From 23033e2050d9ef099ecb02dde0f56f9f23e8d30d Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Fri, 4 Mar 2022 23:17:07 +0000
Subject: [PATCH] Prevent double unpremultiply with some composite blends

---
 docs/changelog.md                               |   5 +++++
 src/pipeline.cc                                 |   2 +-
 test/fixtures/expected/composite-multiple.png   | Bin 320 -> 320 bytes
 .../expected/composite.blend.dest-over.png      | Bin 291 -> 292 bytes
 test/fixtures/expected/composite.blend.over.png | Bin 292 -> 292 bytes
 .../expected/composite.blend.saturate.png       | Bin 288 -> 286 bytes
 test/fixtures/expected/composite.blend.xor.png  | Bin 286 -> 285 bytes
 test/unit/extend.js                             |   2 +-
 8 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/docs/changelog.md b/docs/changelog.md
index 58e80884..25dbe2cd 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -4,6 +4,11 @@
 
 Requires libvips v8.12.2
 
+### v0.30.3 - TBD
+
+* Prevent double unpremultiply with some composite blend modes (regression in 0.30.2).
+  [#3118](https://github.com/lovell/sharp/issues/3118)
+
 ### v0.30.2 - 2nd March 2022
 
 * Improve performance and accuracy when compositing multiple images.
diff --git a/src/pipeline.cc b/src/pipeline.cc
index 2289dd21..a0858605 100644
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -354,7 +354,7 @@ class PipelineWorker : public Napi::AsyncWorker {
       }
 
       bool const shouldPremultiplyAlpha = sharp::HasAlpha(image) &&
-        (shouldResize || shouldBlur || shouldConv || shouldSharpen || shouldComposite);
+        (shouldResize || shouldBlur || shouldConv || shouldSharpen);
 
       // Premultiply image alpha channel before all transformations to avoid
       // dark fringing around bright pixels
diff --git a/test/fixtures/expected/composite-multiple.png b/test/fixtures/expected/composite-multiple.png
index 2aef0fbdee9faa6bb1fd6002bb265361800e4461..18671a39b6ce4491c6ec64bd0c852074559e5f21 100644
GIT binary patch
delta 255
zcmV<b0095M0>A>0Nq@}13_t)CLt&JJp*$#WAXY7X+I^V7$!Q!*<%Y3S#mYYk0WJZS
z4qWY{=m;agbi2tVf&kO)C}Ru)%#&o0Mu5?Q^pBz=i~!T^CYJ~TOt+(qF$geEl0lj;
z0oEcr^_uT%r@9>`Km?d>mpQ@+Fx^gbi6Fq7C}Ru)j1HUz>3DdFc*?~kf?N2qOqjMY
z)>#;&<0UdJR4*H8EB*YuOsLJ;{S9Nc1c(5K4qT3Kd;<?y808W{fZdKOV+;c9c3l~y
z5#TAh4>;F6<q+WLcA8}Z0vz3Lv(7?*<1|^QBEZq<zz^-%sPaUg)93&I002ovPDHLk
FV1h4PZ`c3;

delta 255
zcmV<b0095M0>A>0Nq@w^1ji5+O=%d)lS<?b#HyuFyAKmMIgMkf+%R^kSotR*z$L)a
zfvbHK9bp8RZa29^5Ma6;WsE_9d6Ep$2rxR3{!w&<5n#IA<Pt%E>2{Pc1_9<tGD!0!
zz*=OdUh{qJRJX$fhyc^=GDjEzrrT*Q5d@eMWsE_9(Sg$-9e6JhPr0~6a0_3S3DY*l
zItznzyhNsj>SZHsrJtXd3AI_fzhUf_01@EOfy)t&Z{Pt7qg)~gu-kEEj6s0it}BBy
z0z5_c0q2^h90DBOPP0rvfTP=O)>#N}oF)rZ1UNb!_yJla9Ple{DG~qx002ovPDHLk
FV1iKQYTf_<

diff --git a/test/fixtures/expected/composite.blend.dest-over.png b/test/fixtures/expected/composite.blend.dest-over.png
index a230c331a763b265a97d97b243ad8aadded7a8ce..f7f7b1eb92d5a9b910e864e6104e642e80264fa9 100644
GIT binary patch
delta 170
zcmV;b09F5^0;B?vIZxI}L_t(|ob8)25yUVM#01iS4o^rdGzY_fij5~Kj(|oQZ(}x$
z$KMPP9*+bPAOf6bMH+|zM*}%`379Yf91Y|H316&y>9zou051((^^u@VP-wykFm0QB
zL=a%wMmb{;U`{%RGy;qU(ogX<33~`|``M7!m0-dMa5Rv9iYANzr)`su2m+k8QNPZZ
Y8`#oRLlzl`^#A|>07*qoM6N<$g0{&&X8-^I

