC&=TD(0_Adj5$iNetK9we~iuqjS{iuku0|p`y=EFoiv5=o6Mb$=n$W6{zO~x
z?Fk=Y0^a5MiG1M%ZR6nDQykRY2QmZ=@`5f}Nx>n1@(JDOyYMw&<=1SGtN%hL_%0;<
zZ!GWsl{$gEIe=L|L%UrZz}i1UZ;D{wd`9_2=)eVf9r(qu!FO?FJG?Z5o%7J6_xfb)
zdlW4oU%f>CM)0P6{0sUNA>ZO{=qmM6a>>Z<{F9y}=sPE`p$r_E+=JN=jbZ$XCKG<2
zoANK*jT<p+%1t!-jTrgtO}<?>V_0jln8C*N(xn{T(MxY&!j(7o(IViP7k@O#FW#n|
zL}@j$kMGbeN~4T@dY86f&VOx{I7)-Lx4u5q<;ed15%B_WcG*-+X73WQQfaK^k`GW3
z@4dHT*acCX7bRj9vsEb0+>UQC--0|jM4SQxxY_Z#;=4v<u^pk}68@lAhYyNQHYiNo
z$#cn(FmXC`v-oiFZo+m9SrOk?@r|`_r6}|qzInIUnZ~j-VlwGA$`du>2BNu$xdH1{
z*G1VIA&!7z^CB#}&`kgnySdD?-+IurAMbff3QyURtyW=w^G3Yz@Y=8gG4kM0a}Cl8
z(|)t|M?*bW_4AthcRcaq9mW4h0Il+Z0b(y-x?D0)OvNKiUJ)&ZhUES)SqHvfmRYNo
z#SX@c38IH0?{o3uauV1wd3lofqR+@T2Z<d@?>Zt7dBTHYQMeZED*O`gX@$t^(!@WF
zBhExtGFME9<*FaTL~q8Dm*;BF2)1gjXe6F=`M_L}K!P&~ZSs=P%P)(*+IWKr@1Csd
zmtr2#4`Q(;ViwVjV0k5C0-rRaM4Zn(?tod0;13eVO2t-)HS+={84H+PVgI%p!g%ut
zR$nIisxMn;n5(WE?EFpB7K-(Xf!G~!?0A`IAiAOQwK8!O@c)GPUTBbB;V(7#pAZK=
zbOHV+q#F-k$1rxMPE2D9mx}B8Tb$1SR?O}$6{iui-VZ)kE<Qla2DY|b%;$s5{+B>@
zrd&MWdoxClu^L#>OX3juy$bOZ!N&`EU6rWip|<&1@qOSSHm64XFXCU10oPN6>oEdf
z&&}n5^(brbtp_i>R^NK^UJwmo`k}lgi(v1c#Vq^c3*sz4BfK?j%R)vSKEqsoA;2iq
zRfh$g-!O`i;#hWVkdem6NM2eiJ}Ht(RDNfLXrMpLR_=agGO*9;#Sz?AQ4J#g_s?gh
zA*{SXO!AFXY_+aI?6}`ntH|{j*7cG&g<#!hcv-yt1LWte692dShgSRLPg$*!|J&7m
z`3`)|!B<;$a<!OEcqOn}?7F9ie0~i^7e5Ja|Cjg;&xki)72o08*0ElEB^1LhkBM6W
z%R+WxlXw@~7hV^i=UzHvi<rpsd&L{#E#6+_5GRHZXYA_sw?zDg;5QV%VRHLh;pu;1
z2g@~D_U&R#Bzt7BCY*T|YeW{wn`ZtedWj~3g)Y$~u#w9&QLOA4{1v%Wlf)cLaGbeJ
zqYM5DXH&~H(d-oGa%eFQL8ejcLaAmX%PzxdwlYm7pMm$|a!oS(bg4#5!v&EQEY_s5
zD-qGrEP5GAJhe=dKm{R$IhSgF#fq0`e#AyDMOnWq*TiwY;mrK37DX@7#AyWI$Ap8u
zOEmH9JeL~9|1_3qa+{W+l&ecnhj6Yx_G{U4zNT^IsK`AvQLi|*eu?JCENLmuXkCnd
z%;hNY%ZTW32xXRX%|+%wt=PGc=ty?(8BIFNuGAE<-4!UwT&cnGdKvy|=c3kg10AeH
