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Escher is a collection of libraries for X Window System written purely in Java.

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package gnu.app.displayhack.eraser;

import gnu.x11.Window;
import gnu.app.displayhack.DisplayHack;


/**
 * Erase by sliding lines.
 *
 * Modified from slide_lines of erase.c in xscreensaver by Torbjorn
 * Andersson .
 *
 * 
Trivially added erase in y-direction support.
 */
public class SlideLines extends Eraser {
  /**
   * TODO
   * 1. accelerating slide?
   * 2. slide in any directions?
   */

  public static final int SLICE = 100;
  public static final int DELAY = 200;

  public SlideLines () { super ("slide-lines"); }


  public void erase (DisplayHack hack) {
    // no useless notify events
    hack.eraser_gc.set_graphics_exposures (false);

    if (hack.random.nextBoolean ())
      horizontal_erase (hack);
    else
      vertical_erase (hack);
    
    hack.sleep (hack.delay/2);  // before next screen
  }


  /** 
   * Erase in x-direction. Exactly the same as {@link
   * #vertical_erase(DisplayHack)} with x and y-related swapped.
   */
  public void horizontal_erase (DisplayHack hack) {
    Window window = hack.window;
    int dx = Math.max (1, window.width / DELAY * hack.eraser_delta);
    int dy = Math.max (1, window.height / SLICE * hack.eraser_delta);

    for (int x=0; x