From 49b3f566b141ea71d39bab30d78079d5bb15a072 Mon Sep 17 00:00:00 2001
From: Rangi <sylvie.oukaour+rangi42@gmail.com>
Date: Sun, 13 Sep 2026 16:09:49 -0400
Subject: [PATCH] Fix handling of PNG files with RGB or RGBA color type that
 have a PLTE chunk

---
 src/gfx/pal_sorting.cpp         |   8 +++++++-
 test/gfx/rgb_with_plte.out.2bpp | Bin 0 -> 16 bytes
 test/gfx/rgb_with_plte.out.pal  | Bin 0 -> 8 bytes
 test/gfx/rgb_with_plte.png      | Bin 0 -> 99 bytes
 4 files changed, 7 insertions(+), 1 deletion(-)
 create mode 100644 test/gfx/rgb_with_plte.out.2bpp
 create mode 100644 test/gfx/rgb_with_plte.out.pal
 create mode 100644 test/gfx/rgb_with_plte.png

diff --git a/src/gfx/pal_sorting.cpp b/src/gfx/pal_sorting.cpp
index 56712fd9..45918340 100644
--- a/src/gfx/pal_sorting.cpp
+++ b/src/gfx/pal_sorting.cpp
@@ -33,7 +33,13 @@ void sortIndexed(std::vector<Palette> &palettes, std::vector<Rgba> const &embPal
 					return true;
 				}
 			}
-			unreachable_(); // LCOV_EXCL_LINE
+			// A PNG image using PNG_COLOR_TYPE_RGB (2) or PNG_COLOR_TYPE_RGBA (6) can still
+			// contain a PLTE chunk. From the PNG spec: "If present, it provides a suggested set of
+			// from 1 to 256 colors to which the truecolor image can be quantized if the viewer
+			// cannot display truecolor directly." This means that an input image may have pixels
+			// with colors that are not in the PLTE chunk, so iterating through `embPal` may finish
+			// without returning. In that case, we compare `lhs` and `rhs` directly.
+			return lhs < rhs;
 		});
 	}
 }
diff --git a/test/gfx/rgb_with_plte.out.2bpp b/test/gfx/rgb_with_plte.out.2bpp
new file mode 100644
index 0000000000000000000000000000000000000000..147b4e9a89dc9952bee4dcaed4ce42bafe673e8c
GIT binary patch
literal 16
NcmWG#Sj7;EgaIO$1N{I1

literal 0
HcmV?d00001

diff --git a/test/gfx/rgb_with_plte.out.pal b/test/gfx/rgb_with_plte.out.pal
new file mode 100644
index 0000000000000000000000000000000000000000..98c4fa004b03f7cf8041064c99cf1891a15cdeaf
GIT binary patch
literal 8
Ncmb1Vc)<K02mla81pfd4

literal 0
HcmV?d00001

diff --git a/test/gfx/rgb_with_plte.png b/test/gfx/rgb_with_plte.png
new file mode 100644
index 0000000000000000000000000000000000000000..7b218580f3a602fd997901bb410f597e722239df
GIT binary patch
literal 99
zcmeAS@N?(olHy`uVBq!ia0vp^93afW1SGw4HSYi^wg8_H*Z=?j1DT<RF4qAm2~QWt
ukcwN$Kh7UG@L@jV<Rf}r{&^0i3=Ev|_6J`bWuFaH!{F)a=d#Wzp$P!A&K(B;

literal 0
HcmV?d00001