/*******************************************************************************
 * 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.graphics.g3d.decals;

import com.badlogic.gdx.graphics.glutils.ShaderProgram;
import com.badlogic.gdx.utils.Array;

/**
 * <p>
 * This class provides hooks which are invoked by {@link DecalBatch} to evaluate the group a sprite falls into, as well
 * as to adjust settings before and after rendering a group.
 * </p>
 * <p>
 * A group is identified by an integer. The {@link #beforeGroup(int, Array) beforeGroup()} method provides the strategy
 * with a list of all the decals, which are contained in the group itself, and will be rendered before the associated
 * call to {@link #afterGroup(int)}.<br/>
 * A call to {@code beforeGroup()} is always fallowed by a call to {@code afterGroup()}.<br/>
 * <b>Groups are always invoked based on their ascending int values</b>. Group -10 will be rendered before group -5,
 * group -5 before group 0, group 0 before group 6 and so on.<br/>
 * The call order for a single flush is always {@code beforeGroups(), beforeGroup1(), afterGroup1(), ... beforeGroupN(),
 * afterGroupN(), afterGroups()}.
 * </p>
 * <p>
 * The contents of the {@code beforeGroup()} call can be modified at will to realize view frustum culling, material &
 * depth sorting, ... all based on the requirements of the current group. The batch itself does not change OpenGL
 * settings except for whichever changes are entailed {@link DecalMaterial#set()}. If the group requires a special
 * shader, blending, {@link #getGroupShader(int)} should return it so that DecalBatch can apply it while rendering the
 * group.
 * </p>
 */
public interface GroupStrategy {
	/**
	 * Returns the shader to be used for the group. Can be null in which case the GroupStrategy doesn't support GLES 2.0
	 * 
	 * @param group
	 *            the group
	 * @return the {@link ShaderProgram}
	 */
	public ShaderProgram getGroupShader(int group);

	/**
	 * Assigns a group to a decal
	 * 
	 * @param decal
	 *            Decal to assign group to
	 * @return group assigned
	 */
	public int decideGroup(Decal decal);

	/**
	 * Invoked directly before rendering the contents of a group
	 * 
	 * @param group
	 *            Group that will be rendered
	 * @param contents
	 *            List of entries of arrays containing all the decals in the group
	 */
	public void beforeGroup(int group, Array<Decal> contents);

	/**
	 * Invoked directly after rendering of a group has completed
	 * 
	 * @param group
	 *            Group which completed rendering
	 */
	public void afterGroup(int group);

	/** Invoked before rendering any group */
	public void beforeGroups();

	/** Invoked after having rendered all groups */
	public void afterGroups();
}