z7Vj=WQBy0hd7%nTkX3=rYtJC?j|$BsKJ5`cIFeN^Lw=qr9EWC!Vr!OSpN$Vj;1O=6
zNM_=8!6EpE1Ey*e>C*)_CW@J#!Erb^n??(i?Wxi{#->(j46Lydw=SCNeXUY6gI%fC
zl(5>R2wYl*Hm$5il><D}`C1eawkpk3+4QWY@;aQ9PD3J`WYgAa6S0K#&etXm8s@jT
zU{&ZOQ<3l2Fcz~w1zQw&QxGmt!_^Ax3Bpxs*w0cBbOizCPBr|W%4~BGKCOnIR$xaE
zhJ`BCN)`CaAe^Iy|3iVt6$WHm)Nri=+k&uN4M!>Pp&)!%4Oc0!@MwT}j~d2jdf#VK
z5Y{hJX)Y@8`XD?_4TmW3sUTdZhT|1D`lkWed(?1}0#6OXUNt;BAUg=hJgrhKJs>*>
z7pUPy3Y_$_fb1$YjQ`T|eau1FsfK@|z>Xk%S`8Bg_5@)lRjD>ufprrDvUAjMqyn3R
zutg2e4ag3{b~TI-jK0s6AbeO2XDD#yV*%McYB)}TOM|d}u}bq<3fvNer>WsV3VbC9
z*QsGF^n9PpNdeh=)G!uCzE5Qk_Nw8>6nJ+Kjww^AHb;SbgK&WwPElaf;{n-KY8dmo
z?_&$XPBomTz=wkHX*C?Cz(P@gIV@4B7NNkVAe_VDTgrmRE%DC^tp66XsNrx0E>-9)
zW>>@K%KWo81>wVLxJ7|GgK&=;Uar8sL0G?3rP?F~&Rpsja*It<!$}G}D+t%A;VX;%
zv(^ORJ!*KL0`CjLUNyW%fv*JNm~xeBvlKX~JfK>E8qQSUNkO<u4fmG%XDtuHPBq-A
zz%4=ev>M)|z~_Q6RH#%dRp9W7fND8vc$@-{3&IvP9In8nLD;T_&pqvDx+w@BR>Lg{
z+!=&>)bMfz?hV5FWh%`lDRAbpfacTGaFPPg3c_`2_{t*xtTjP+j~d>m!25!*R}HUG
z;448mrc$NaECo)g45(J1hBFm-QV_0E!@Udrvz7;8ryA~5;FchKS`BYf;B!G3s#L0#
zDsXsJK(!n-JWhef1!0RC4p-pPAZ%B|=N9;xZVJMO)o_afcLw1eHN0GbdxNmPTBZ3U
z1<tGvXg*C1Cn@l(AY50i9RYT>hmW!=X-$iiS63G0OtmvFhtDYa?20luklxO)m}d}f
zQ`&*EG61)+0yP}12$}SZU&A(5rG{+^yj+1@%=wJ=DUetXj)K>GB*&@n-mPfzywc8m
z*3a`fr5#Yg#il*0O?>=cN_$O_e^>wx^tUMel?t0cf2Y#FM(J;3dpNsaDD(R-I56!>
zKQRFVar5#|KztjEc@FItueA5gzhAp}R)Fxz0N3cr_rvp)X(N?>i_$hL?Et=}U%RDW
z`;^iS$mvzu3cHm;fKk#Degy*Usr}lve(l};+UNSUg(vUlH?m*b>}&s65CWR5Q3fcQ
z1^Zk2_0I#gwnm!*zh<r)?U0yqWqhyVS+B|78f_|A0&IKxO%L`fhH&)riliy`Z$x1H
zxPJX@%(5J}HvrF4;41-VT5Vsh#cu?DBW3&Y0oPvv3#${OR>Hj15E3Or$iTeZ(5fd#
zKl*}E{#pLOn#A<cWuqT|-k5F7o-Zs~ymaB@|9E2h$m;AIrCDKod|dT&^513*{NwNc
E2L+%7ssI20

delta 11814
zcmbtZ4O~>mwZCWP^06x-5Wa0-cTq%=qM!i<3oB`jK}({cXw~2@egpv#F`>rSrwb%%
