How to draw portions of circles based on percentages in Graphics2D?

Question

I am working on a circular health bar for a top-down 2d shooter and would like some opinions of the best way to do this in only graphics2D. Wondering if drawing many arcs or just using images would be best.

Answer 1

The answer depends on what you want to achieve...

This is a very basic example...

You can go backwards

Even start at a different angle.

With a little bit of work you could reduce the extended so you could have an "open" progress, for example, starting at 245 degrees with a total extent of 270 degrees if you wanted to

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Arc2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class CircleProgress {

    public static void main(String[] args) {
        new CircleProgress();
    }

    public CircleProgress() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new ProgressPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class ProgressPane extends JPanel {

        private float progress;
        private float startAt = 270;
        private float direction = -1;
        private Timer timer;

        public ProgressPane() {
            timer = new Timer(80, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    float value = getProgress();
                    if (value >= 1f) {
                        timer.stop();
                    }
                    setProgress(value += 0.01);
                }
            });
        }

        public void setProgress(float progress) {
            if (progress < 0.0) {
                progress = 0;
            } else if (progress > 1f) {
                progress = 1f;
            }
            this.progress = progress;
            repaint();
        }

        public float getProgress() {
            return progress;
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(100, 100);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            float extent = (360f * getProgress()) * direction;
            int width = getWidth();
            int height = getHeight();
            int radius = Math.min(width, height);

            int x = (width - radius) / 2;
            int y = (height - radius) / 2;

            g2d.setColor(Color.YELLOW);
            Arc2D arc = new Arc2D.Double(x, y, radius, radius, startAt, extent, Arc2D.PIE);
            g2d.fill(arc);

            g2d.dispose();
        }
    }

}