ScrollbarVisibility.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.scrollable.context;

import static com.codeaffine.eclipse.swt.widget.scrollbar.FlatScrollBar.BAR_BREADTH;

import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Scrollable;

import com.codeaffine.eclipse.swt.util.Platform;
import com.codeaffine.eclipse.swt.util.Platform.PlatformType;

class ScrollbarVisibility {

  private final boolean horizontalBarVisible;
  private final boolean verticalBarVisible;

  ScrollbarVisibility( SizeComputer sizeComputer,
                       ScrollableControl<? extends Scrollable> scrollable,
                       Rectangle clientArea,
                       int itemHeight )
  {
    horizontalBarVisible =    scrollable.hasHorizontalBar()
                           && (    isWin32() && scrollable.isHorizontalBarVisible()
                                || computeHorizontalBarVisible( sizeComputer, clientArea ) );
    verticalBarVisible =    isWin32() && scrollable.isVerticalBarVisible()
                         || !isWin32() && computeVerticalBarVisible( sizeComputer, clientArea, itemHeight );
  }

  boolean isHorizontalBarVisible() {
    return horizontalBarVisible;
  }

  boolean isVerticalBarVisible() {
    return verticalBarVisible;
  }

  private static boolean isWin32() {
    return new Platform().matches( PlatformType.WIN32 );
  }

  private static boolean computeHorizontalBarVisible( SizeComputer sizeComputer, Rectangle clientArea ) {
    Point preferredSize = sizeComputer.getPreferredSize();
    return preferredSize.x > clientArea.width;
  }

  private boolean computeVerticalBarVisible( SizeComputer sizeComputer, Rectangle clientArea, int itemHeight ) {
    int preferredHeight = sizeComputer.getPreferredSize().y;
    int clientAreaHeight = clientArea.height;
    return computeVerticalBarVisible( horizontalBarVisible, preferredHeight, clientAreaHeight, itemHeight );
  }

  private static boolean computeVerticalBarVisible(
    boolean horizontalBarVisible, int preferredHeight, int visibleAreaHeight, int itemHeight )
  {
    if( !horizontalBarVisible ) {
      return computeVisibleItemsHeight( preferredHeight, itemHeight ) >= visibleAreaHeight;
    }
    return computeVisibleItemsHeight( preferredHeight, itemHeight ) + BAR_BREADTH - 1 >= visibleAreaHeight;
  }

  private static int computeVisibleItemsHeight( int preferredHeight, int itemHeight  ) {
    return ( preferredHeight / itemHeight ) * itemHeight;
  }
}