A ScrollPane that centers on a particular actor.

PickScrollPane.java

package com.badlogic.gdx.tests.examples;

import com.badlogic.gdx.math.MathUtils;
import com.badlogic.gdx.scenes.scene2d.Actor;
import com.badlogic.gdx.scenes.scene2d.ui.ScrollPane;
import com.badlogic.gdx.scenes.scene2d.ui.Skin;
import com.badlogic.gdx.scenes.scene2d.ui.Table;
import com.badlogic.gdx.utils.Array;

public class PickScrollPane extends ScrollPane {

	private float pickAmountX;
	private float pickDifferenceX = -1;

	private boolean wasPanDragFling = false;

	private float scrollToPickedSpeed = 2500;

	public void setScrollToPickedSpeed (float scrollToPickedSpeed) {
		this.scrollToPickedSpeed = scrollToPickedSpeed;
	}

	public PickScrollPane (Actor widget) {
		super(widget);
		setFlingTime(0.0f);
	}

	public PickScrollPane (Actor widget, Skin skin) {
		super(widget, skin);
		setFlingTime(0.0f);
	}

	public PickScrollPane (Actor widget, Skin skin, String styleName) {
		super(widget, skin, styleName);
		setFlingTime(0.0f);
	}

	public PickScrollPane (Actor widget, ScrollPaneStyle style) {
		super(widget, style);
		setFlingTime(0.0f);
	}

	@Override
	public void act (float delta) {
		super.act(delta);
		if (wasPanDragFling && !isPanning() && !isDragging() && !isFlinging()) {
			wasPanDragFling = false;
			scrollToPicked();
		} else {
			if (isPanning() || isDragging() || isFlinging()) {
				wasPanDragFling = true;
			}
		}
		if (pickDifferenceX != -1) {
			float diff = scrollToPickedSpeed * delta;
			float amountX = getScrollX();

			if (pickDifferenceX > 0) {
				amountX += diff;
				setScrollX(amountX);
				pickDifferenceX -= diff;
				if (pickDifferenceX < 0 || amountX >= pickAmountX) {
					pickDifferenceX = -1;
					setScrollX(pickAmountX);
				}
			} else if (pickDifferenceX < 0) {
				amountX -= diff;
				setScrollX(amountX);
				pickDifferenceX += diff;
				if (pickDifferenceX > 0 || amountX <= pickAmountX) {
					pickDifferenceX = -1;
					setScrollX(pickAmountX);
				}
			}
		}

	}

	private void scrollToPicked () {
		final float width = getWidth();
		final float scrollX = getScrollX();
		final float maxX = getMaxX();
		
		Actor widget = getWidget();
		if (widget instanceof Table) {
			Table table = (Table)widget;
			if (scrollX >= maxX || scrollX <= 0) {
				return;
			}
			if (widget instanceof Table) {
				Table myTable = (Table)widget;
				Array<Actor> tableActors = myTable.getChildren();
				float pickedX = 0;
				float pickedWidth = 0;
				if (tableActors.size > 0) {
					for (Actor a : tableActors) {
						pickedX = a.getX();
						pickedWidth = a.getWidth();
						if (scrollX < (pickedX + pickedWidth * 0.5)) {
							break;
						}
					}
					pickDifferenceX = pickedX - scrollX - (width - pickedWidth) / 2;
					if (pickDifferenceX == 0) {
						pickDifferenceX = -1;
					}
					pickAmountX = MathUtils.clamp(pickedX - (width - pickedWidth) / 2, 0, maxX);					
				}
			}
		}
	}
}

