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/****************************************************************************
Copyright 2004, Colorado School of Mines and others.
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 edu.mines.jtk.sgl;

/**
 * OpenGL state, a collection of OpenGL state attributes.
 * 
 * Nodes in a scene graph can set OpenGL attributes by calling OpenGL 
 * functions explicitly. Alternatively, these attributes can be set by 
 * applying a state class that implements this interface. This second 
 * alternative offers two advantages.
 * 

 * First, classes that implement this interface define standard collections 
 * of OpenGL state attributes, with a convenient interface for getting and 
 * setting those attributes. For example, color attributes can be set by 
 * passing a {@link java.awt.Color}.
 * 

 * Second, states can be associated with nodes and shared among multiple 
 * nodes in a scene graph. Then, changes to any state's attributes are 
 * reflected in all nodes that share that state.
 * 

 * Classes that implement this interface have fields that correspond to 
 * OpenGL state attributes. States have methods that set and unset the 
 * values of these attribute fields. A state applies itself by calling 
 * relevant OpenGL functions for all attribute fields that are set. A 
 * state does not call OpenGL functions for fields that are not set.
 * 
 * States also have methods that determine whether or not an attribute 
 * field has been set and methods that get the values of a field. For 
 * attribute fields not set, these get methods return OpenGL default 
 * values.
 * @author Dave Hale, Colorado School of Mines
 * @version 2005.05.31
 */
public interface State {

  /**
   * Applies this OpenGL state. This method makes OpenGL state consistent 
   * with any attribute fields in this state that are currently set.
   */
  public void apply();

  /**
   * Gets the OpenGL attribute bits for this state. 
   * These bits indicate what OpenGL state is changed by the method 
   * {@link #apply()}. If these bits are passed to glPushAttrib before 
   * calling {@link #apply()}, then glPopAttrib will restore any OpenGL 
   * state that is changed by that method.
   */
  public int getAttributeBits();
}