Language Java Nosugar Graphics Common Threadedcanvas.java

//	ThreadedCanvas class
//	part of the set of documents known as Java no sugar.
//	Copyright (c) 1996 Sunil Gupta, sunil@magnetic.demon.co.uk
//	placed into the public domain by the author
//
import java.awt.*;
public abstract class ThreadedCanvas extends Canvas implements Runnable
{
	//###################################################################
	// instance variables
	//###################################################################
	Thread painter = null;
	Rectangle rect;
	Image mem_image;
	boolean clear_it = true;
		
	//###################################################################
	// things that must be implemented by subclass
	//###################################################################
	public abstract Dimension minimumSize();
	public abstract void onRun(Graphics g);
	public abstract void onLoop( Graphics g);
	
	//###################################################################
	public Dimension preferredSize()
	{
		return minimumSize();
	}
	
	//****************************************************************
	public void set_clear_flag( boolean flag)
	{
		clear_it = flag;
	}
	
	//****************************************************************
	public void reshape(int x, int y, int w, int h)
	{
		super.reshape(x,y,w,h);
		set_mem_image(w,h);
	}
	//*******************************************************************
	public void addNotify()
	{
		super.addNotify();
		set_mem_image(minimumSize().width, minimumSize().height);
	}
	
	//*******************************************************************
	void set_mem_image( int w, int h)
	{
		//---------------------------------------------------------------
		rect = new Rectangle(0,0,w, h);
		mem_image = createImage(w, h);
		clearCanvas();
	}
	
	//*******************************************************************
	public Graphics getGraphics()
	{
		if (mem_image != null)
			return mem_image.getGraphics();
		else
			return null;
	}
	
	//*******************************************************************
	public void paint(Graphics g)
	{
		g.drawImage(mem_image, 0, 0, this);
	}
	//*******************************************************************
	public void update(Graphics g)
	{
		paint(g);
	}
	
	//*******************************************************************
	public void clearCanvas()
	{
		Graphics g = getGraphics();
		
		g.setColor(getBackground());
		g.fillRect(0,0,rect.width, rect.height);
		g.setColor(Color.black);
		g.drawRect(0,0, rect.width-1, rect.height-1);
	}
	
	//###################################################################
	// THREADS 
	//###################################################################
	public void start()
	{
		if (painter == null)
			painter = new Thread(this);
	
		if ( ! painter.isAlive() )
			painter.start();
	}
	
	//****************************************************************
	public void stop()
	{
		if (painter != null)
		{
			painter.stop();
			painter = null;
		}
	}
	
	//****************************************************************
	public void run()
	{
		Graphics mem_g,screen_g;
		// ******************clear the drawing surface*****************
		mem_g = getGraphics();
		screen_g = super.getGraphics();
		onRun(mem_g);
				
		// ******************draw the selected shape*************************
		while (true)
		{
			if (clear_it)
			{
				clearCanvas();
			}
				
			onLoop(mem_g);
			
			//repaint();
			paint(screen_g);
					
			//------------now let other things happen---------------
			Thread.yield();
		}
	}
	
}

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