delta 193
zcmZ3&w3umvW&Kr87srr_Id5lg<UL{_aM)tg=7YJ*F3yqs7p&nHafgY8bG4!LvB&vr
z9R2Q0oC1t~o0WK78WuOs+0Ei3!Pv+4sj)>rY+p%qgLlJpwsloqYCQ~>x1DrnVO*9w
z#h8up*^*)p<pUWCe?@#HfI^e|IhcHIYozlqo$-7=!L8w<!^8z9=09e&*s|>Sn{(o|
smq8+ng_MWAtFT)G#2CNZE8^47@NUp{3F*1Wmd5}Dp00i_>zopr0G#<uVgLXD

diff --git a/test/fixtures/expected/composite.blend.over.png b/test/fixtures/expected/composite.blend.over.png
index 142e75ecbf3472b724ba9937bbd9a1a96c61d09c..8c58c402cd2abce69ec6d6db8562d48528d836fe 100644
GIT binary patch
delta 38
scmZ3&w1jDbC%aJtU%#i0$;5yIBHceioH^Cz?_dA|Pgg&ebxsLQ0Q7(iYybcN

delta 38
tcmZ3&w1jDbC%g8CzMDmcf)fJ{h#Yi_y0oxz(jEpN@O1TaS?83{1OO+X4y6D9

diff --git a/test/fixtures/expected/composite.blend.saturate.png b/test/fixtures/expected/composite.blend.saturate.png
index 86090025ab3f476f480d1fdd3218de83263e8a25..6c77b7fd2f2451f8a93042a2659c31c7597bb790 100644
GIT binary patch
literal 286
zcmeAS@N?(olHy`uVBq!ia0vp^0YGfS!3HEhs@wJeDb50q$YKTt<`*E$xV1Vc8z^|e
z)5S5QV$R#y8+i{H@EraT8Ta}5E8bl8s~YU~4ih@22}txG=Mj)w&myG2G$+kfs)NCu
z`Q~mG9|^`jwolD1?UU_eSt?j8q$*x%&N5)~xveHI$TDMF;5iAF8NSaaxHVjK_(e^L
zI<-W8#$)H(YSys`yEQCs{1R-E$YPN@yT(P}!Is`#*2#KmZn2APpX!MM{l?(w>gTe~
HDWM4f7$9S=

literal 288
zcmeAS@N?(olHy`uVBq!ia0vp^0YGfS!3HEhs@wJeDb50q$YKTt<`*E$xV1Vc8z^|m
z)5S5QV$R#y8wHOT@EqPS(|DFydfJKlgD;w#xF0kaOAAZ%&zDrN`6uMjz)>(uG*f{|
zhBxKCkU=7gh13alp?wxVFS$0jH%w=nSJkD~!*F@qNp}{;Ww}#~*%;F<TP_hyFqu$C
zO^NlMH=G+jZdP2ceXvFFL59L#5nl;LzuRi^f-Dxfi|3u2A+7Go+UkDxx)acM44$rj
JF6*2UngAyKWBC98

diff --git a/test/fixtures/expected/composite.blend.xor.png b/test/fixtures/expected/composite.blend.xor.png
index 755440458d809c50bd8acea0983146be516dbd0e..916eaf77635319b1db22abca15524ef31fc66ab8 100644
GIT binary patch
literal 285
zcmeAS@N?(olHy`uVBq!ia0vp^0YGfS!3HEhs@wJeDb50q$YKTt<`*E$xV1Vc8z^|*
z)5S5QV$R#y8+i{H@ErcJ^G{`!^KD1dQwRA4R2HeqNc11)5s+KYBBa1HC(Tu=gTbBo
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z7F(8zKRG9!dl@9MSV(!;y9&ECT;6ulorTfw_KMxc&zN>!{3F(L>2Wa7YYd*QelF{r
G5}E)3zG7kk

literal 286
zcmeAS@N?(olHy`uVBq!ia0vp^0YGfS!3HEhs@wJeDb50q$YKTt<`*E$xV1Vc8z^|e
z)5S5QV$R#y8+n->c@FQ`xo4-b^CYKy8*Y7v2^OZu4^{j*!|?FqbO$DvhRbU_m<1nX
zD3nic;8Z?v(IIZahYgjN*D{1REN+bUzt|#}aLepxhr)p^y+y|q4#Zfsn=tjTU81JM
zM?=nPj)K2ACmwqlB(hjYdDy!OyER<icG8`N(eL(({PZ*Is?J*vW+$pK0{zC|>FVdQ
I&MBb@0IctB$N&HU

diff --git a/test/unit/extend.js b/test/unit/extend.js
index 3d81e312..1e22df77 100644
--- a/test/unit/extend.js
+++ b/test/unit/extend.js
@@ -158,6 +158,6 @@ describe('Extend', function () {
       })
       .raw()
       .toBuffer();
-    assert.deepStrictEqual(Array.from(data), [191, 25, 65, 204, 238, 31, 82, 204]);
+    assert.deepStrictEqual(Array.from(data), [191, 25, 66, 204, 191, 25, 66, 204]);
   });
 });