From 3ca5d4ab298c5ce5ff24b79c1a84d2a0fc1ea572 Mon Sep 17 00:00:00 2001
From: ispyisail <shane.ringrose@gmail.com>
Date: Mon, 31 Aug 2026 05:45:35 +1200
Subject: [PATCH] Fix GitHub issue #798: element editor crash on scroll-wheel
 zoom

ElementView applied scale() on every wheel notch with no bound on the
resulting view transform. Held down, the scroll-wheel zoom drives the
transform scale (m11) to floating-point overflow; the transform becomes
non-invertible, mapToScene() returns NaN and the next background paint
aborts the editor ("program closes completely" as reported on Windows).

Route zoomIn/zoomOut/zoomInSlowly/zoomOutSlowly through a new
scaleClamped() helper that only applies the scale while the result stays
within [m_min_zoom, m_max_zoom] (0.1 .. 200). Behaviour within that range
is unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HdWpDp3TrPKbHnv7YUcNJj
---
 sources/editor/elementview.cpp | 25 +++++++++++++++++++++----
 sources/editor/elementview.h   |  7 +++++++
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/sources/editor/elementview.cpp b/sources/editor/elementview.cpp
index 62226f748..b1f4e30ec 100644
--- a/sources/editor/elementview.cpp
+++ b/sources/editor/elementview.cpp
@@ -100,13 +100,30 @@ void ElementView::setSelectionMode()
 	emit(modeChanged());
 }
 
+/**
+	Applique un facteur d'echelle a la vue en bornant l'echelle resultante
+	entre m_min_zoom et m_max_zoom. Sans cette borne, un zoom repete (molette)
+	finit par faire deborder la transformation de la vue et fait planter
+	l'editeur (issue #798).
+	@param factor facteur d'echelle a appliquer
+*/
+void ElementView::scaleClamped(qreal factor)
+{
+	const qreal current = transform().m11();
+	const qreal target = current * factor;
+	if (target < m_min_zoom || target > m_max_zoom) {
+		return;
+	}
+	scale(factor, factor);
+}
+
 /**
 	Agrandit le schema (+33% = inverse des -25 % de zoomMoins())
 */
 void ElementView::zoomIn()
 {
 	adjustSceneRect();
-	scale(4.0/3.0, 4.0/3.0);
+	scaleClamped(4.0/3.0);
 }
 
 /**
@@ -115,7 +132,7 @@ void ElementView::zoomIn()
 void ElementView::zoomOut()
 {
 	adjustSceneRect();
-	scale(0.75, 0.75);
+	scaleClamped(0.75);
 }
 
 /**
@@ -123,7 +140,7 @@ void ElementView::zoomOut()
 */
 void ElementView::zoomInSlowly()
 {
-	scale(1.02, 1.02);
+	scaleClamped(1.02);
 }
 
 /**
@@ -131,7 +148,7 @@ void ElementView::zoomInSlowly()
 */
 void ElementView::zoomOutSlowly()
 {
-	scale(0.98, 0.98);
+	scaleClamped(0.98);
 }
 
 /**
diff --git a/sources/editor/elementview.h b/sources/editor/elementview.h
index 54e5dc49d..09168b996 100644
--- a/sources/editor/elementview.h
+++ b/sources/editor/elementview.h
@@ -53,6 +53,13 @@ class ElementView : public QGraphicsView {
 	
 	private:
 	QRectF applyMovement(const QRectF &, const QPointF &);
+	void scaleClamped(qreal factor);
+
+	/// Lowest and highest allowed value of the view transform scale (m11).
+	/// Prevents the wheel-zoom from driving the transform to overflow, which
+	/// crashes the editor (bugtracker / GitHub issue #798).
+	static constexpr qreal m_min_zoom = 0.1;
+	static constexpr qreal m_max_zoom = 200.0;
 	
 	public slots:
 	void setVisualisationMode();