ADDITIONAL SYSTEM INFORMATION :
Java 11: 
openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)

Java 8:
openjdk version "1.8.0-adoptopenjdk"
OpenJDK Runtime Environment (build 1.8.0-adoptopenjdk-_2018_05_19_00_59-b00)
OpenJDK 64-Bit Server VM (build 25.71-b00, mixed mode)

System:
Windows 10 64-bit Pro 1803, build 17134.320, Intel core i7
Intel graphics, display scaling 125% (default)


A DESCRIPTION OF THE PROBLEM :
drawPolyline seems to be a lot slower on Java 11, compared to Java 8, running exactly the same JAR. I saw this on a graphing application with very detailed graphs. I have also reproduced this with test code. On the test code, the paint routine executes in < 100ms on Java 8 but takes over 20 seconds on Java 11.

REGRESSION : Last worked in version 8u181

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a Java program with a JFrame containing a custom subclass of JComponent
2. Implement the component's paintComponent method to include 
        graphics.drawPolyline(xs, ys, xs.length);
where xs and ys are two pre-initialised, large int[] arrays
3. Build and run using JDK8 and JDK11
4. Resize the frame to force a repaint
(I have a complete Netbeans project to attach)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Both should work about the same (JDK11 window is bigger because of HiDPI scaling)
ACTUAL -
JDK11 is much slower, many seconds elapse between resizing the window and the display refreshing

---------- BEGIN SOURCE ----------
=== canvas.java ===
package polylinetest;

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.util.Random;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JComponent;

public class Canvas extends JComponent {

    public static int SIZEGRADE = 16;

    public Canvas() {
        Random rnd = new Random();
        int len = 1 << SIZEGRADE;
        xs = new int[len];
        ys = new int[len];
        for (int i = 0; i < len; ++i) {
            xs[i] = rnd.nextInt(640);
            ys[i] = rnd.nextInt(480);
        }
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D graphics = (Graphics2D) g;
        long starttime = System.nanoTime();
        graphics.drawPolyline(xs, ys, xs.length);
        long endtime = System.nanoTime();
        Logger.getLogger(this.getClass().getName()).log(Level.INFO, "Paint Time: {0}s", (double) (endtime - starttime) / 1.0e9);
    }
    private final int[] xs;
    private final int[] ys;
}
======

=== PolylineTest.java ===
package polylinetest;

import javax.swing.JFrame;

public class PolylineTest {
    public static void main(String[] args) {
        JFrame frame = new JFrame("polyline test");
        frame.setSize(640, 480);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new Canvas());
        javax.swing.SwingUtilities.invokeLater(() -> frame.setVisible(true));
    }
    
}
======
---------- END SOURCE ----------

FREQUENCY : always