From 8733ba27340d93ccd1193f34aade5ac907adbd24 Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis@chromium.org>
Date: Wed, 6 Dec 2023 08:37:51 -0500
Subject: [PATCH] LibPDF: Fix decoding of IndexedColorSpace for palette sizes
 != 255

Previously, we were scaling palette indices from 0..(palette_size - 1)
to 0..255 before using them as index into the palette. Instead, do not
scale palette indices before using them as indices.

(Renderer::load_image() uses `component_value_decoders.empend(
.0f, 255.0f, dmin, dmax)`, so to get an identity mapping, we have to
return `0, 255` from IndexedColorSpace::default_decode()).

Fixes rendering of the gradient on page 5 of 0000277.pdf.
---
 Userland/Libraries/LibPDF/ColorSpace.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Userland/Libraries/LibPDF/ColorSpace.cpp b/Userland/Libraries/LibPDF/ColorSpace.cpp
index 766ecb25a1..8af8ae1716 100644
--- a/Userland/Libraries/LibPDF/ColorSpace.cpp
+++ b/Userland/Libraries/LibPDF/ColorSpace.cpp
@@ -701,7 +701,7 @@ PDFErrorOr<Color> IndexedColorSpace::color(ReadonlySpan<Value> arguments) const
 
 Vector<float> IndexedColorSpace::default_decode() const
 {
-    return { 0.0, static_cast<float>(m_hival) };
+    return { 0.0, 255.0 };
 }
 
 PDFErrorOr<NonnullRefPtr<SeparationColorSpace>> SeparationColorSpace::create(Document* document, Vector<Value>&& parameters)