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/*******************************************************************************
 * 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.Gdx;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;
import com.badlogic.gdx.utils.Array;
import com.badlogic.gdx.utils.Sort;

/** 
 * Minimalistic grouping strategy useful for orthogonal scenes where the camera faces the negative z axis. Handles enabling and
 * disabling of blending and uses world-z only front to back sorting for transparent decals.
 * 
 * 
 * States (* = any, EV = entry value - same as value before flush):

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 * expects exits on
glDepthMask true EV | true
GL_DEPTH_TEST enabled EV
glDepthFunc GL_LESS | GL_LEQUAL EV
GL_BLEND disabled EV | disabled
glBlendFunc * *
GL_TEXTURE_2D * disabled
 *  */
public class SimpleOrthoGroupStrategy implements GroupStrategy {
	private Comparator comparator = new Comparator();
	private static final int GROUP_OPAQUE = 0;
	private static final int GROUP_BLEND = 1;

	@Override
	public int decideGroup (Decal decal) {
		return decal.getMaterial().isOpaque() ? GROUP_OPAQUE : GROUP_BLEND;
	}

	@Override
	public void beforeGroup (int group, Array contents) {
		if (group == GROUP_BLEND) {
			Sort.instance().sort(contents, comparator);
			Gdx.gl10.glEnable(GL10.GL_BLEND);
			// no need for writing into the z buffer if transparent decals are the last thing to be rendered
			// and they are rendered back to front
			Gdx.gl10.glDepthMask(false);
		} else {
			// FIXME sort by material
		}
	}

	@Override
	public void afterGroup (int group) {
		if (group == GROUP_BLEND) {
			Gdx.gl10.glDepthMask(true);
			Gdx.gl10.glDisable(GL10.GL_BLEND);
		}
	}

	@Override
	public void beforeGroups () {
		Gdx.gl10.glEnable(GL10.GL_TEXTURE_2D);
	}

	@Override
	public void afterGroups () {
		Gdx.gl10.glDisable(GL10.GL_TEXTURE_2D);
	}

	class Comparator implements java.util.Comparator {
		@Override
		public int compare (Decal a, Decal b) {
			return a.getZ() - b.getZ() < 0 ? -1 : 1;
		}
	}

	@Override
	public ShaderProgram getGroupShader (int group) {
		return null;
	}
}

	expects	exits on
glDepthMask	true	EV \| true
GL_DEPTH_TEST	enabled	EV
glDepthFunc	GL_LESS \| GL_LEQUAL	EV
GL_BLEND	disabled	EV \| disabled
glBlendFunc	*	*
GL_TEXTURE_2D	*	disabled