ShiftData.java

/**
 * Copyright (c) 2014 - 2017 Frank Appel
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Frank Appel - initial API and implementation
 */
package com.codeaffine.eclipse.swt.widget.scrollbar;

import static com.codeaffine.eclipse.swt.widget.scrollbar.ComponentDistribution.divide;

class ShiftData {

  private final int slidePixels;
  private final int movedPixels;
  private final int buttonLength;

  ShiftData( int buttonLength, int scrollBarPixels, int dragPixels, int movedPixels ) {
    this.buttonLength = buttonLength;
    this.slidePixels = calculateSlidePixels( scrollBarPixels, dragPixels );
    this.movedPixels = movedPixels;
  }

  boolean canShift( ) {
    return slidePixels > 0;
  }

  int calculateSelectionDelta( int selectionRange ) {
    return divide( movedPixels * selectionRange, slidePixels );
  }

  static int calculateSelectionRange( FlatScrollBar scrollBar ) {
    return scrollBar.getMaximum() - scrollBar.getMinimum() - scrollBar.getThumb();
  }

  private int calculateSlidePixels( int scrollBarPixels, int dragPixels ) {
    return scrollBarPixels - 2 * buttonLength - dragPixels;
  }
}