From 325d67578667df0a95b17b86661c74c2a1dca8a8 Mon Sep 17 00:00:00 2001
From: David Capello <david@igarastudio.com>
Date: Thu, 28 Mar 2019 10:44:06 -0300
Subject: [PATCH] Fix thumbnails for indexed images with transparent color (GIF
 files mainly)

---
 src/app/thumbnail_generator.cpp | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/app/thumbnail_generator.cpp b/src/app/thumbnail_generator.cpp
index 50217e2cb..6118fb35d 100644
--- a/src/app/thumbnail_generator.cpp
+++ b/src/app/thumbnail_generator.cpp
@@ -105,6 +105,15 @@ private:
         // The palette to convert the Image
         palette.reset(new Palette(*sprite->palette(frame_t(0))));
 
+        // Special case for indexed images:
+        // If the sprite is transparent -> set the transparent color index alpha = 0
+        if (sprite->colorMode() == ColorMode::INDEXED &&
+            !sprite->backgroundLayer()) {
+          int i = sprite->transparentColor();
+          if (i >= 0 && i < int(palette->size()))
+            palette->setEntry(i, doc::rgba(0, 0, 0, 0));
+        }
+
         const int w = sprite->width()*sprite->pixelRatio().w;
         const int h = sprite->height()*sprite->pixelRatio().h;