zNsF%6GR7F)MWZaHXxP@PBvG`{TJ!41Cb8Bgc9(ov+iEeXf!N?XvwL^F@{-@n`@Q}B
zmf4yAnRCvZIp@roq5VZ;`-{ed(@At*nrl(rtr+RKCuXNSdHlp|$e8kD=K>NjF1YQ^
z&e?^loOPKkLBy0Rk(^TE&XwlnyaS??F=+*e&YhEH6JpDiZsyL%vEsZ&@^Oyj%F97W
zJLR)ba*0THzVCu5lIsUEcqe(<8u+er`?Q|`Hc``?c+>i52sYBrqCD(eF7iUNXLbh>
zTaGh)b{6oq@QFs0ljA(~qYZ%Eis$^q`*)o4Uvq|q5qpl4EWSm^?gZzTOK;+Y1n2dN
zO#}rx*Hvu+F8IFX4aAh-Y+Zg!B=!VnOWiSw(u(V6jDRW5?axn$Av1~d+;#(j?@2dz
zFzqGUC%j8b3f`wq>E#9><vM5VE>taEYO%GE-qBK)eH!^_thC17%A2URHsTp89ctSL
z6Q#1<ZREqTPO@hagv=y;o>WpIx&IpNw7e1tC`OX@77`ti{<t@r3mviVC;^*v*0DD`
z^}7~V@N>{_ZxtM7%ff#Bzo))a&_nu+nWUuPEz;NUT~e}0Fb+(`?`M>B{EG@5<zuCe
zj(nmUE?w(LH0ZM|F1uD3Fee%Z?2X{CpAf9Ja=~gCW^uJO5{E59O5Hyp!AANZjFb@M
z<DO`7*_wkKwqCFr(xtln52G@N_P1sQl-Y8xGPY=+GUg~n8PPcK5h}8DthDyk45CYQ
zcD|YmpmYB9SHmFPcAv%NCc=Oz*f^jUEG`g)0XL2A7%>vInjf^dJX~4C%G0H!19|sv
zrhV=QNJ%obp)uHQq<tnGDY=@4zb#Vzfr3a>-8`L?0IL2;Az0lysq<!fcsZ_*#0!pK
zonUPXlLikYl8>{c#DhuNkMk|AAf4!VWxSOCdA?*hxI`O<7M+0%BZze4V4{98ZgmNE
zu|3V(1*pU0q(mQPbhv3u$DW6z^w;)=o3hbP;ex}6f_LkrE3ah}^Drs4YyDkA4c#@f
z&rq=N?ym72TQb&pwyTYN<2;MeH*adbGB4gZ;F~9%?J_vu`b{*DR}9kSL;2V^6XkIb
zsmEO>f`jk0DIJYHOqzEXV^G?1xQqwx&BHfITdwrUk$J?ED;0JR^1;H_FO%|IDd`O!
zxoh6o1Ywf)%{p$jwQpvT-fXGs%`0S&LE3WkGI39mYL2}QQBr!(!x-8%Js7c~RDawX
z?q41+B_`21`$Q}udY!ZKtq}lJT61#T@ZmnSde9loLDHd<NyHE?T|8+Z`VrEXCsPgP
za3shT29Bp22XyEd-c}R_Y=y+ylYx#BE)||?f*|SCsT7oV?Nk}@jFO6eHzqLD`n$4J
z{b+P6j2g2ReLfi7iC~LvWk>E1DmaKqu$o6miKmm{J}LLKf!NceveT)=KEk>Fw2Khk
zcxm3-kMW2%%|Xj!#5>>q7>Ge9ZU4gz6#K~^yhfaM_6h84Kl?iVEj`!8O{hJOL(a1E
zZGa1xlCBgvXS(zR@tSwNxZ%CW5U+cW5*ULr3Y~}l_-}=AqICXGnMg@4E6lT`t(WyU
zaOg4@Q1@pqgVguAfHm*?1$6LjJagp{9E|!)CrbUEbi#dtm~_tdo=<6L7@8AZRPTJ|
z<N1V)4wYP=rW4O(=isL!s21~xX_Ub8h%@eQzlU%gMxQ_MG5W6m{ec7|5rVxWeZ~;M
