From b841473a0bd4a1a74a0b64f1ec2ab199035c349f Mon Sep 17 00:00:00 2001
From: Vaxry <vaxry@vaxry.net>
Date: Sun, 6 Jul 2025 15:22:25 +0200
Subject: [PATCH] png: libpng is straight alpha, but cairo is premult

ref #23
---
 src/image/formats/Png.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/image/formats/Png.cpp b/src/image/formats/Png.cpp
index e31cdd8..914d797 100644
--- a/src/image/formats/Png.cpp
+++ b/src/image/formats/Png.cpp
@@ -111,6 +111,10 @@ static std::expected<cairo_surface_t*, std::string> loadPNG(png_structp png, png
         uint8_t g               = rawData[i + 1];
         uint8_t b               = rawData[i + 2];
         uint8_t a               = rawData[i + 3];
+
+        r *= ((float)a) / 255.F;
+        g *= ((float)a) / 255.F;
+        b *= ((float)a) / 255.F;
         *(uint32_t*)&rawData[i] = (a << 24) | (r << 16) | (g << 8) | b;
     }