From 81bd7b1f5f6a63e5dcc68846c1695a64dc32d5f6 Mon Sep 17 00:00:00 2001
From: Danilo Aimini <82231674+AMZN-daimini@users.noreply.github.com>
Date: Tue, 14 Sep 2021 20:11:00 -0700
Subject: [PATCH] Implement a system that resizes the ghost widget
 appropriately to avoid undefined behavior due to it being moved into the gap
 between screens caused by scaling.

Signed-off-by: Danilo Aimini <82231674+AMZN-daimini@users.noreply.github.com>
---
 .../Components/FancyDocking.cpp               | 14 +++---
 .../Components/FancyDockingGhostWidget.cpp    | 50 ++++++++++++++++++-
 .../Components/FancyDockingGhostWidget.h      |  9 ++++
 3 files changed, 65 insertions(+), 8 deletions(-)

diff --git a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDocking.cpp b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDocking.cpp
index f60a98f392..7a76781cd7 100644
--- a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDocking.cpp
+++ b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDocking.cpp
@@ -1615,14 +1615,16 @@ namespace AzQtComponents
             }
 
             // Handle snapping to the screen edges/other floating windows while dragging
-            QScreen* screen = Utilities::ScreenAtPoint(globalPos);
+            QScreen* screen = QApplication::screenAt(globalPos);
 
-            AdjustForSnapping(placeholder, screen);
+            if (screen)
+            {
+                AdjustForSnapping(placeholder, screen);
+                m_state.setPlaceholder(placeholder, screen);
 
-            m_state.setPlaceholder(placeholder, screen);
-
-            m_ghostWidget->Enable();
-            RepaintFloatingIndicators();
+                m_ghostWidget->Enable();
+                RepaintFloatingIndicators();
+            }
         }
 
         return m_dropZoneState.dragging();
diff --git a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.cpp b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.cpp
index 6894e5b011..04387875df 100644
--- a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.cpp
+++ b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.cpp
@@ -8,6 +8,7 @@
 
 #include <AzQtComponents/Components/FancyDockingGhostWidget.h>
 
+#include <QApplication>
 #include <QDebug>
 #include <QCloseEvent>
 #include <QScreen>
@@ -76,7 +77,32 @@ namespace AzQtComponents
             window->setScreen(screen);
         }
 
-        setGeometry(targetRect);
+        QPoint midPoint = targetRect.topLeft() + QPoint(targetRect.width() / 2, targetRect.height() / 2);
+        QScreen* pointScreen = QApplication::screenAt(midPoint);
+        QRect rect(targetRect);
+
+        if (!pointScreen || pointScreen != screen)
+        {
+            if (midPoint.x() >= QCursor::pos().x())
+            {
+                rect.setLeft(rect.left() - rect.width());
+                rect.setTop(rect.top() - rect.height());
+                m_paintMode = PaintMode::BOTTOMRIGHT;
+            }
+            else
+            {
+                rect.setRight(rect.right() + rect.width());
+                rect.setTop(rect.top() - rect.height());
+                m_paintMode = PaintMode::BOTTOMLEFT;
+            }
+        }
+        else
+        {
+            m_paintMode = PaintMode::FULL;
+        }
+
+        setGeometry(rect);
+
         setPixmapVisible(true);
         if (needsRepaint)
         {
@@ -135,7 +161,27 @@ namespace AzQtComponents
                 yOffset = widgetSize.height() - aspectRatioHeight;
             }
 
-            painter.drawPixmap(QRect(0, yOffset, widgetSize.width(), aspectRatioHeight), m_pixmap);
+            switch (m_paintMode)
+            {
+                case PaintMode::FULL:
+                    {
+                        painter.drawPixmap(QRect(0, yOffset, widgetSize.width(), aspectRatioHeight), m_pixmap);
+                    }
+                break;
+
+                case PaintMode::BOTTOMLEFT:
+                    {
+                        painter.drawPixmap(QRect(0, (widgetSize.height() + yOffset) / 2, widgetSize.width() / 2, aspectRatioHeight / 2), m_pixmap);
+                    }
+                break;
+
+                case PaintMode::BOTTOMRIGHT:
+                    {
+                        painter.drawPixmap(QRect(widgetSize.width() / 2, (widgetSize.height() + yOffset) / 2, widgetSize.width() / 2, aspectRatioHeight / 2), m_pixmap);
+                    }
+                break;
+            }
+
             if (m_clipToWidgets)
             {
                 painter.restore();
diff --git a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.h b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.h
index cadcbd9c8a..6649c6d848 100644
--- a/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.h
+++ b/Code/Framework/AzQtComponents/AzQtComponents/Components/FancyDockingGhostWidget.h
@@ -45,5 +45,14 @@ namespace AzQtComponents
         QPixmap m_pixmap;
         bool m_visible = false; // maintain our own flag, so that we're always ready to render ignoring Qt's widget caching system
         bool m_clipToWidgets = false;
+
+        enum class PaintMode
+        {
+            FULL = 0,
+            BOTTOMLEFT,
+            BOTTOMRIGHT
+        };
+
+        PaintMode m_paintMode = PaintMode::FULL;
     };
 } // namespace AzQtComponents