From fc860a226e03e70dfe49fe691743a401cb4335c6 Mon Sep 17 00:00:00 2001
From: Lewis Lakerink <llakerink@swin.edu.au>
Date: Sat, 11 Sep 2021 08:58:18 +1000
Subject: [PATCH] Fix screen edge detection

---
 src/screenedge.cpp | 44 ++++++++++++++++++++++++--------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/src/screenedge.cpp b/src/screenedge.cpp
index 77f31d93e1..c971a146d6 100644
--- a/src/screenedge.cpp
+++ b/src/screenedge.cpp
@@ -914,20 +914,21 @@ static bool isLeftScreen(const QRect &screen, const QRect &fullArea)
     if (screen.x() == fullArea.x()) {
         return true;
     }
-    // the screen is also on the left in case of a vertical layout with a second screen
-    // more to the left. In that case no screen ends left of screen's x coord
+    // If any other screen has a right edge against our left edge, then this screen is not a left screen
     for (const AbstractOutput *output : outputs) {
         const QRect otherGeo = output->geometry();
         if (otherGeo == screen) {
             // that's our screen to test
             continue;
         }
-        if (otherGeo.x() + otherGeo.width() <= screen.x()) {
-            // other screen is completely in the left
+        if (screen.x() == otherGeo.x() + otherGeo.width()
+            && screen.y() < otherGeo.y() + otherGeo.height()
+            && screen.y() + screen.height() > otherGeo.y()) {
+            // There is a screen to the left
             return false;
         }
     }
-    // did not find a screen left of our current screen, so it is the left most
+    // No screen exists to the left, so this is a left screen
     return true;
 }
 
@@ -940,20 +941,21 @@ static bool isRightScreen(const QRect &screen, const QRect &fullArea)
     if (screen.x() + screen.width() == fullArea.x() + fullArea.width()) {
         return true;
     }
-    // the screen is also on the right in case of a vertical layout with a second screen
-    // more to the right. In that case no screen starts right of this screen
+    // If any other screen has any left edge against any of our right edge, then this screen is not a right screen
     for (const AbstractOutput *output : outputs) {
         const QRect otherGeo = output->geometry();
         if (otherGeo == screen) {
             // that's our screen to test
             continue;
         }
-        if (otherGeo.x() >= screen.x() + screen.width()) {
-            // other screen is completely in the right
+        if (screen.x() + screen.width() == otherGeo.x()
+            && screen.y() < otherGeo.y() + otherGeo.height()
+            && screen.y() + screen.height() > otherGeo.y()) {
+            // There is a screen to the right
             return false;
         }
     }
-    // did not find a screen right of our current screen, so it is the right most
+    // No screen exists to the right, so this is a right screen
     return true;
 }
 
@@ -966,20 +968,21 @@ static bool isTopScreen(const QRect &screen, const QRect &fullArea)
     if (screen.y() == fullArea.y()) {
         return true;
     }
-    // the screen is also top most in case of a horizontal layout with a second screen
-    // more to the top. In that case no screen ends above screen's y coord
+    // If any other screen has any bottom edge against any of our top edge, then this screen is not a top screen
     for (const AbstractOutput *output : outputs) {
         const QRect otherGeo = output->geometry();
         if (otherGeo == screen) {
             // that's our screen to test
             continue;
         }
-        if (otherGeo.y() + otherGeo.height() <= screen.y()) {
-            // other screen is completely above
+        if (screen.y() == otherGeo.y() + otherGeo.height()
+            && screen.x() < otherGeo.x() + otherGeo.width()
+            && screen.x() + screen.width() > otherGeo.x()) {
+            // There is a screen to the top
             return false;
         }
     }
-    // did not find a screen above our current screen, so it is the top most
+    // No screen exists to the top, so this is a top screen
     return true;
 }
 
@@ -992,20 +995,21 @@ static bool isBottomScreen(const QRect &screen, const QRect &fullArea)
     if (screen.y() + screen.height() == fullArea.y() + fullArea.height()) {
         return true;
     }
-    // the screen is also bottom most in case of a horizontal layout with a second screen
-    // more below. In that case no screen starts below screen's y coord + height
+    // If any other screen has any top edge against any of our bottom edge, then this screen is not a bottom screen
     for (const AbstractOutput *output : outputs) {
         const QRect otherGeo = output->geometry();
         if (otherGeo == screen) {
             // that's our screen to test
             continue;
         }
-        if (otherGeo.y() >= screen.y() + screen.height()) {
-            // other screen is completely below
+        if (screen.y() + screen.height() == otherGeo.y()
+            && screen.x() < otherGeo.x() + otherGeo.width()
+            && screen.x() + screen.width() > otherGeo.x()) {
+            // There is a screen to the bottom
             return false;
         }
     }
-    // did not find a screen below our current screen, so it is the bottom most
+    // No screen exists to the bottom, so this is a bottom screen
     return true;
 }