perf: optimize plotting pipeline and reduce allocations

- Reused Point2D.Double instances in Plotter to avoid per-row allocations
  → replaces new Point2D.Double() calls with setLocation() in hot loops
- Hoisted plot type lookup out of the inner loop to reduce repeated branching
- Cached FG colors locally and avoided redundant get/set calls during plotting
- Avoided repeated setStroke() calls by tracking stroke width in Canvas
- Avoided redundant setColor() calls by caching current FG color in Canvas
- Removed unused Canvas.getGraphics() accessor and simplified image lifecycle
- Switched PlotData nodes storage from Vector to ArrayList to remove synchronization overhead
- Minor cleanup in line drawing path (removed redundant operations)

Result: significantly reduced per-frame overhead, fewer allocations, and faster plotting,
especially for large datasets and during interactive redraws.

Profiled using VisualVM

Author: babaissarkar

src/main/java/com/babai/ssplot/math/plot/Canvas.java

@@ -39,6 +39,7 @@ public class Canvas {
 	private boolean axesVisible = true;
 	private boolean axes3d = false;
 	private int curNoTics = 10;
+	private int strokeWidth = 1;
 	private BufferedImage img; /* The image */
 	private Graphics2D g;
 	private Color fgColor, bgColor, axesColor, ticColor, titleColor;
@@ -110,16 +111,9 @@ private Graphics2D initImage(int W, int H) {
 		return g2;
 	}
 
-	public Graphics2D getGraphics() {
-		return g;
-	}
-
 	public BufferedImage getImage() {
-		return img;
-	}
-
-	public void dispose() {
 		g.dispose();
+		return img;
 	}
 
 
@@ -138,7 +132,6 @@ public void drawPoint(Point2D.Double p, PlotData.PointType ptype, double sizeX,
 	/** Draws a line from point q1 to point q2 */
 	public void drawLine(Point2D.Double q10, Point2D.Double q20) {
 		g.draw(new Line2D.Double(q10, q20));
-
 	}
 
 	/** Draws an vector, by drawing a line with a marker.*/
@@ -345,12 +338,17 @@ public void drawTitle(String title) {
 	/*********************************** Property Getters/Setters ************************************************/
 
 	public void setStroke(int width) {
-		g.setStroke(new BasicStroke(width));
+		if (strokeWidth != width) {
+			strokeWidth = width;
+			g.setStroke(new BasicStroke(width));
+		}
 	}
 
 	public void setFGColor(Color c) {
-		fgColor = c;
-		g.setColor(c);
+		if (!fgColor.equals(c)) {
+			fgColor = c;
+			g.setColor(c);
+		}
 	}
 
 	public Color getFGColor() {

src/main/java/com/babai/ssplot/math/plot/PlotData.java

@@ -66,7 +66,7 @@ public String toString() {
 	public enum PointType { SQUARE, CIRCLE };
 
 	private double[][] data;
-	private Vector<Node> nodes;
+	private List<Node> nodes;
 	private EquationSystem system;
 	private Axis[] axes = Axis.Cartesian.values();
 
@@ -92,7 +92,7 @@ public enum PointType { SQUARE, CIRCLE };
 
 	public PlotData(double[][] extData) {
 		data = extData;
-		nodes = new Vector<Node>();
+		nodes = new ArrayList<Node>();
 
 		// Cosmetic point properties
 		pointType = PointType.SQUARE;
@@ -238,8 +238,8 @@ public double getMin(int dataCol) {
 
 	// ------------------ NODE METHODS -------------------
 	public void addNode(Point2D.Double p, String str, Color c) { nodes.add(new Node(p, str, c)); }
-	public Vector<Node> getNodes() { return nodes; }
-	public void setNodes(Vector<Node> nodes) { this.nodes = nodes; }
+	public List<Node> getNodes() { return nodes; }
+	public void setNodes(List<Node> nodes) { this.nodes = nodes; }
 
