Drawing smoothed shapes and rotating them in Java

Question

Background

Im Total Java newbie, today I started learning it (from thenewboston.org ). I already know how to create simple windows / forms / gui, draw lines, etc.

My goal is to create in Java gauge as follows:

This is a metric that I created in .NET C # WPF, and now I want to rewrite it in Java.

The main question :

How to create a triangle or other shape with some transparency and rotate it?

I tried to draw something using a Graphics object as follows:

public void paint(Graphics g){ g.drawLine(0, 0, 100, 100); } 

But I think that this is the wrong direction, because when I impose something on the schedule, it just stays there, I can’t move or rotate it.

Do I need to clear all the graphics and draw it again to make an “animation”, or is there an easier way?

---

Edit: I already know how to smooth ( Hovercraft Full Eels already helped me with this - thanks).

---

Edit2:

My code looks something like this:

 import java.awt.BasicStroke; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Point; import java.awt.RenderingHints; import javax.swing.JFrame; import javax.swing.JPanel; public class MainWindow extends JPanel { private Point p1 = new Point(100, 100); private Point p2 = new Point(740, 450); public MainWindow() { this.setPreferredSize(new Dimension(800, 600)); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); drawLines(g); } private void drawLines(Graphics g) { Graphics2D g2d = (Graphics2D) g; g2d.setColor(Color.DARK_GRAY); g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2d.setStroke(new BasicStroke(4, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND)); g.drawLine(p1.x, p1.y, p2.x, p2.y); } private void display() { JFrame f = new JFrame("Main Window"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.add(this); f.pack(); f.setLocationRelativeTo(null); f.setVisible(true); } public static void main(String[] args) { new MainWindow().display(); } } 

Answer 1

You declare:

I tried to draw something using a Graphics object as follows:

 public void paint(Graphics g){ g.drawLine(0, 0, 100, 100); } 

But I think that this is the wrong direction, because when I put something on the schedule, it just stays there, I can’t move or rotate it.

Do I need to clear all the graphics and draw it again to make an “animation”, or is there an easier way?

Suggestions:

• Do not hard code your numbers. Instead, use class fields (variables) so that your program can easily change the position of elements that were easily drawn.
• Do not override the paint(...) component paint(...) . Instead, override the object's paintComponent(Graphics g) method, which comes from a JComponent or one of its children, such as JPanel. This will give you the benefit of automatic double buffering for smoother animations, and also reduce the chance of mistakenly drawing children or borders.
• Pass your Graphics object to a Graphics2D object so you can make a more advanced drawing using classes that implement the Shape interface, including Rectangle2D, Ellipse2D, Line2D, Path2D, and many others.
• Draw the background image as a BufferedImage using the Graphics#drawImage(...) method, and then draw moving images on top of it, again using the Graphics2D object and again changing the images created based on the state of the object (values ​​held by its fields).
• Be careful when performing animations that obey the Swing rules for streaming, that you do not have any animation or game loops that link the Swing stream. The Swing timer allows you to create a quick and simple (albeit somewhat primitive) game loop.

For instance:

