From 2e9d2c4c5694accc9a40edfaabe5cb475e831aa2 Mon Sep 17 00:00:00 2001
From: Amartya Parijat <amartya.parijat@yatta.de>
Date: Mon, 14 Apr 2025 16:45:10 +0200
Subject: [PATCH] [Win32] Adjust tooltip to fit in one monitor #557

This commit contributes to fixing the infinite looping effect on
painting a tooltip over a TreeItem on win32 when a tooltip spans
over two monitors having more area on the other monitor than the one
on which the cursor is placed. The fix makes sure that the tooltip
is not drawn on the other monitors by shifting or adjusting the width.

Fixes https://github.com/eclipse-platform/eclipse.platform.swt/issues/557
---
 .../win32/org/eclipse/swt/widgets/Tree.java   | 58 ++++++++++++++++++-
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Tree.java b/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Tree.java
index d85ed201706..6e7d8001a0f 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Tree.java	
+++ b/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Tree.java	
@@ -8157,11 +8157,24 @@ LRESULT wmNotifyToolTip (NMHDR hdr, long wParam, long lParam) {
 			if (findCell (pt.x, pt.y, item, index, cellRect, itemRect)) {
 				RECT toolRect = toolTipRect (itemRect [0]);
 				OS.MapWindowPoints (handle, 0, toolRect, 2);
-				int width = toolRect.right - toolRect.left;
-				int height = toolRect.bottom - toolRect.top;
 				int flags = OS.SWP_NOACTIVATE | OS.SWP_NOZORDER | OS.SWP_NOSIZE;
 				if (isCustomToolTip ()) flags &= ~OS.SWP_NOSIZE;
-				OS.SetWindowPos (itemToolTipHandle, 0, toolRect.left, toolRect.top, width, height, flags);
+				// Retrieve the monitor containing the cursor position, as tool tip placement
+				// must occur on the same monitor to avoid potential infinite loops. When a tool tip
+				// appears on a different monitor than the cursor, the operating system may
+				// attempt to re-scale it based on that monitor's settings. This re-scaling
+				// triggers additional display messages to SWT, creating an infinite loop
+				// of positioning and re-scaling events.
+				// Refer: https://github.com/eclipse-platform/eclipse.platform.swt/issues/557
+				Point cursorLocation = display.getCursorLocation();
+				Rectangle monitorBounds = cursorLocation instanceof MonitorAwarePoint monitorAwarePoint
+						? getContainingMonitorBoundsInMultiZoomCoordinateSystem(monitorAwarePoint)
+						: getContainingMonitorBoundsInSingleZoomCoordinateSystem(cursorLocation);
+				if (monitorBounds == null) {
+					return null;
+				}
+				Rectangle adjustedTooltipBounds = fitTooltipBoundsIntoMonitor(toolRect, monitorBounds);
+				OS.SetWindowPos (itemToolTipHandle, 0, adjustedTooltipBounds.x, adjustedTooltipBounds.y, adjustedTooltipBounds.width, adjustedTooltipBounds.height, flags);
 				return LRESULT.ONE;
 			}
 			return result;
@@ -8170,6 +8183,45 @@ LRESULT wmNotifyToolTip (NMHDR hdr, long wParam, long lParam) {
 	return null;
 }
 
+/**
+ * Adjust the tool tip to fit in a single monitor either by shifting its position or by adjusting it's width.
+ */
+private Rectangle fitTooltipBoundsIntoMonitor(RECT tooltipBounds, Rectangle monitorBounds) {
+	int tooltipWidth = tooltipBounds.right - tooltipBounds.left;
+	int tooltipHeight = tooltipBounds.bottom - tooltipBounds.top;
+	if (tooltipBounds.left < monitorBounds.x) {
+		tooltipBounds.left = monitorBounds.x;
+	}
+	int monitorBoundsRightEnd = monitorBounds.x + monitorBounds.width;
+	if (tooltipBounds.right > monitorBoundsRightEnd) {
+		if (tooltipWidth <= monitorBounds.width) {
+			tooltipBounds.left = monitorBoundsRightEnd - tooltipWidth;
+		} else {
+			tooltipBounds.left = monitorBounds.x;
+		}
+		tooltipWidth = monitorBoundsRightEnd - tooltipBounds.left;
+	}
+	return new Rectangle(tooltipBounds.left, tooltipBounds.top, tooltipWidth, tooltipHeight);
+}
+
+private Rectangle getContainingMonitorBoundsInSingleZoomCoordinateSystem(Point point) {
+	int zoom = getZoom();
+	point = DPIUtil.scaleUp(point, zoom);
+	for (Monitor monitor : display.getMonitors()) {
+		Rectangle monitorBounds = DPIUtil.scaleUp(monitor.getBounds(), zoom);
+		if (monitorBounds.contains(point)) {
+			return monitorBounds;
+		}
+	}
+	return null;
+}
+
+private Rectangle getContainingMonitorBoundsInMultiZoomCoordinateSystem(MonitorAwarePoint point) {
+	Monitor monitor = point.getMonitor();
+	return new Rectangle(monitor.x, monitor.y, DPIUtil.scaleUp(monitor.width, monitor.zoom),
+			DPIUtil.scaleUp(monitor.height, monitor.zoom));
+}
+
 LRESULT wmNotifyToolTip (NMTTCUSTOMDRAW nmcd, long lParam) {
 	switch (nmcd.dwDrawStage) {
 		case OS.CDDS_PREPAINT: {