From 0af969543d1d898c071c82e15e003ba428ba1178 Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Tue, 8 Sep 2020 17:05:38 +0200
Subject: [PATCH] nitpicker: preserve alpha channel during resize

This patch reduces flickering artifacts that appear during the
resizing of clients that use an alpha channel.

Issue #3812
---
 .../os/src/server/nitpicker/resizeable_texture.h  | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/repos/os/src/server/nitpicker/resizeable_texture.h b/repos/os/src/server/nitpicker/resizeable_texture.h
index 2907f6c537..942d22a841 100644
--- a/repos/os/src/server/nitpicker/resizeable_texture.h
+++ b/repos/os/src/server/nitpicker/resizeable_texture.h
@@ -16,6 +16,7 @@
 
 /* Genode includes */
 #include <blit/painter.h>
+#include <os/pixel_alpha8.h>
 
 /* local includes */
 #include "chunky_texture.h"
@@ -80,6 +81,20 @@ class Nitpicker::Resizeable_texture
 				Texture<PT> const &texture = *_textures[_current];
 
 				Blit_painter::paint(surface, texture, Point(0, 0));
+
+				/* copy alpha channel */
+				if (_textures[_current]->alpha() && _textures[next]->alpha()) {
+
+					typedef Pixel_alpha8 AT;
+
+					Surface<AT> surface((AT *)_textures[next]->alpha(),
+					                    _textures[next]->Texture_base::size());
+
+					Texture<AT> const texture((AT *)_textures[_current]->alpha(), nullptr,
+					                          _textures[_current]->Texture_base::size());
+
+					Blit_painter::paint(surface, texture, Point(0, 0));
+				}
 			}
 
 			_textures[_current].destruct();