Why my arc is jumping

Change the m_angle increment to 1 and increase the sleep delay to 200ms to see what happens

to the arc with each successive rendering.

I tried two things to smooth out the animation:

1 — create an arc and animate it with AffineTransform

2 — create an image of the arc and rotate it with AffineTransform.

import java.awt.BasicStroke;

import java.awt.Color;

import java.awt.GradientPaint;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.GraphicsConfiguration;

import java.awt.GraphicsEnvironment;

import java.awt.GraphicsDevice;

import java.awt.Rectangle;

import java.awt.RenderingHints;

import java.awt.Transparency;

import java.awt.geom.AffineTransform;

import java.awt.geom.Arc2D;

import java.awt.geom.Rectangle2D;

import java.awt.image.BufferedImage;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.WindowConstants;

public class ArcTestRx extends JPanel{

Arc2D arc;

GradientPaint gp;

BufferedImage image;

private int m_angle = 0;

public ArcTestRx(){

arc = new Arc2D.Double(0, 0, 30, 30, 0, 280, Arc2D.OPEN);

Color start = Color.GRAY;

Color end= Color.WHITE;

gp = new GradientPaint(30, 30, start, 60, 60, end);

createImage();

Animate anim = new Animate();

anim.start();

}

public void paintComponent(Graphics g){

super.paintComponent(g);

Graphics2D g2d = (Graphics2D)g;

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION,

RenderingHints.VALUE_INTERPOLATION_BICUBIC);

g2d.setStroke(new BasicStroke(5f));

//g2d.setPaint(gp);

g2d.drawArc(30, 30, 30, 30, m_angle, 280);

//arc.setArc(30, 30, 30, 30, m_angle, 280, Arc2D.OPEN);

//g2d.draw(arc);

double radians = Math.toRadians(m_angle);

Rectangle2D r = arc.getBounds2D();

// arc angles are measured positive anti-clockwise

// the rest of java measures angles positive clockwise

// can we draw a smoother animation using AffineTransform

// to rotate an Arc2D?

AffineTransform at = AffineTransform.getTranslateInstance(300, 30);

at.rotate(-radians, r.getCenterX(), r.getCenterY());

g2d.draw(at.createTransformedShape(arc));

// how about rotating an image of the Arc2D with AffineTransform?

at.setToTranslation(200, 200);

at.rotate(-radians, image.getWidth()/2, image.getHeight()/2);

g2d.drawRenderedImage(image, at);

}

private void createImage(){

BasicStroke stroke = new BasicStroke(5f);

float lineWidth = stroke.getLineWidth();

Rectangle r = arc.getBounds();

int w = (int)(r.width + lineWidth);

int h = (int)(r.height + lineWidth);

image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);

Graphics2D g2 = image.createGraphics();

g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,

RenderingHints.VALUE_INTERPOLATION_BICUBIC);

g2.setPaint(Color.black);

g2.setStroke(new BasicStroke(5f));

g2.translate(lineWidth/2.0, lineWidth/2.0);

g2.draw(arc);

g2.dispose();

}

public static void main(String[] args) {

JFrame f = new JFrame();

ArcTestRx t = new ArcTestRx();

f.add(t);

f.setSize(400, 400);

f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

f.setVisible(true);

}

class Animate extends Thread{

public void run(){

while(true){

ArcTestRx.this.repaint();

m_angle += 10;

if(m_angle > 360){

m_angle = 0;

}

try {

Thread.sleep(20);

} catch (InterruptedException e) {}

}

}

}

}

74philipa at 2007-7-14 20:45:27 >

import java.awt.BasicStroke;

import java.awt.BorderLayout;

import java.awt.Color;

import java.awt.GradientPaint;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.RenderingHints;

import javax.swing.ImageIcon;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JPanel;

import javax.swing.UIManager;

import javax.swing.WindowConstants;

public class ArcTestRx extends JPanel{

Color start, end;

private int m_angle = 0;

public ArcTestRx(){

start = Color.GRAY;

end= UIManager.getColor("Panel.background");

setLayout(new BorderLayout());

add(new JLabel(new ImageIcon("loading.gif")), "First");

Animate anim = new Animate();

anim.start();

}

public void paintComponent(Graphics g){

super.paintComponent(g);

Graphics2D g2d = (Graphics2D)g;

g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

RenderingHints.VALUE_ANTIALIAS_ON);

g2d.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,

RenderingHints.VALUE_STROKE_PURE);

g2d.setStroke(new BasicStroke(5f));

GradientPaint gp = getGradient();

g2d.setPaint(gp);

g2d.drawArc(30, 30, 30, 30, m_angle, 180);

}

private GradientPaint getGradient() {

int cx = 45;

int cy = 45;

double radius = (30 + 1)/2.0;

double theta = -Math.toRadians(m_angle);

float x2 = (float)(cx + radius*Math.cos(theta));

float y2 = (float)(cy + radius*Math.sin(theta));

float x1 = (float)(cx + radius*Math.cos(theta+Math.PI));

float y1 = (float)(cy + radius*Math.sin(theta+Math.PI));

return new GradientPaint(x1, y1, start, x2, y2, end);

}

public static void main(String[] args) {

JFrame f = new JFrame();

ArcTestRx t = new ArcTestRx();

f.add(t);

f.setSize(240, 120);

f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

f.setVisible(true);

}

class Animate extends Thread{

public void run(){

while(true){

ArcTestRx.this.repaint();

m_angle += 10;

if(m_angle > 360){

m_angle = 0;

}

try {

Thread.sleep(20);

} catch (InterruptedException e) {}

}

}

}

}

74philipa at 2007-7-14 20:45:27 >