GPU caching for better performance after many strokes

Plugins/ZShell/Internal/stroke.hpp

@@ -3,13 +3,16 @@
 #include <QColor>
 #include <QPointF>
 #include <QVector>
+#include <QCanvasPath>
 
 namespace ZShell::internal {
 
 struct Stroke {
 	QVector<QPointF> points;
+	QCanvasPath path;
 	QColor color;
 	float width;
+	int groupId = -1;
 };
 
 };

Plugins/ZShell/Internal/strokecanvasitem.cpp

@@ -1,5 +1,6 @@
 #include "strokecanvasitem.hpp"
 #include "strokecanvasrenderer.hpp"
+#include <qcanvaspainter.h>
 #include <qnamespace.h>
 
 namespace ZShell::internal {
@@ -27,6 +28,42 @@ static bool shouldAddPoint(
 	       >= minDistance * minDistance;
 }
 
+static QCanvasPath buildStrokePath(const QVector<QPointF> &points) {
+	QCanvasPath path;
+
+	if (points.size() == 1) {
+		// Single point — store as a tiny circle so the group can still be cached
+		path.circle(points[0], 0); // radius 0; actual width applied at draw time
+		return path;
+	}
+
+	auto catmullToBezier = [](
+		const QPointF &p0, const QPointF &p1,
+		const QPointF &p2, const QPointF &p3,
+		float tension,
+		QPointF &cp1, QPointF &cp2)
+			       {
+				       cp1 = p1 + (p2 - p0) * tension / 3.0f;
+				       cp2 = p2 - (p3 - p1) * tension / 3.0f;
+			       };
+
+	const float tension = 0.5f;
+	path.moveTo(points[0]);
+
+	for (int i = 0; i < points.size() - 1; ++i) {
+		const QPointF &p0 = points[qMax(i - 1, 0)];
+		const QPointF &p1 = points[i];
+		const QPointF &p2 = points[i + 1];
+		const QPointF &p3 = points[qMin(i + 2, points.size() - 1)];
+
+		QPointF cp1, cp2;
+		catmullToBezier(p0, p1, p2, p3, tension, cp1, cp2);
+		path.bezierCurveTo(cp1, cp2, p2);
+	}
+
+	return path;
+}
+
 void StrokeCanvasItem::setPenColor(const QColor &color) {
 	if (m_penColor == color)
 		return;
@@ -129,16 +166,19 @@ void StrokeCanvasItem::endStroke() {
 	if (m_currentStroke.points.isEmpty())
 		return;
 
-	m_strokes.append(m_currentStroke);
+	m_currentStroke.path = buildStrokePath(m_currentStroke.points);
+	m_currentStroke.groupId = m_nextGroupId++;
 	m_currentStroke.points.clear();
 
+	m_strokes.append(m_currentStroke);
+	m_currentStroke = {};
+
 	update();
 }
 
 void StrokeCanvasItem::clear() {
 	m_strokes.clear();
-	m_currentStroke.points.clear();
-
+	m_currentStroke = {};
 	update();
 }
 

Plugins/ZShell/Internal/strokecanvasitem.hpp

@@ -71,6 +71,7 @@ QPointF m_hoverPoint;
 QColor m_penColor = Qt::white;
 float m_penWidth = 4.f;
 
+int m_nextGroupId = 0;
 QVector<Stroke> m_strokes;
 Stroke m_currentStroke;
 };

Plugins/ZShell/Internal/strokecanvasrenderer.cpp

@@ -73,7 +73,18 @@ void StrokeCanvasRenderer::synchronizeData(QCanvasPainterItem *item) {
 	m_penColor = canvas->m_penColor;
 	m_penWidth = canvas->m_penWidth;
 
-	m_strokes = canvas->m_strokes;
+	// Only copy strokes the renderer hasn't seen yet
+	while (m_strokes.size() < canvas->m_strokes.size())
+		m_strokes.append(canvas->m_strokes[m_strokes.size()]);
+
+	// Handle clear()
+	if (canvas->m_strokes.isEmpty() && !m_strokes.isEmpty()) {
+		for (const auto &stroke : m_strokes)
+			if (stroke.groupId >= 0)
+				m_pendingGroupRemovals.append(stroke.groupId);
+		m_strokes.clear();
+	}
+
 	m_currentStroke = canvas->m_currentStroke;
 
 	m_hoverVisible = canvas->m_hoverVisible;
@@ -81,26 +92,30 @@ void StrokeCanvasRenderer::synchronizeData(QCanvasPainterItem *item) {
 }
 
 void StrokeCanvasRenderer::paint(QCanvasPainter *painter) {
+	for (int id : m_pendingGroupRemovals)
+		painter->removePathGroup(id);
+	m_pendingGroupRemovals.clear();
+
 	painter->clearRect(0, 0, width(), height());
 
-	for (const auto &stroke : m_strokes)
-		drawStroke(painter, stroke.points, stroke.color, stroke.width);
+	for (const auto &stroke : m_strokes) {
+		painter->setStrokeStyle(stroke.color);
+		painter->setFillStyle(stroke.color);
+		painter->setLineWidth(stroke.width);
+		painter->setLineCap(QCanvasPainter::LineCap::Round);
+		painter->setLineJoin(QCanvasPainter::LineJoin::Round);
 
-	drawStroke(
-		painter,
-		m_currentStroke.points,
-		m_currentStroke.color,
-		m_currentStroke.width
-		);
-
-	if (m_hoverVisible) {
-		drawDot(
-			painter,
-			m_hoverPoint,
-			m_penColor,
-			m_penWidth
-			);
+		if (stroke.path.commandsSize() == 1) {
+			painter->fill(stroke.path, stroke.groupId);
+		} else {
+			painter->stroke(stroke.path, stroke.groupId);
+		}
 	}
+
+	drawStroke(painter, m_currentStroke.points, m_currentStroke.color, m_currentStroke.width);
+
+	if (m_hoverVisible)
+		drawDot(painter, m_hoverPoint, m_penColor, m_penWidth);
 }
 
 };

Plugins/ZShell/Internal/strokecanvasrenderer.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <QCanvasPainterItemRenderer>
+#include <qcontainerfwd.h>
 #include "stroke.hpp"
 
 namespace ZShell::internal {
@@ -19,6 +20,7 @@ QPointF m_hoverPoint;
 
 QVector<Stroke> m_strokes;
 Stroke m_currentStroke;
+QVector<int> m_pendingGroupRemovals;
 
 };