z8)I%Nb{KM`tbfRy0Y-Ak!ncU@*+0%|9<aDX5rySQXRhxhNK<zs$14PUG|n44ISujA
zbPmQkYybI6&}>69j}%IhcSzwkH}PopjPptQ7SWunQG)qny*HREK6{jNI6n6Oz#&yh
z2YJY01?-VJKfld+Or7E5an+Yo!oNsQH(^fE=>!LUt?g*qGyxnb5g1)T#sP|1Amuy4
zKnnWS)odyJRw6Ntm)3rfDm{Knr)|SrVTccMwCSX?Uu2La!=%A45~a6pP3Dps3jcqS
zMuHv%P172_Mo8N__d}R(n?=VbjhGuxfb|-#r%h*Z^>zd~JlVp)+QB<<M8wSYztDC6
z<J-|4Kz;%m1ANC-ocFvE&`tPxWu!t02hm5e2lBXc7)Se@<39$z!jnQ;^X1#z>3T$T
z2&8uh2_<@@=V>=3M=HBrN<PZN?3*gRe>;*-7ea-Sb?Crf+^z)fTtR;4N_B4jD(2py
z%2*Gs(Sx?Qinj2eE&lGcg_Ln8^&22(<(;Jv<wnM~C|@>x#UNN0r~k4SmXcBFtOy`4
z6Swd<>dDVeJEC0IkI=xP2>orCeY__Tsug1stOPyB9>xv<w8V0Q+kyp$9dop;O|Wv#
zdvx+V0#9MakWYwkALdkcF$l1(lBWg3Q@q<50=dLJUcMFrm;*f7a*GCjhxDv83_b-a
z=MRSz5xeD)@CDCc#s|^z?^AhE6a-V`QyBw{!uMp7fTz&dS81Q^heAmxMrgqvjKi7O
zw&NJKe4D1n!B*FuJ8=aE<>rxq#f~VG`{5DqJYCY=dG7D{=IQSD%`1+DtrvXr>XLoS
z!BqARaCs)p-FZ6PJuc6LEtmID3~c?#H}7H!WY7$KsB(^B_U3lAW4J?@FQXfH@eoQJ
zF*>kPi(vKW<*YIATdIk&xc1=LXUdQV)1i`*@@Tm-1A+<h#Iw5bP)790%rzd0u$7ZC
z!2m>;EEi@$u=hvN1R%l0kSrHZhS`{#lUZ9XbaRrjJSY^2=Rvux08SC&eo(F~gttS{
zDA_ZB;IWa+a(@Vi5Man8NscInnUo7Dn+5av7Ii-X>73CgPjFet`FaVQ<<pM-2wHht
zS_&7rb{TV^ocFiP@o9T=4xHf=kIsc+%<;)`_&kX6{xHmkk-UUt1q+~yx1TKlUQ4o^
zCt(ftW#^O79fY!L7Qx@JnYS4BV-vgtj-lSCmcS<NYo!%12c1UltcE7;Bw4j^16yWz
z8a|B@Fi0`?Cu3W|+kTKoJ_G2cqFnzIs3M%e#N!p))4c5m_Sv)04Fc<20}}|+f4ByS
z7AX7VIe6gyAdAZqg<BZQk9f;$Jm!xy^x}b>hzIm=IpcXKMN>x0>o>qO8e1-6;>4qz
zq!|YmA|*@|25=jDo54WLaV+=+z^X>he}UVjErYfE9I}Wfft~m{Oe4Ki*8T#nh#a_P
zg(_T7=@v*g?1{0szAut~QJB*oB+Tu99t#cry9o;oVu|Z-i)L+GU@+YsjhYhFG|Q{0
zix(v34C8<SJ=JWmxEjzY7a?ZWvojLP)y1$u38T{_%DGzsZyg35%V>q&xNui1q^!f@
z$Aa;0E;Qnafzt^%rlJ8F48jr9JmY{R7TF<YAy{`~rP8FO4m=u;lp}^T*2eXsLqEde
zDi?*#g|;kf1J>vbje@ltX&ah@9hSxrhZ}!erU?VP3dv+NE*}1fHEJ9UCx|t_3A0`~
zGH7hkIvTN{YHB3b#+G4@#$K?dU{&7O66V--8F!-&lNPS45ZBqbRv2h1r`EPK*2U0!