 import java.awt.BasicStroke; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.RenderingHints; import java.awt.Stroke; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.geom.Point2D; import java.awt.image.BufferedImage; import javax.swing.*; public class DailAnimation extends JPanel { private static final int PREF_W = 400; private static final int PREF_H = 350; private static final Point2D CENTER = new Point2D.Double(PREF_W / 2.0, PREF_W / 2.0); private static final double RADIUS = PREF_W / 2.0; private static final Color LARGE_TICK_COLOR = Color.green; private static final Color CENTER_HUB_COLOR = Color.LIGHT_GRAY; private static final Stroke LARGE_TICK_STROKE = new BasicStroke(3f); private static final int LRG_TICK_COUNT = 9; private static final double TOTAL_LRG_TICKS = 12; private static final double LRG_TICK_OUTER_RAD = 0.9; private static final double LRG_TICK_INNER_RAD = 0.8; private static final int START_TICK = 10; private static final double CENTER_HUB_RADIUS = 10; public static final int MAX_SPEED = 100; private static final double INIT_SPEED = 0; private static final double DIAL_INNER_RAD = 0.02; private static final double DIAL_OUTER_RAD = 0.75; private static final Color DIAL_COLOR = Color.DARK_GRAY; private BufferedImage backgroundImg; private double speed; private double theta; private double cosTheta; private double sinTheta; public DailAnimation() { setBackground(Color.white); backgroundImg = createBackgroundImg(); setSpeed(INIT_SPEED); } public void setSpeed(double speed) { if (speed < 0) { speed = 0; } else if (speed > MAX_SPEED) { speed = MAX_SPEED; } this.speed = speed; this.theta = ((speed / MAX_SPEED) * LRG_TICK_COUNT * 2.0 + START_TICK) * Math.PI / TOTAL_LRG_TICKS; cosTheta = Math.cos(theta); sinTheta = Math.sin(theta); repaint(); } private BufferedImage createBackgroundImg() { BufferedImage img = new BufferedImage(PREF_W, PREF_H, BufferedImage.TYPE_INT_ARGB); Graphics2D g2 = img.createGraphics(); g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2.setColor(LARGE_TICK_COLOR); g2.setStroke(LARGE_TICK_STROKE); for (int i = 0; i < LRG_TICK_COUNT; i++) { double theta = (i * 2.0 + START_TICK) * Math.PI / TOTAL_LRG_TICKS; double cosTheta = Math.cos(theta); double sinTheta = Math.sin(theta); int x1 = (int) (LRG_TICK_INNER_RAD * RADIUS * cosTheta + CENTER.getX()); int y1 = (int) (LRG_TICK_INNER_RAD * RADIUS * sinTheta + CENTER.getY()); int x2 = (int) (LRG_TICK_OUTER_RAD * RADIUS * cosTheta + CENTER.getX()); int y2 = (int) (LRG_TICK_OUTER_RAD * RADIUS * sinTheta + CENTER.getY()); g2.drawLine(x1, y1, x2, y2); } g2.setColor(CENTER_HUB_COLOR); int x = (int) (CENTER.getX() - CENTER_HUB_RADIUS); int y = (int) (CENTER.getY() - CENTER_HUB_RADIUS); int width = (int) (2 * CENTER_HUB_RADIUS); int height = width; g2.fillOval(x, y, width, height); // g2.draw(ellipse); g2.dispose(); return img; } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); if (backgroundImg != null) { g.drawImage(backgroundImg, 0, 0, this); } Graphics2D g2 = (Graphics2D) g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setColor(DIAL_COLOR); int x1 = (int) (DIAL_INNER_RAD * RADIUS * cosTheta + CENTER.getX()); int y1 = (int) (DIAL_INNER_RAD * RADIUS * sinTheta + CENTER.getY()); int x2 = (int) (DIAL_OUTER_RAD * RADIUS * cosTheta + CENTER.getX()); int y2 = (int) (DIAL_OUTER_RAD * RADIUS * sinTheta + CENTER.getY()); g.drawLine(x1, y1, x2, y2); } @Override public Dimension getPreferredSize() { return new Dimension(PREF_W, PREF_H); } private static void createAndShowGui() { final DailAnimation mainPanel = new DailAnimation(); JFrame frame = new JFrame("DailAnimation"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(mainPanel); frame.pack(); frame.setLocationByPlatform(true); frame.setVisible(true); int delay = 100; new Timer(delay, new ActionListener() { int speed = 0; @Override public void actionPerformed(ActionEvent evt) { speed ++; if (speed > DailAnimation.MAX_SPEED) { ((Timer)evt.getSource()).stop(); } mainPanel.setSpeed(speed); } }).start(); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGui(); } }); } } 

Answer 2

Drawing a line using Graphics.drawLine() writes pixels directly to everything that supports the Graphics instance. If you want to rotate a line, you must calculate what its coordinates should be when turning. This is the only way to draw things in AWT and Swing.

You can write a needle class that has retained its angle, and then process its rendering in each frame.