import java.awt.*; // to get Graphics object.

public class bendCanvas extends Canvas 
{
	Image offscreen;  // This is the offscreen image so we can double buffer.
	bendGraphic curve; 
	int imagewidth, imageheight;

	// The constructor makes the curve object with default values.
	// They can be resized.
	bendCanvas() 
	{
		this.setBackground(Color.white);
		Dimension d = this.getSize();
		imagewidth = d.width;
		imageheight = d.height;
		curve = new bendGraphic(650,450,0.0,0.0);
//		imagewidth = 650;
//		imageheight = 450;  
	}

	// A public function to allow people to change the torque_R
	// of the longer wavelength.  We pass this on to our curve object.
	public void setTorsion_R(double torque_R) 
	{
		curve.setTorsion_R(torque_R);
		this.drawCanvas();
	}
	
	public void setTorsion_L(double torque_L) 
	{
		curve.setTorsion_L(torque_L);
		this.drawCanvas();
	}

	// These two inform the layout what our minimum requirements are.
	// Without these, you may get a zero size object.
	public Dimension getPreferredSize() 
	{
		Dimension D = new Dimension(200,50);
		return D;
	}

	public Dimension getMinimumSize() 
	{
		Dimension D = new Dimension(150,50);
		return D;
	}

	// This method draws the background and  text at its current position.
	public void paint(Graphics g) 
	{
		//Dimension d = this.size();
		update(g);
	}


	public void update( Graphics g ) 
	{
		// If the screen is invalid, don't redraw.  Just copy from the
		// offscreen buffer.
		if (offscreen != null) 
		{
			g = this.getGraphics();
			g.drawImage(offscreen, 0, 0, this);
		} 
		else 
		{
			g.clearRect(0,0,imagewidth,imageheight);
		}
	}

	public void processMouseEvent(java.awt.event.MouseEvent e) 
	{
		if (e.getSource()==this) 
		{
			this.drawCanvas();
		}
	}


	public void drawCanvas() 
	{
		// Make sure the offscreen image is created and is the right size.
		Dimension d = this.getSize();
		if ((offscreen == null) ||
		((imagewidth != d.width) || (imageheight != d.height))) 
		{
			// if (offscreen != null) offscreen.flush();
			// Sometimes the image sizes are zero or negative before the
			// frame is drawn.
			if (d.width > 1 && d.height > 1) 
			{
				imagewidth = d.width;
				imageheight = d.height;
			}
			// Create an image from the size of this canvas using a method
			// from the component class, I think.
			offscreen = createImage(imagewidth, imageheight);
			// Make our curve agree to the size.
			curve.setSize(imagewidth,imageheight);
		}
           
		// Get the offscreen image.
		Graphics g;
		try 
		{
			g = offscreen.getGraphics();
		}
		catch (java.lang.NullPointerException e)
		{
			System.out.println("java.lang.NullPointerException: " + e);
			g = null;
		}

		// Draw into the off-screen image.
		g.clearRect(0,0,d.width,d.height);
		curve.draw(g);
		// Request that the system call paint sometime soon.
		repaint();	
		paint(g);
	}
}