z+eXM&7}P_$J(jNk4K~+T#!p4#kOz$e591^Q8mAGBBO+F=XKP<X<MhU`t{1_O$Tzex
z9ce3k8`{_gR#Ght7!uj_7a@a`YvrWvkO;A6B=i<>^~Qk$+<DU)ECaQy_$4HAYuVbD
zFn~WC!Opw{^-=l=^b%Yy?ueriO=W(F&EA0?qEBb_J76Jh{KXweZjWS!m(elY5v=lM
zNP!^M@-kATM9N(+qeJ6<$>BEKFGyuwcE~376#1GR%JBLaCl~DoEU)Zw@|Szi*Ane<
zeEHxoH{#|H;;^6xn<_C$#j*0efJGwf+zWNYp34mTFfcv2?BYIX!r^)C@JI~qK404L
z#*%)%w4TQJez!(G)DE#Ig0Qm=G=Pcy)q$~XV?iBofY=B-)B$@rTDBh&i7te#!8Ut$
z2s#Rnrk1-t>W!vW+(X0~F{;e1zGAw;09NyMjGqv8W<OMdjy?1$ysO8fs$m{dck*kb
z#l<($jD=1^xo-@QtMp&t&i7`^rN82N%O20lI-!}Equ8}hw5BeBWgUPTqKjv32e5C7
zVb>1uL>J3q4?;4;vh0KC0H%1k@*tc7;=WJL>Vgvx<4NZ>L}^iILw-<VY?+zn*RY6~
zlI5CTgNs+utnd(Kt~5DAhWWs6YPwx9B?S?LNryp?B?CKj7+hJS@uD1rCT+yKsR1jG
zLcAz1>_K8j46jf7JbPojg+w`KozL;gwRo)DeFW+t+`Cj%f-fJJn)^Cxj;HF<*YWt_
z4$*oP&t0Ba?;P_bSZ5Ec=ZQ7%IAn=YGx6|Bk1R>XHgq($-=}QdNx<;M(j+6YBrP+t
zq+m5+2TsB)v^Oq)0iV*-5aXS)aUHfeWyLADKx|{>!r#FIWOO`UKeMAt(k4gaI%%Ih
zE1K69jz!NI9qR<+oB8-PPm#C$9+L0{WQyGNHq0S0!RS($8!hPlrb2#LMt9f~<fOCE
z0r<=zpE(Cv{0AF657&5m?E+lq?PV8kohg(Ry@TxB!&v1zkeF!K;Lc!>^3*d`6wd2y
zBdy#o^qFkuJFu3RGg;ER+`YZ+1a|UWC?FoCGx<HJfHAD?J!p-x6I3f+7)YKZ97+DC
zFxftl6<vgJ3FvbW8sZ>s^hoqI2n}`Mp~Xw1Ef*mbH-L3tgxiqD4*e0%!5De{B|I3(
zo;+6eXK=y;Eb4ujAO1PkhtV-5X;J78e<$*PypItI@htrcYG_NBJFY+~B$;^D<xW<1
zH$ZqLap|nE)jXPA{|m;Pn+3Tcxm3?rorI+2Jf=m54T}#8T47f?OvYHZ>aeh|1Y@Et
z2dgC)%YL+ufR%F-rm)_zJb#8b3^=EuIn;qU!D?BraoF_o8aL(xuj5jm<DT<C0(abN
z9ys%jj%yn3b6ou}#c}ifj?2(-Q<&yM7&RQ<cD!rL#tJ!=g|DMYZ0?8fG(LC9XFr6;
zs3t?XZjITH`YFh%pOVWP@oh{dwe&_11he#KX)b%Pp8nGR```8SugY&(x0-6e*O^9s
zoxtjzr8i>6;qs`kS>L0zde1VHtQ#ZOuc38V5CzNEeoEuW@CifJl7<X*uA?suM^;|t
z`RO`_g>R&Z%w(a<zh+$i+(H|GySUDh-0yX9JfajAZ*HVH!1dzHOvnuN8Zi6xy4Xbb
z-8&BxoicCB^EB@p=CR)OU$5WR4PU3<hJeamsos5%dp6Q%04A{PX1XhY-(9Nw?`HZ6
z-0xSr*r&E>8n#+g-$!`#=X9Uf;@p362v2*5xyWm-HNT)wK{f0B1)YG0N^A=)ChjzO
zX$zGJmj)QD<*1E*jGS(zcyJjC*ySy>i|7kji$u$a{XuqJqC0V1ZrMs@fKhB(E8Q10
z5p&NOeDlDz{V28%Qg)}6T9e#(-Tk^Sx@r=(dQ!Y$MBId(Vl=5#Pw$N*6D9$59GMXR
zrZ_Sb_~NLX$D%5ZOylL;ZB&V)r$W33z@`_eH;y`9q~9Dz?o}b)1HisA#CHJX-Wx~1
z-%fRW)ji9QDYlPRU^|J*x3{DB6Hg8c-a(HNU7mbu2gQ>6l{9wwW!l6KfQ38hY+eL+
z*=RT3Epk}RZZxndj~VvRa$W?k-$QrtD^u!T`Y=9#vC4fE-@8QCypN89Ah~-VeVfDU
z9rO`?vpd`2-Al5cu1LTF!Got1uY4C_;#!AAg1H>);~>_&pQe)DAl9{?7LoFNHn^X@
z0Hay+t8_lz>OOgu<^ma=%nY4$km$!U!vSoU<jaPGG#?{$3M=oTpP|rFCp}Bao>44S
zrt8T^2DwwFHNbx)9ib@%a^%9-DFeu1m*1ej#qQ2G={bHSs5wrX!gy(hr2@~RAF!z>
zX`Vdk1pSH|Bl{%9`YA=ee2UHijS{iCT$Xzp$3^+dX_`d&O=j?II>u|8KhO>cxA_wp
zPtqy!m9um|2b<4x&~y*T5H!e(U9^_Ao<b}B={>sHd*y4w+OIrAuKN?s^Il1Y-dT?Q
znc9JT7|Y5(K+C1XvCa?BpG5ZM2b5ohy06e1z^{%?-m4?q>!GRalAE5qJ0|1U!)OEf
z+DG&+1n=5sKBbQl@;H@8UZWng=6E*v4|<NE_nf<qGLSN{5Az}5#q=|ph_{+#R{SsA
zkFEq(d<)Iql^|cd#W(Cw0_#W=Q`w|`TFueD{q!cLTzUHdEdri<@kgut)7$hkQF<-x
z-9frT=~S}!@6dM4`oCN+PS9ZXZEOs7xKn>~Lc9W;T?Q2s*&9TxRXWXFayJ$6<|`+#
zE26kC{J*e{*(sEy?cuL6RGtwe7Q=9S8RJRbdy&XvdxOO){-D@^4~k}%5F+m5+2lls
zI2+nnOsIG#b}<I6i0`ZT#yYT06#9<ex>MrGXXzR-k+hAMr)k73M6(;ud#qR;yJgQX
zaU7JGml_9bildk+jYrH!jYqI3uF{{kB%;qBv2V4w%si!cAx1`yHPvHVV?1IC{?1r8
