From 4145417f6748264dae27eac28cb53bd13ae18af5 Mon Sep 17 00:00:00 2001
From: Norman Feske <norman.feske@genode-labs.com>
Date: Tue, 27 Nov 2018 11:25:56 +0100
Subject: [PATCH] window_layouter: improve window-resize handling

This patch solves an off-by-one problem in the window-size calculation,
which resulted in sporadic artificial resize requests. In Sculpt, this
glitch caused flickering artifacts in VirtualBox windows caused by
superfluous guest desktop-resize handling.

Furthermore, the patch introduces the dropping of resize requests with
unchanged content.
---
 repos/gems/src/app/window_layouter/main.cc  | 17 +++-----
 repos/gems/src/app/window_layouter/window.h | 47 ++++++++++++++++++---
 2 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/repos/gems/src/app/window_layouter/main.cc b/repos/gems/src/app/window_layouter/main.cc
index 9cc35274e..6474c9c1b 100644
--- a/repos/gems/src/app/window_layouter/main.cc
+++ b/repos/gems/src/app/window_layouter/main.cc
@@ -362,26 +362,19 @@ void Window_layouter::Main::_gen_resize_request()
 {
 	bool resize_needed = false;
 	_window_list.for_each_window([&] (Window const &window) {
-		if (window.client_size() != window.requested_size())
+		if (window.resize_request_needed())
 			resize_needed = true; });
 
 	if (!resize_needed)
 		return;
 
 	_resize_request_reporter.generate([&] (Xml_generator &xml) {
-
 		_window_list.for_each_window([&] (Window const &window) {
+			window.gen_resize_request(xml); }); });
 
-			Area const requested_size = window.requested_size();
-			if (requested_size != window.client_size()) {
-				xml.node("window", [&] () {
-					xml.attribute("id",     window.id().value);
-					xml.attribute("width",  requested_size.w());
-					xml.attribute("height", requested_size.h());
-				});
-			}
-		});
-	});
+	/* prevent superfluous resize requests for the same size */
+	_window_list.for_each_window([&] (Window &window) {
+		window.resize_request_updated(); });
 }
 
 
diff --git a/repos/gems/src/app/window_layouter/window.h b/repos/gems/src/app/window_layouter/window.h
index 890d339c4..2d6c574fc 100644
--- a/repos/gems/src/app/window_layouter/window.h
+++ b/repos/gems/src/app/window_layouter/window.h
@@ -96,6 +96,14 @@ class Window_layouter::Window : public List_model<Window>::Element
 		 */
 		Area _requested_size;
 
+		/**
+		 * Most recent resize request propagated to the window manager
+		 *
+		 * Initially, no resize request must be generated because the
+		 * '_requested_size' corresponds to the window size.
+		 */
+		Area _reported_resize_request = _requested_size;
+
 		/**
 		 * Window may be partially transparent
 		 */
@@ -236,10 +244,10 @@ class Window_layouter::Window : public List_model<Window>::Element
 				return _drag_geometry;
 
 			/* resize window */
-			if (_drag_left_border)   x1 = x2 - _client_size.w();
-			if (_drag_right_border)  x2 = x1 + _client_size.w();
-			if (_drag_top_border)    y1 = y2 - _client_size.h();
-			if (_drag_bottom_border) y2 = y1 + _client_size.h();
+			if (_drag_left_border)   x1 = x2 - _client_size.w() + 1;
+			if (_drag_right_border)  x2 = x1 + _client_size.w() - 1;
+			if (_drag_top_border)    y1 = y2 - _client_size.h() + 1;
+			if (_drag_bottom_border) y2 = y1 + _client_size.h() - 1;
 
 			return Rect(Point(x1, y1), Point(x2, y2));
 		}
@@ -304,7 +312,35 @@ class Window_layouter::Window : public List_model<Window>::Element
 				xml.attribute("maximized", true);
 		}
 
-		Area requested_size() const { return _requested_size; }
+		/**
+		 * Return true if a request request to the window manager is due
+		 */
+		bool resize_request_needed() const
+		{
+			/* a resize request for the current size is already in flight */
+			if (_requested_size == _reported_resize_request)
+				return false;
+
+			return (_requested_size != _client_size);
+		}
+
+		/**
+		 * Mark the currently requested size as processed so that no further
+		 * resize requests for the same size are generated
+		 */
+		void resize_request_updated() { _reported_resize_request = _requested_size; }
+
+		void gen_resize_request(Xml_generator &xml) const
+		{
+			if (_requested_size == _client_size)
+				return;
+
+			xml.node("window", [&] () {
+				xml.attribute("id",     _id.value);
+				xml.attribute("width",  _requested_size.w());
+				xml.attribute("height", _requested_size.h());
+			});
+		}
 
 		void generate(Xml_generator &xml) const
 		{
@@ -372,6 +408,7 @@ class Window_layouter::Window : public List_model<Window>::Element
 			_drag_top_border    = false;
 			_drag_bottom_border = false;
 			_requested_size     = effective_inner_geometry().area();
+
 		}
 
 		void to_front_cnt(unsigned to_front_cnt) { _to_front_cnt = to_front_cnt; }