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This is a backport of OpenJFX 8 to run on Java 7.
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/*
 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.javafx.scene.control.skin;

import javafx.beans.InvalidationListener;
import javafx.beans.Observable;
import javafx.scene.control.IndexedCell;
import javafx.scene.control.ScrollBar;

import com.sun.javafx.Utils;

/**
 * This custom ScrollBar is used to map the increment & decrement features
 * to pixel based scrolling rather than thumb/track based scrolling, if the
 * "virtual" attribute is true.
 */
public class VirtualScrollBar extends ScrollBar {
    private final VirtualFlow flow;

    private boolean virtual;
    
    private boolean adjusting;

    public VirtualScrollBar(final VirtualFlow flow) {
        this.flow = flow;
        
        super.valueProperty().addListener(new InvalidationListener() {
            @Override public void invalidated(Observable valueModel) {
                if (isVirtual()/* && oldValue != newValue*/) {
                    if (adjusting) {
                        // no-op
                    } else {
                        flow.setPosition(getValue());
                    }
                }
            }
        });
    }

    public void setVirtual(boolean virtual) {
        this.virtual = virtual;
    }

    public boolean isVirtual() {
        return this.virtual;
    }

    @Override public void decrement() {
        if (isVirtual()) {
            flow.adjustPixels(-10);
        } else {
            super.decrement();
        }
    }

    @Override public void increment() {
        if (isVirtual()) {
            flow.adjustPixels(10);
        } else {
            super.increment();
        }
    }
    
//    private double lastAdjustValue = 0.0;

    // this method is called when the user clicks in the scrollbar track, so
    // we special-case it to allow for page-up and page-down clicking to work
    // as expected.
    @Override public void adjustValue(double pos) {
        if (isVirtual()) {
//            if (pos == lastAdjustValue) {
//                return;
//            }

            adjusting = true;
            double oldValue = flow.getPosition();
            
            double newValue = ((getMax() - getMin()) * Utils.clamp(0, pos, 1))+getMin();
            if (newValue < oldValue) {
                IndexedCell cell = flow.getFirstVisibleCell();
                if (cell == null) return;
                flow.showAsLast(cell);
            } else if (newValue > oldValue) {
                IndexedCell cell = flow.getLastVisibleCell();
                if (cell == null) return;
                flow.showAsFirst(cell);
            }
//            lastAdjustValue = pos;
            
            adjusting = false;
        } else {
            super.adjustValue(pos);
        }
    }
}