zR^hzr{xwhicuTQi?zBZ(T=L@KVn1KHTsA^X#zRbA8zBY<<^B&@-QO(B6s(rTj>d?w
zqL=rj7;!c6Z<)M0Ui_)o$hQ*2E@gBRIZfrfkz!G(7VRoL2_*&Rsk|vg{KF)ok6>jB
z#MmekURiojT@x0)JX`A?V(S-(c!^AxyBCNA??1Q>cuwf&*F|r2yu~<R9>rWwiuuG7
z$)d`{bYhyw^2@|nKB=@!T*N)D+awO-PZFmp#14qE@zk4$B}}exWY<k$vTY)3tQ5WV
zmnAsF(a;N4{-|jQ#)`#2thO+ArcyKzceZ@JQk($%KOx>X8f>rfw;KFUhz*~*0RI!x
zixsBrAvV|`rm!W|;%5FDr}MoPvpdz|EaJ}dfzK=#?<2Y#*1TLS@ID9o-U8V>%f)W*
zn=yKfA%_(`CytTdtP#&+oDg}_N>R&0ZTr*WG2kIKzh3+q@vX;z>nXzZWC35#t=0bZ
z_}1WC4_<l8z3a(;Ry2fo@MW~2c^Er(5n|X+pB3l&7~#EXS2{B4@*3uoXZ?(V9SvC0
z`55_(goepj6JVtAGLoy;h(E+<1R}q_Ry5FWXDjCrGa1+ijp8_NtMDc<TQSoZw!BG<
z_fjgh+SDX=-D|7$<Uj&*JtyM1pUMo+i?_dp{QUL!PuP36$-wU4;FDjxK_&lJ8+`I@
z_@0CBw(Q&nF@x}0V1wwotA~7fBSsfL3vd5S{E}zHTR#_H=iAn`S$rWF!!DnRJMqRB
z%&u$`?_mGRi{ekXmzM4j<9LRzd0G5|_m|qlX+gxS+0gllh~FUm2IDtG?tCS5)Nk3f
zDoq&wV_@#(nsELr9zxlQYE1$VX06mDw=P41)zzB#AVG)_1a^FxW+Z!Kg(j3uS+0p^
z<0~~fJ~f)TmuaHd;4)2aYqdsXwrWkZ_lL0#=g(Y*^gB4G+A5SXSgp~r$161v>|hN}
z*Hvmp1%PlSF4JT%Z6(tAr-d@p)7ntBc{yiXg|fykM+W(IDDdyqnu%;?6|$;cg=6zp
zqKsUQnz$C#mH4Z3CH|>ihRULFq^m>*Ug5eb1X?OJ!R(`95z(xNFJ<o2+HiKgQd7sq
zS0OO32KjY!y49S)Mr43?F)!DA$ZA)h(JHx`J+%mJ=6`TGVXSABW(xaft!7j!e%Y&h
z{W`9eyG9vT(VA9i#<Rx}MOxn^7O?_{YU_|2=fR9<dS<KBlrY;0WP;{2u<Ny&RPO{7
zYG6B8AQ}D%=i=jib|_wnV=b#RiCij5;CkW0V_8`((uJ);fvYsL`SQY<Wu<01r_j;}
zfwEaOn#pV@SNiM<oc^6^%_Q0Qw5Ik3FzEus0b{e8wQ=wg^DNTFCA=i~KIKX~-B{%P
z^%9F*tb)x7ye$AvRl{`(><+*y)v%AHAn2z0ncLOye=4(00r-L%eoBFD0T`C3RI5<n
ze+J-8HT+`*o>b_UZC1l;6xb4gt!g-2fqMe*aW%YBfrW?t%=^?ZKHPgh(*v-6sY-KE
zfj0->S!x*L)%!UgfE(0si~>h|-!J<$H5{+Nj|X6n8lI=Xn*(s<Q!3R)De(CKJXH-Z
zRp9s^_+_tD!}w1w@5dB??P~aY3Tz9&7t}COV0Qq93YBW36<9aTFFR8Whbgcr0GrkD
z0>A74Y*oWpU3ouO1MqP*oT|WSkN9Qxso`h^t_Z;TWh%|*DsX!Mo~4Ep6!>ZYZcxJu
z{j#U~Wxu9|u~71UY6GxG4L_p52Lo_qrAoE=3fv!nr>fy31vWnFm%UOAQw6pJV7nU5
zSKyuid_fI|D6mlEXAV^=)rR?H2jEN&S1AjgROOrHUw;)dtKm=uu29-4W>v$NDt)uJ
z1>oaqxLtuy2jD(6yjp?#1F*hYrP_1_POJ6_sbaI#aJ&M~4Zsa*`06s>tc?NqH8p%#
zfe!~@j~d>nz*hrs<Z_j2a}_v#xnH%ZYB)`Srw8DbYPi3`H*0kOwyWXO3fvxmFR0;d
z3VbO5Lybzc3Iz_W@vD}ph9@cTqyTJI!=VaX5rC~~_|j88rrQGWaW&koz^4OnpBi4R
z!2JPOze1(?bOlaZ;n#eY8je@sxdFIA4PRaAo3$|jzov!{EAZg}>`}uT75HiZj;vLw
zHdle;YyGNCRl{itJUsxfRKxvCe6v;uV7nSVt-$R8_<|bVrofj1FsxLmR-wS5EB&fv
zs^LirJShO1)o`c+R|H_I8ospH$8=i&KCXt_75H=j?o-376}UeD>+4jSPgmfyI=|+#
z)Ns54&kev0b=q-|$zJ1BnMzvIV#}*5vvQ_pG7pFQlzetone0z*eJpYn!pD@p|E%=G
z$JkUgjP<_vGkuj$!((iv8n!6#Y6Z?=_Ep-)U@GfFDwyGIGM`m=A5=7%tn|~K_VLV7
z`hFF1*sQ0uagPotyf+s4$o#N>yj>ZuRoM8)Pb=damGNWjHO}ryW&Y3w`=?zUBF1kZ
zZeITJi$BI9pF#VrQu>D%-K*UyHWlG@ey$NS?uEbdF%!ls<9C$4N$LCXjYInFL;B~H
zzF$ti(pR)vC-@n~&-5wa?>|1IZyC}*IHZ4RNMHEjz5K=x>6^U$iTLQEtZbt~;J2TD
zynV>{R|0FU*CxS3%u%l$6FFR=?^islN%quhlfmqt-alk|U|cbTZHQOI7vH-Pe)>s6
z#*Z=cYTRBwJXe9Q`kiTmb+s11!|)p>TUQUi@dAux4Py8@7_$L_!es~=k)Ip9Wa9G2
zemqJ3LBWXnxKWcI&#tJMnUR&TNLae8ddV|Ormd=bHX~E%K2=&Y^GC(<UrI;({x|;(
D_gLjB

diff --git a/fcore/app-init.sml b/fcore/app-init.sml
index 4a1b4d9..25dde11 100644
--- a/fcore/app-init.sml
+++ b/fcore/app-init.sml
