/*

File:	 ScrollableCanvas.java
Author:  zerksis d. umrigar (zdu@acm.org)
Copyright (C) 1997 Zerksis D. Umrigar
Last Update Time-stamp: "97/06/27 20:40:41 umrigar"

This code is distributed under the terms of the GNU General Public License.
See the file COPYING with this distribution, or

		http://www.fsf.org/copyleft/gpl.html

THERE IS ABSOLUTELY NO WARRANTY FOR THIS PROGRAM.

*/

package zdu.parsdemo;

import zdu.parsdemo.ScrollPanel;

import java.awt.*;


/** Implements a scrollable canvas with two scrollbars, which can be controlled
 * directly by subclasses.  
 * 
 * IMPORTANT NOTE:  When this canvas is to be added to a component, the
 * canvas should not be directly added; instead its getComponent() member
 * should be added.
 */
class ScrollableCanvas extends Canvas implements Runnable {

  /** Create a canvas with size width x height pixels.
   * @param width	width of canvas in pixels.
   * @param height	height of canvas in pixels.
   */
  ScrollableCanvas(int width, int height, String mouseHint) {
    if (getFont() == null) {
      super.setFont(new Font("Courier", 0, 12));
    }
    initSize= new Dimension(width, height);
    Dimension s= size();
    hScroll= new Scrollbar(Scrollbar.HORIZONTAL, 0, s.width, 0, s.width);
    hScroll.setLineIncrement(width/20 < 1 ? 1 : width/20); 
    hScroll.setPageIncrement(width - SLOP < 1 ? width : width - SLOP);
    vScroll= new Scrollbar(Scrollbar.VERTICAL, 0, s.height, 0, s.height);
    vScroll.setLineIncrement(height/20 < 1 ? 1 : height/20); 
    vScroll.setPageIncrement(height - SLOP < 1 ? height : height - SLOP);    
    panel= new ScrollPanel(this, hScroll, vScroll);
    hintMsg= mouseHint;
  }

  ScrollableCanvas(int width, int height) {
    this(width, height, null);
  }

  //Return creation size as minimum size if requested by packer.
  public Dimension minimumSize() {
    return initSize;
  }

  //Return creation size as preferred size  if requested by packer.
  public Dimension preferredSize() {
    return initSize;
  }

  //Provided double buffering.
  public void update(Graphics g) {
    Dimension s= size();
    if (buf == null || bufDim.width != s.width || bufDim.height != s.height) {
      bufDim= new Dimension(s.width, s.height);
      buf= createImage(bufDim.width, bufDim.height);
    }
    Graphics bg= buf.getGraphics();
    bg.clearRect(0, 0, bufDim.width, bufDim.height);
    paint(bg);
    bg.dispose();
    g.drawImage(buf, 0, 0, null);
    if (hintThread != null) {
      Image hintImage= getHintImage();
      if (hintImage != null) g.drawImage(hintImage, 0, 0, null);
    }
  }

  //IMPORTANT: This is the method which must be used if this is to be
  //added to a container; i.e., if logically, this is to be added to
  //a container, then add this.getComponent().
  public Component getComponent() {
    return panel;
  }

  //Entered via a hint thread.
  public void run() {
    try {
      Thread.sleep(HINT_DELAY);
    }
    catch (InterruptedException e) {
    }
    setHintThread(false, true);
  }


  public void reset() {
  }

  //The somewhat complex logic here ensures that only a single hintThread
  //is being used to paint the hint message and that if a old discarded
  //thread terminates after a new one was spawned, then the termination
  //of the old thread does not also terminate the newer one (until its
  //time has expired).
  private synchronized void setHintThread(boolean doCreate, 
					  boolean calledFromHintThread) {
    if (doCreate) {
      if (hintThread == null) {
	hintThread= new Thread(this);
	hintThread.start();
	repaint();
      }
    }
    else {
      if (hintThread != null) {
	if (calledFromHintThread) {
	  if (hintThread == Thread.currentThread()) {
	    hintThread= null; repaint();
	  }
	}
	else {
	  hintThread.interrupt(); hintThread= null; repaint();
	}
      }
    }
  }

  public boolean mouseEnter(Event event, int x, int y) {
    if (hintMsg != null) {
      setHintThread(true, false);
    }
    return false;    
  }

  public boolean mouseExit(Event event, int x, int y) {
    if (hintMsg != null) {
      setHintThread(false, false);
    }
    return false;    
  }

  Image getHintImage() {
    FontMetrics m= getFontMetrics(getFont());
    Dimension s= size();
    if (hintMsg != null && hintMsg.length() > 0 &&  
	(hintBuf == null || hintBufDim.width != s.width || 
	 hintBufDim.height != m.getHeight())) {
      hintBufDim= new Dimension(s.width, m.getHeight());
      hintBuf= createImage(hintBufDim.width, hintBufDim.height);
      Graphics g= hintBuf.getGraphics();
      g.setColor(HINT_BG_COLOR);
      g.fillRect(0, 0, s.width, m.getHeight());
      g.setColor(HINT_FG_COLOR);
      int x= (s.width - m.stringWidth(hintMsg))/2;
      g.drawString(hintMsg, x, m.getAscent());
    }
    return hintBuf;
  }

  protected Scrollbar hScroll, vScroll;	//the raison d'etre for this.
  protected static final int SLOP= 10;	//# of extra scroll pixels.
  private Image buf;			//for double buffering.
  private Dimension bufDim;		//dimensions of allocated buf.
  private Image hintBuf;		//buffer for hint message.
  private Dimension hintBufDim;		//dimensions of allocated hint buf.
  private Dimension initSize;		//size requested at creation.
  private ScrollPanel panel;		//contains scrollbars + this.
  private Thread hintThread;	        //non-null if hint being displayed.
  private String hintMsg;		//hint msg. to output on top of canvas.
  private static final Color HINT_BG_COLOR= Color.yellow;
  private static final Color HINT_FG_COLOR= Color.black;
  private static final int HINT_DELAY= 10000;

  //Trivial test program.  Can't get it to do anything particularly
  //interesting unless I subclass this.
  static public void main(String args[]) {
    Frame f= new Frame("ScrollableCanvas Test");
    ScrollableCanvas c= new ScrollableCanvas(200, 200, "mouse hint");
    f.add("Center", c.getComponent());
    f.resize(400, 400);
    f.show();
  }
}