WidgetGroup.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.scenes.scene2d.ui;

import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.scenes.scene2d.Actor;
import com.badlogic.gdx.scenes.scene2d.Group;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.utils.Layout;
import com.badlogic.gdx.utils.SnapshotArray;

/**
 * A {@link Group} that participates in layout and provides a minimum, preferred, and maximum size.
 * <p>
 * The default preferred size of a widget group is 0 and this is almost always overridden by a subclass. The default
 * minimum size returns the preferred size, so a subclass may choose to return 0 for minimum size if it wants to allow
 * itself to be sized smaller than the preferred size. The default maximum size is 0, which means no maximum size.
 * <p>
 * See {@link Layout} for details on how a widget group should participate in layout. A widget group's mutator methods
 * should call {@link #invalidate()} or {@link #invalidateHierarchy()} as needed. By default, invalidateHierarchy is
 * called when child widgets are added and removed.
 * 
 * @author Nathan Sweet
 */
public class WidgetGroup extends Group implements Layout {
	private boolean needsLayout = true;
	private boolean fillParent;
	private boolean layoutEnabled = true;

	public float getMinWidth() {
		return getPrefWidth();
	}

	public float getMinHeight() {
		return getPrefHeight();
	}

	public float getPrefWidth() {
		return 0;
	}

	public float getPrefHeight() {
		return 0;
	}

	public float getMaxWidth() {
		return 0;
	}

	public float getMaxHeight() {
		return 0;
	}

	public void setLayoutEnabled(boolean enabled) {
		if (layoutEnabled == enabled)
			return;
		layoutEnabled = enabled;
		setLayoutEnabled(this, enabled);
	}

	private void setLayoutEnabled(Group parent, boolean enabled) {
		SnapshotArray<Actor> children = getChildren();
		for (int i = 0, n = children.size; i < n; i++) {
			Actor actor = children.get(i);
			if (actor instanceof Layout)
				((Layout) actor).setLayoutEnabled(enabled);
			else if (actor instanceof Group) //
				setLayoutEnabled((Group) actor, enabled);
		}
	}

	public void validate() {
		if (!layoutEnabled)
			return;
		Group parent = getParent();
		if (fillParent && parent != null) {
			Stage stage = getStage();

			float parentWidth, parentHeight;
			if (stage != null && parent == stage.getRoot()) {
				parentWidth = stage.getWidth();
				parentHeight = stage.getHeight();
			} else {
				parentWidth = parent.getWidth();
				parentHeight = parent.getHeight();
			}
			if (getWidth() != parentWidth || getHeight() != parentHeight) {
				setWidth(parentWidth);
				setHeight(parentHeight);
				invalidate();
			}
		}

		if (!needsLayout)
			return;
		needsLayout = false;
		layout();
	}

	/** Returns true if the widget's layout has been {@link #invalidate() invalidated}. */
	public boolean needsLayout() {
		return needsLayout;
	}

	public void invalidate() {
		needsLayout = true;
	}

	public void invalidateHierarchy() {
		invalidate();
		Group parent = getParent();
		if (parent instanceof Layout)
			((Layout) parent).invalidateHierarchy();
	}

	protected void childrenChanged() {
		invalidateHierarchy();
	}

	public void pack() {
		float newWidth = getPrefWidth();
		float newHeight = getPrefHeight();
		if (newWidth != getWidth() || newHeight != getHeight()) {
			setWidth(newWidth);
			setHeight(newHeight);
			invalidate();
		}
		validate();
	}

	public void setFillParent(boolean fillParent) {
		this.fillParent = fillParent;
	}

	public void layout() {
	}

	/**
	 * If this method is overridden, the super method or {@link #validate()} should be called to ensure the widget group
	 * is laid out.
	 */
	public void draw(SpriteBatch batch, float parentAlpha) {
		validate();
		super.draw(batch, parentAlpha);
	}
}