/*******************************************************************************
 * 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;

import com.badlogic.gdx.graphics.VertexAttributes.Usage;
import com.badlogic.gdx.graphics.glutils.ShaderProgram;

/** A single vertex attribute defined by its {@link Usage}, its number of components and its shader alias. The Usage is needed for
 * the fixed function pipeline of OpenGL ES 1.x. Generic attributes are not supported in the fixed function pipeline. The number
 * of components defines how many components the attribute has. The alias defines to which shader attribute this attribute should
 * bind. The alias is used by a {@link Mesh} when drawing with a {@link ShaderProgram}. The alias can be changed at any time.
 * 
 * @author mzechner */
public final class VertexAttribute {
	/** the attribute {@link Usage} **/
	public final int usage;
	/** the number of components this attribute has **/
	public final int numComponents;
	/** the offset of this attribute in bytes, don't change this! **/
	public int offset;
	/** the alias for the attribute used in a {@link ShaderProgram} **/
	public String alias;
	/** optional unit/index specifier, used for texture coordinates and bone weights **/
	public int unit;
	private final int usageIndex;

	/** Constructs a new VertexAttribute.
	 * 
	 * @param usage the usage, used for the fixed function pipeline. Generic attributes are not supported in the fixed function
	 *           pipeline.
	 * @param numComponents the number of components of this attribute, must be between 1 and 4.
	 * @param alias the alias used in a shader for this attribute. Can be changed after construction. */
	public VertexAttribute (int usage, int numComponents, String alias) {
		this(usage, numComponents, alias, 0);
	}
	
	/** Constructs a new VertexAttribute.
	 * 
	 * @param usage the usage, used for the fixed function pipeline. Generic attributes are not supported in the fixed function
	 *           pipeline.
	 * @param numComponents the number of components of this attribute, must be between 1 and 4.
	 * @param alias the alias used in a shader for this attribute. Can be changed after construction.
	 * @param index unit/index of the attribute, used for boneweights and texture coordinates. 
	 * */
	public VertexAttribute (int usage, int numComponents, String alias, int index) {
		this.usage = usage;
		this.numComponents = numComponents;
		this.alias = alias;
		this.unit = index;
		this.usageIndex = Integer.numberOfTrailingZeros(usage);
	}

	public static VertexAttribute Position () {
		return new VertexAttribute(Usage.Position, 3, ShaderProgram.POSITION_ATTRIBUTE);
	}

	public static VertexAttribute TexCoords (int unit) {
		return new VertexAttribute(Usage.TextureCoordinates, 2, ShaderProgram.TEXCOORD_ATTRIBUTE + unit, unit);
	}

	public static VertexAttribute Normal () {
		return new VertexAttribute(Usage.Normal, 3, ShaderProgram.NORMAL_ATTRIBUTE);
	}

	public static VertexAttribute Color () {
		return new VertexAttribute(Usage.ColorPacked, 4, ShaderProgram.COLOR_ATTRIBUTE);
	}

	public static VertexAttribute ColorUnpacked () {
		return new VertexAttribute(Usage.Color, 4, ShaderProgram.COLOR_ATTRIBUTE);
	}
	
	public static VertexAttribute Tangent() {
		return new VertexAttribute(Usage.Tangent, 3, ShaderProgram.TANGENT_ATTRIBUTE);
	}
	
	public static VertexAttribute Binormal() {
		return new VertexAttribute(Usage.BiNormal, 3, ShaderProgram.BINORMAL_ATTRIBUTE);
	}
	
	public static VertexAttribute BoneWeight (int unit) {
		return new VertexAttribute(Usage.BoneWeight, 2, "a_boneWeight" + unit, unit);
	}

	/** Tests to determine if the passed object was created with the same parameters */
	@Override
	public boolean equals (final Object obj) {
		if (!(obj instanceof VertexAttribute)) {
			return false;
		}
		return equals((VertexAttribute)obj);
	}
	
	public boolean equals (final VertexAttribute other) {
		return other != null && usage == other.usage && numComponents == other.numComponents && alias.equals(other.alias) && unit == other.unit; 
	}
	
	/** @return A unique number specifying the usage index (3 MSB) and unit (1 LSB). */ 
	public int getKey() {
		return (usageIndex << 8) + (unit & 0xFF);
	}
}
