From 5b866b643be559c41662f5e67ee4fecbbcc1f2f8 Mon Sep 17 00:00:00 2001
From: nothingTVatYT <rjakob13@googlemail.com>
Date: Sun, 8 Oct 2023 22:05:53 +0200
Subject: [PATCH] fix GetDesktopSize for Linux

---
 .../Engine/Platform/Linux/LinuxPlatform.cpp   | 38 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/Source/Engine/Platform/Linux/LinuxPlatform.cpp b/Source/Engine/Platform/Linux/LinuxPlatform.cpp
index af2c02ca6..4787b4549 100644
--- a/Source/Engine/Platform/Linux/LinuxPlatform.cpp
+++ b/Source/Engine/Platform/Linux/LinuxPlatform.cpp
@@ -2700,6 +2700,8 @@ Float2 LinuxPlatform::GetDesktopSize()
 	if (screenIdx >= count)
 		return Float2::Zero;
 
+    // this function is used as a fallback to place a window at the center of
+    // a screen so we report only one screen instead of the real desktop
 	Float2 size((float)xsi[screenIdx].width, (float)xsi[screenIdx].height);
 	X11::XFree(xsi);
 	return size;
@@ -2739,8 +2741,40 @@ Rectangle LinuxPlatform::GetMonitorBounds(const Float2& screenPos)
 
 Rectangle LinuxPlatform::GetVirtualDesktopBounds()
 {
-	// TODO: do it in a proper way
-	return Rectangle(Float2::Zero, GetDesktopSize());
+    if (!xDisplay)
+        return Rectangle::Empty;
+
+    int event, err;
+    const bool ok = X11::XineramaQueryExtension(xDisplay, &event, &err);
+    if (!ok)
+        return Rectangle::Empty;
+
+    int count;
+    X11::XineramaScreenInfo* xsi = X11::XineramaQueryScreens(xDisplay, &count);
+    if (count <= 0)
+        return Rectangle::Empty;
+    // get all screen dimensions and assume the monitors form a rectangle
+    // as you can arrange monitors to your liking this is not necessarily the case
+    int minX = INT32_MAX, minY = INT32_MAX;
+    int maxX = 0, maxY = 0;
+    for (int i = 0; i < count; i++)
+    {
+        int maxScreenX = xsi[i].x_org + xsi[i].width;
+        int maxScreenY = xsi[i].y_org + xsi[i].height;
+        if (maxScreenX > maxX)
+            maxX = maxScreenX;
+        if (maxScreenY > maxY)
+            maxY = maxScreenY;
+        if (minX > xsi[i].x_org)
+            minX = xsi[i].x_org;
+        if (minY > xsi[i].y_org)
+            minY = xsi[i].y_org;
+    }
+
+    Float2 org(static_cast<float>(minX), static_cast<float>(minY));
+    Float2 size(static_cast<float>(maxX - minX), static_cast<float>(maxY - minY));
+    X11::XFree(xsi);
+    return Rectangle(org, size);
 }
 
 String LinuxPlatform::GetMainDirectory()