PickScrollPaneTest.java

/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx.tests.examples;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.scenes.scene2d.Actor;
import com.badlogic.gdx.scenes.scene2d.InputEvent;
import com.badlogic.gdx.scenes.scene2d.InputListener;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Label;
import com.badlogic.gdx.scenes.scene2d.ui.ScrollPane;
import com.badlogic.gdx.scenes.scene2d.ui.Skin;
import com.badlogic.gdx.scenes.scene2d.ui.Slider;
import com.badlogic.gdx.scenes.scene2d.ui.Table;
import com.badlogic.gdx.scenes.scene2d.ui.TextButton;
import com.badlogic.gdx.scenes.scene2d.ui.TextButton.TextButtonStyle;
import com.badlogic.gdx.scenes.scene2d.utils.Align;
import com.badlogic.gdx.scenes.scene2d.utils.ChangeListener;
import com.badlogic.gdx.scenes.scene2d.utils.ClickListener;
import com.badlogic.gdx.tests.utils.GdxTest;
import com.esotericsoftware.tablelayout.Value;

public class PickScrollPaneTest extends GdxTest {
	private Stage stage;
	private Table container;

	public void create () {
		stage = new Stage(0, 0, false);
		Skin skin = new Skin(Gdx.files.internal("data/uiskin.json"));
		Gdx.input.setInputProcessor(stage);

		container = new Table();
		stage.addActor(container);
		container.setFillParent(true);

		Table table = new Table();
		table.defaults().space(100);
		Table levels1 = new Table().pad(50);
		Table levels2 = new Table().pad(50);
		Table levels3 = new Table().pad(50);
		Table levels4 = new Table().pad(50);
		
		table.debug();
		levels1.debug();
		levels2.debug();
		levels3.debug();
		levels4.debug();
		
		int c = 1;
		
		for (int y = 0; y < 3; y++) {
			levels1.row();
			for (int x = 0; x < 4; x++) {
				TextButton label = new TextButton(Integer.toString(c), skin);
				label.setName("Level" + Integer.toString(c));
				label.addListener(levelClickListener);				
				levels1.add(label).expand().fill();
				c++;
			}
		}

		for (int y = 0; y < 3; y++) {
			levels2.row();
			for (int x = 0; x < 4; x++) {
				TextButton label = new TextButton(Integer.toString(c), skin);
				label.setName("Level" + Integer.toString(c));
				label.addListener(levelClickListener);	
				levels2.add(label).expand().fill();
				c++;
			}
		}
		
		for (int y = 0; y < 3; y++) {
			levels3.row();
			for (int x = 0; x < 4; x++) {
				TextButton label = new TextButton(Integer.toString(c), skin);
				label.setName("Level" + Integer.toString(c));
				label.addListener(levelClickListener);	
				levels3.add(label).expand().fill();
				c++;
			}
		}
		
		for (int y = 0; y < 3; y++) {
			levels4.row();
			for (int x = 0; x < 4; x++) {
				TextButton label = new TextButton(Integer.toString(c), skin);
				label.setName("Level" + Integer.toString(c));
				label.addListener(levelClickListener);	
				levels4.add(label).expand().fill();
				c++;
			}
		}
		table.add(levels1).width(Gdx.graphics.getWidth()).expandY().fillY();
		table.add(levels2).width(Gdx.graphics.getWidth()).expandY().fillY();
		table.add(levels3).width(Gdx.graphics.getWidth()).expandY().fillY();
		table.add(levels4).width(Gdx.graphics.getWidth()).expandY().fillY();
		
		ScrollPane scroll = new PickScrollPane(table, skin);
		container.add(scroll).expand().fill();
	}

	public void render () {
		Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
		stage.act(Gdx.graphics.getDeltaTime());
		stage.draw();
		Table.drawDebug(stage);
	}

	public void resize (int width, int height) {
		stage.setViewport(width, height, false);
	}

	public void dispose () {
		stage.dispose();
	}

	public boolean needsGL20 () {
		return false;
	}
	
	public ClickListener levelClickListener = new ClickListener() {
		@Override
		public void clicked (InputEvent event, float x, float y) {
			System.out.println("Click: " + event.getListenerActor().getName());
		}
	};
	
}