Add Widget::isDescendantOf(). Only scroll RackScrollWidget when dragging a child of its container with the left mouse button.

include/widget/Widget.hpp

@@ -54,6 +54,9 @@ struct Widget : WeakBase {
 	*/
 	virtual math::Rect getChildrenBoundingBox();
 	virtual math::Rect getVisibleChildrenBoundingBox();
+	/** Returns whether `ancestor` is a parent or distant parent of this widget.
+	*/
+	bool isDescendantOf(Widget* ancestor);
 	/**  Returns `v` (given in local coordinates) transformed into the coordinate system of `ancestor`.
 	*/
 	virtual math::Vec getRelativeOffset(math::Vec v, Widget* ancestor);

src/app/RackScrollWidget.cpp

@@ -98,7 +98,8 @@ void RackScrollWidget::step() {
 	// Scroll rack if dragging cable near the edge of the screen
 	math::Vec pos = APP->scene->mousePos;
 	math::Rect viewport = getViewport(box.zeroPos());
-	if (APP->event->getDraggedWidget()) {
+	widget::Widget* draggedWidget = APP->event->getDraggedWidget();
+	if (draggedWidget && draggedWidget->isDescendantOf(container) && APP->event->dragButton == GLFW_MOUSE_BUTTON_LEFT) {
 		float margin = 20.0;
 		float speed = 15.0;
 		if (pos.x <= viewport.pos.x + margin)

src/widget/Widget.cpp

@@ -112,6 +112,15 @@ math::Rect Widget::getVisibleChildrenBoundingBox() {
 }
 
 
+bool Widget::isDescendantOf(Widget* ancestor) {
+	if (!parent)
+		return false;
+	if (parent == ancestor)
+		return true;
+	return parent->isDescendantOf(ancestor);
+}
+
+
 math::Vec Widget::getRelativeOffset(math::Vec v, Widget* ancestor) {
 	if (this == ancestor)
 		return v;