preset color buttons rework + curve smoothing

Plugins/ZShell/Internal/strokecanvasitem.cpp

@@ -13,6 +13,20 @@ QCanvasPainterItemRenderer *StrokeCanvasItem::createItemRenderer() const {
 	return new StrokeCanvasRenderer;
 }
 
+static bool shouldAddPoint(
+	const QVector<QPointF> &points,
+	const QPointF &p,
+	qreal minDistance)
+{
+	if (points.isEmpty())
+		return true;
+
+	const QPointF delta = p - points.last();
+
+	return QPointF::dotProduct(delta, delta)
+	       >= minDistance * minDistance;
+}
+
 void StrokeCanvasItem::setPenColor(const QColor &color) {
 	if (m_penColor == color)
 		return;
@@ -44,7 +58,9 @@ void StrokeCanvasItem::beginStroke(qreal x, qreal y) {
 }
 
 void StrokeCanvasItem::appendPoint(qreal x, qreal y) {
-	m_currentStroke.points.append({x, y});
+	if (shouldAddPoint(m_currentStroke.points, {x, y}, 2.0))
+		m_currentStroke.points.append({x, y});
+
 	update();
 }
 

Plugins/ZShell/Internal/strokecanvasrenderer.cpp

@@ -28,8 +28,11 @@ static void drawStroke(
 	painter->beginPath();
 	painter->moveTo(points[0]);
 
-	for (qsizetype i = 1; i < points.size(); ++i)
-		painter->lineTo(points[i]);
+	for (int i = 1; i < points.size() - 1; ++i) {
+		QPointF mid = (points[i] + points [i + 1]) / 2;
+		painter->quadraticCurveTo(points[i], mid);
+	}
+	painter->lineTo(points.last());
 
 	painter->stroke();
 }