@@ -47,6 +47,7 @@ struct
       , g = 0
       , b = 0
       , a = 1
+      , layer = 0
       , modalNum = 0
       , undo = []
       , redo = []
diff --git a/fcore/app-type.sml b/fcore/app-type.sml
index 69111df..385e7b0 100644
--- a/fcore/app-type.sml
+++ b/fcore/app-type.sml
@@ -33,6 +33,7 @@ struct
     , g: int
     , b: int
     , a: int
+    , layer: int
     , modalNum: int
     , undo: square list
     , redo: square list
diff --git a/fcore/app-with.sml b/fcore/app-with.sml
index 94d0942..b6d1399 100644
--- a/fcore/app-with.sml
+++ b/fcore/app-with.sml
@@ -51,6 +51,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -80,6 +81,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -110,6 +112,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -139,6 +142,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -169,6 +173,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -195,6 +200,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -225,6 +231,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -251,6 +258,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -281,6 +289,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -307,6 +316,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -337,6 +347,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -367,6 +378,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -397,6 +409,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -423,6 +436,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -453,6 +467,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -479,6 +494,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -509,6 +525,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -535,6 +552,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -565,6 +583,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -591,6 +610,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -621,6 +641,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -647,6 +668,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = modalNum
       , undo = undo
       , redo = redo
@@ -677,6 +699,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum = prevNum
         , undo
         , redo
@@ -705,6 +728,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = newNum
       , undo = undo
       , redo = redo
@@ -735,6 +759,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -763,6 +788,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -793,6 +819,7 @@ struct
         , g = _
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -821,6 +848,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -851,6 +879,7 @@ struct
         , g
         , b = _
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -879,6 +908,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -909,6 +939,7 @@ struct
         , g
         , b
         , a = _
+        , layer
         , modalNum
         , undo
         , redo
