fix(editor): suppress spurious first-click element moves (#481)

When an item type is selected for the first time the properties dock
expands, causing the QGraphicsView viewport to shrink. Qt recalculates
scene coordinates and fires one or more synthetic mouseMoveEvents before
the user has actually moved the mouse.

The original code used a single-shot m_first_move flag in
CustomElementGraphicPart, which absorbed exactly one spurious event.
PartText and PartDynamicTextField had no protection at all.

Fix: compare screen-coordinate displacement against
QApplication::startDragDistance() (~4 px). Screen coordinates are
stable across viewport resizes, so the check correctly rejects
synthetic dock-expansion events while allowing genuine drags.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

sources/editor/graphicspart/customelementgraphicpart.cpp

@@ -20,6 +20,7 @@
 #include "../../QPropertyUndoCommand/qpropertyundocommand.h"
 #include "../elementscene.h"
 
+#include <QApplication>
 #include <QRegularExpression>
 
 /**
@@ -35,6 +36,7 @@ CustomElementGraphicPart::CustomElementGraphicPart(QETElementEditor *editor,
 	QGraphicsObject (parent),
 	CustomElementPart(editor),
 	m_hovered (false),
+	m_first_move (false),
 	_linestyle(NormalStyle),
 	_lineweight(NormalWeight),
 	_filling(NoneFilling),
@@ -1332,26 +1334,24 @@ void CustomElementGraphicPart::mousePressEvent(QGraphicsSceneMouseEvent *event)
 
 void CustomElementGraphicPart::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
 {
-		//m_first_move is used to avoid an unwanted behavior
-		//when the properties dock widget is displayed :
-		//1 there is no selection
-		//2 the dock widget width is set to minimum
-		//3 select a part, the dock widget gain new widgets used to edit
-		//the current selected part and the width of the dock grow
-		//so the width of the QGraphicsView is reduced and cause a mouse move event.
-		//When this case occur the part is moved but they should not. This bool fix it.
-	if (Q_UNLIKELY(m_first_move)) {
+	if (m_first_move) {
+		// Suppress spurious move events fired when the properties dock
+		// widget expands on first selection of a new item type, causing
+		// the QGraphicsView to shrink and re-map coordinates.  Screen
+		// coordinates are stable across viewport changes; scene coords
+		// are not — so use screenPos() for the threshold check.
+		const QPointF d = event->screenPos() - event->buttonDownScreenPos(Qt::LeftButton);
+		if (d.manhattanLength() < QApplication::startDragDistance())
+			return;
 		m_first_move = false;
-		return;
 	}
 
-	if((event->buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable))
-	{
+	if ((event->buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable)) {
 		QPointF pos = event->scenePos() + (m_origin_pos - event->buttonDownScenePos(Qt::LeftButton));
 		event->modifiers() == Qt::ControlModifier ? setPos(pos) : setPos(elementScene()->snapToGrid(pos));
-	}
-	else
+	} else {
 		QGraphicsObject::mouseMoveEvent(event);
+	}
 }
 
 void CustomElementGraphicPart::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)

sources/editor/graphicspart/partdynamictextfield.cpp

@@ -20,6 +20,7 @@
 #include "../../QPropertyUndoCommand/qpropertyundocommand.h"
 #include "../../qetapp.h"
 #include "../elementscene.h"
+#include <QApplication>
 
 #include <QColor>
 #include <QFont>
@@ -495,12 +496,16 @@ bool PartDynamicTextField::keepVisualRotation() const {
 	@param event
 */
 void PartDynamicTextField::mouseMoveEvent(QGraphicsSceneMouseEvent *event) {
-	if((event -> buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable)) {
-		QPointF pos = event -> scenePos() + (m_origin_pos - event -> buttonDownScenePos(Qt::LeftButton));
-		event -> modifiers() == Qt::ControlModifier ? setPos(pos) : setPos(elementScene() -> snapToGrid(pos));
-	}
-	else
+	if ((event->buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable)) {
+		// Suppress spurious moves from the properties dock resizing the viewport.
+		const QPointF d = event->screenPos() - event->buttonDownScreenPos(Qt::LeftButton);
+		if (d.manhattanLength() < QApplication::startDragDistance())
+			return;
+		QPointF pos = event->scenePos() + (m_origin_pos - event->buttonDownScenePos(Qt::LeftButton));
+		event->modifiers() == Qt::ControlModifier ? setPos(pos) : setPos(elementScene()->snapToGrid(pos));
+	} else {
 		QGraphicsObject::mouseMoveEvent(event);
+	}
 }
 
 /**

sources/editor/graphicspart/parttext.cpp

@@ -18,6 +18,7 @@
 #include "parttext.h"
 
 #include "../../QPropertyUndoCommand/qpropertyundocommand.h"
+#include <QApplication>
 #include "../../qetapp.h"
 #include "../elementprimitivedecorator.h"
 #include "../elementscene.h"
@@ -324,11 +325,14 @@ void PartText::setFont(const QFont &font) {
 }
 
 void PartText::mouseMoveEvent(QGraphicsSceneMouseEvent *event) {
-	if((event -> buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable)) {
-		QPointF pos = event -> scenePos() + (m_origin_pos - event -> buttonDownScenePos(Qt::LeftButton));
-		event -> modifiers() == Qt::ControlModifier ? setPos(pos) : setPos(elementScene() -> snapToGrid(pos));
-	}
-	else {
+	if ((event->buttons() & Qt::LeftButton) && (flags() & QGraphicsItem::ItemIsMovable)) {
+		// Suppress spurious moves from the properties dock resizing the viewport.
+		const QPointF d = event->screenPos() - event->buttonDownScreenPos(Qt::LeftButton);
+		if (d.manhattanLength() < QApplication::startDragDistance())
+			return;
+		QPointF pos = event->scenePos() + (m_origin_pos - event->buttonDownScenePos(Qt::LeftButton));
+		event->modifiers() == Qt::ControlModifier ? setPos(pos) : setPos(elementScene()->snapToGrid(pos));
+	} else {
 		QGraphicsObject::mouseMoveEvent(event);
 	}
 }