GLHardwareOcclusionQuery.cs :  » Game » RealmForge » Axiom » RenderSystems » OpenGL » C# / CSharp Open Source

#region LGPL License
/*
Axiom Game Engine Library
Copyright (C) 2003  Axiom Project Team

The overall design, and a majority of the core engine and rendering code 
contained within this library is a derivative of the open source Object Oriented 
Graphics Engine OGRE, which can be found at http://ogre.sourceforge.net.  
Many thanks to the OGRE team for maintaining such a high quality project.

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#endregion

using System;
using Axiom.Core;
using Axiom.Graphics;
using Tao.OpenGl;

namespace Axiom.RenderSystems.OpenGL{
  /// <summary>
  /// Summary description for GLHardwareOcclusionQuery.
  /// </summary>
  public class GLHardwareOcclusionQuery : IHardwareOcclusionQuery {
    /// <summary>
    ///    Number of fragments returned from the last query.
    /// </summary>
    private int lastFragmentCount;
    /// <summary>
    ///    Flag that indicates whether hardware queries are supported
    /// </summary>
    private bool isSupported;
    /// <summary>
    ///    Rate at which queries are skipped (in frames).
    /// </summary>
    private int skipRate;
    /// <summary>
    ///    Current count of number of skipped frames since query last ran.
    /// </summary>
    private int skipCounter;
    /// <summary>
    ///    Id of the GL query.
    /// </summary>
    private int id;
    
    public GLHardwareOcclusionQuery() {
      isSupported = Root.Instance.RenderSystem.Caps.CheckCap(Capabilities.HardwareOcculusion);

      if(isSupported) {
        Gl.glGenOcclusionQueriesNV(1, out id);
      }
    }

    #region IHardwareOcclusionQuery Members

    public void Begin() {
      // proceed if supported, or silently fail otherwise
      if(isSupported) {
        if(skipCounter == skipRate) {
          skipCounter = 0;
        }

        if(skipCounter == 0) { // && lastFragmentCount != 0) {
          Gl.glBeginOcclusionQueryNV(id);
        }
      }
    }

    public int PullResults(bool flush) {
      // note: flush doesn't apply to GL

      // default to returning a high count.  will be set otherwise if the query runs
      lastFragmentCount = 100000;

      if(isSupported) {
        Gl.glGetOcclusionQueryivNV(id, Gl.GL_PIXEL_COUNT_NV, out lastFragmentCount);
      }
        
      return lastFragmentCount;
    }

    public void End() {
      // proceed if supported, or silently fail otherwise
      if(isSupported) {
        if(skipCounter == 0) { // && lastFragmentCount != 0) {
          Gl.glEndOcclusionQueryNV();
        }

        skipCounter++;
      }
    }

    public int SkipRate {
      get {
        return skipRate;
      }
      set {
        skipRate = value;
      }
    }

    public int LastFragmentCount {
      get {
        return lastFragmentCount;
      }
    }

    #endregion
  }
}