@@ -937,12 +968,73 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
       }
     end
 
+  fun layer (app: app_type) : app_type =
+    let
+      val
+        { mode
+        , mouseX
+        , mouseY
+        , xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , squares
+        , arrowX
+        , arrowY
+        , canvasWidth
+        , canvasHeight
+
+        , showGraph
+        , openFilePath
+        , fileBrowser
+        , fileBrowserIdx
+        , r
+        , g
+        , b
+        , a
+        , layer = _
+        , modalNum
+        , undo
+        , redo
+        } = app
+
+      val layer = modalNum
+    in
+      { mode = mode
+      , mouseX = mouseX
+      , mouseY = mouseY
+      , squares = squares
+      , arrowX = arrowX
+      , arrowY = arrowY
+      , canvasWidth = canvasWidth
+      , canvasHeight = canvasHeight
+      , windowWidth = windowWidth
+      , windowHeight = windowHeight
+      , xClickPoints = xClickPoints
+      , yClickPoints = yClickPoints
+
+      , showGraph = showGraph
+      , openFilePath = openFilePath
+      , fileBrowser = fileBrowser
+      , fileBrowserIdx = fileBrowserIdx
+      , r = r
+      , g = g
+      , b = b
+      , a = a
+      , layer = layer
+      , modalNum = modalNum
+      , undo = undo
+      , redo = redo
+      }
+    end
+
   fun canvasWidth (app: app_type, newCanvasWidth) =
     let
       val
@@ -967,6 +1059,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -999,6 +1092,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -1029,6 +1123,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -1061,6 +1156,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -1091,6 +1187,7 @@ struct
         , g
         , b
         , a
+        , layer
         , modalNum
         , undo
         , redo
@@ -1123,6 +1220,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
@@ -1153,6 +1251,7 @@ struct
         , g = _
         , b = _
         , a = _
+        , layer
         , modalNum
         , undo
         , redo
@@ -1179,6 +1278,7 @@ struct
       , g = g
       , b = b
       , a = a
+      , layer = layer
       , modalNum = 0
       , undo = undo
       , redo = redo
diff --git a/fcore/layer-tree.sml b/fcore/layer-tree.sml
index db87c01..0506e45 100644
--- a/fcore/layer-tree.sml
+++ b/fcore/layer-tree.sml
@@ -1,16 +1,19 @@
 structure LayerTree =
 struct
   type square = {r: int, g: int, b: int, a: int}
-  val emptyPixel = {r = 0, g = 0, b = 0, a = 0}
 
   type grid = square vector vector
 
-  fun isBlank ({a, ...}: square) = a = 0
-
   datatype tree =
     NODE of {key: int, value: grid, left: tree, right: tree}
   | LEAF
 
+  val emptyPixel = {r = 0, g = 0, b = 0, a = 0}
+
+  val emptyTree = LEAF
+
+  fun isBlank ({a, ...}: square) = a = 0
+
   fun insert (newKey, newValue, tree) =
     case tree of
       LEAF => NODE {key = newKey, value = newValue, left = LEAF, right = LEAF}