 
 	// ------------------- STRING REPRESENTATION --------------

src/main/java/com/babai/ssplot/math/plot/Plotter.java

@@ -71,19 +71,22 @@ private void plotData(PlotData pdata, int lastIndex) {
 			dataCols[i] = pdata.getDataCol(i);
 		}
 
-		Point2D.Double p1 = null, p2 = null;
+		Point2D.Double p1 = new Point2D.Double(), p2 = new Point2D.Double(), pback = new Point2D.Double();
 
 		var dataset = pdata.getData();
 		if (lastIndex > dataset.length) {
 			lastIndex = dataset.length;
 		}
 
-		canv.setFGColor(pdata.getFgColor());
-		canv.setAxes3d(pdata.getColumnCount() == 3);
-		canv.setProjection(p);
-		canv.setStroke(pdata.ptX);
-		Color fgColor = canv.getFGColor();
+		Color fgColor = pdata.getFgColor();
 		Color fgColor2 = pdata.getFgColor2();
+		canv.setFGColor(fgColor);
+		if (pdata.getColumnCount() == 3) {
+			canv.setAxes3d(true);
+			canv.setProjection(p);
+		}
+		canv.setStroke(pdata.ptX);
+		var ptype = pdata.getPlotType();
 
 		double[] row;
 
@@ -92,13 +95,15 @@ private void plotData(PlotData pdata, int lastIndex) {
 		for (int i = 0; i < lastIndex; i++) {
 			row = dataset[i];
 
-			switch(pdata.getPlotType()) {
+			switch(ptype) {
 				case VFIELD -> {
 					// For now, it works for vector data in first four columns only
 					// TODO custom column mapping
 					if (row.length >= 4) {
-						p1 = canv.cartesianToJava(new Point2D.Double(row[0], row[1]));
-						p2 = canv.cartesianToJava(new Point2D.Double(row[2], row[3]));
+						p1.setLocation(row[0], row[1]);
+						p1 = canv.cartesianToJava(p1);
+						p2.setLocation(row[2], row[3]);
+						p2 = canv.cartesianToJava(p2);
 						canv.drawVector(p1, p2, fgColor2);
 					} else {
 						System.err.println("Bad vector field data!");
@@ -127,26 +132,23 @@ private void plotData(PlotData pdata, int lastIndex) {
 				}
 
 				case POINTS, LINES, LINES_POINTS -> {
-					p2 = canv.cartesianToJava(new Point2D.Double(row[dataCols[0]], row[dataCols[1]]));
+					p2.setLocation(row[dataCols[0]], row[dataCols[1]]);
+					p2 = canv.cartesianToJava(p2);
 
 					if (p1 != null) {
-						switch(pdata.getPlotType()) {
+						switch(ptype) {
 							case LINES -> canv.drawLine(p1, p2);
 
 							case POINTS -> canv.drawPoint(p1, PlotData.PointType.SQUARE, pdata.ptX, pdata.ptY);
 
+							// The line is drawn with plot FGcolor 1
+							// the points on the top is drawn with plot FGcolor 2
+							// FIXME generalization needed
 							case LINES_POINTS -> {
-								Point2D.Double pback = new Point2D.Double(
-									p1.getX() - (pdata.ptX+4)/2,
-									p1.getY() - (pdata.ptY+4)/2);
-								// The line is drawn with plot FGcolor 1
-								// the points on the top is drawn with plot FGcolor 2
-								// FIXME generalization needed
+								pback.setLocation(p1.x - (pdata.ptX+4)/2, p1.y - (pdata.ptY+4)/2);
 								canv.drawLine(p1, p2);
-								
 								canv.setFGColor(fgColor2);
 								canv.drawPoint(pback, PlotData.PointType.CIRCLE, pdata.ptX+4, pdata.ptY+4);
-								canv.setFGColor(fgColor);
 							}
 
 							default -> {}
@@ -157,8 +159,6 @@ private void plotData(PlotData pdata, int lastIndex) {
 				}
 			}
 		}
-		
-		canv.setStroke(1);
 	}
 
 	private void plotOthers(PlotData pdata) {