/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkDepthPeelingPass.h

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

=========================================================================*/
// .NAME vtkDepthPeelingPass - Implement an Order Independent Transparency
// render pass.
// .SECTION Description
// Render the translucent polygonal geometry of a scene without sorting
// polygons in the view direction.
//
// This pass expects an initialized depth buffer and color buffer.
// Initialized buffers means they have been cleared with farest z-value and
// background color/gradient/transparent color.
// An opaque pass may have been performed right after the initialization.
//
// The depth peeling algorithm works by rendering the translucent polygonal
// geometry multiple times (once for each peel). The actually rendering of
// the translucent polygonal geometry is peformed by its delegate
// TranslucentPass. This delegate is therefore used multiple times.
//
// Its delegate is usually set to a vtkTranslucentPass.
// 
// .SECTION See Also
// vtkRenderPass, vtkTranslucentPass

#ifndef __vtkDepthPeelingPass_h
#define __vtkDepthPeelingPass_h

#include "vtkRenderPass.h"

class vtkOpenGLRenderWindow;
class vtkDepthPeelingPassLayerList; // Pimpl
class vtkShaderProgram2;
class vtkShader2;

class VTK_RENDERING_EXPORT vtkDepthPeelingPass : public vtkRenderPass
{
public:
  static vtkDepthPeelingPass *New();
  vtkTypeRevisionMacro(vtkDepthPeelingPass,vtkRenderPass);
  void PrintSelf(ostream& os, vtkIndent indent);

  // Description:
  // Perform rendering according to a render state \p s.
  // \pre s_exists: s!=0
  virtual void Render(const vtkRenderState *s);
  
  // Description:
  // Release graphics resources and ask components to release their own
  // resources.
  // \pre w_exists: w!=0
  void ReleaseGraphicsResources(vtkWindow *w);
  
  // Description:
  // Delegate for rendering the translucent polygonal geometry.
  // If it is NULL, nothing will be rendered and a warning will be emitted.
  // It is usually set to a vtkTranslucentPass.
  // Initial value is a NULL pointer.
  vtkGetObjectMacro(TranslucentPass,vtkRenderPass);
  virtual void SetTranslucentPass(vtkRenderPass *translucentPass);

  // Description:
  // In case of use of depth peeling technique for rendering translucent
  // material, define the threshold under which the algorithm stops to
  // iterate over peel layers. This is the ratio of the number of pixels
  // that have been touched by the last layer over the total number of pixels
  // of the viewport area.
  // Initial value is 0.0, meaning rendering have to be exact. Greater values
  // may speed-up the rendering with small impact on the quality.
  vtkSetClampMacro(OcclusionRatio,double,0.0,0.5);
  vtkGetMacro(OcclusionRatio,double);
  
  // Description:
  // In case of depth peeling, define the maximum number of peeling layers.
  // Initial value is 4. A special value of 0 means no maximum limit.
  // It has to be a positive value.
  vtkSetMacro(MaximumNumberOfPeels,int);
  vtkGetMacro(MaximumNumberOfPeels,int);

  // Description:
  // Tells if the last time this pass was executed, the depth peeling
  // algorithm was actually used. Initial value is false.
  vtkGetMacro(LastRenderingUsedDepthPeeling,bool);

  // Description:
  // Is rendering at translucent geometry stage using depth peeling and
  // rendering a layer other than the first one? (Boolean value)
  // If so, the uniform variables UseTexture and Texture can be set.
  // (Used by vtkOpenGLProperty or vtkOpenGLTexture)
  int GetDepthPeelingHigherLayer();
  
 protected:
  // Description:
  // Default constructor. TranslucentPass is set to NULL.
  vtkDepthPeelingPass();

  // Description:
  // Destructor.
  virtual ~vtkDepthPeelingPass();

  // Description:
  // Check if depth peeling is supported by the current OpenGL context.
  // \pre w_exists: w!=0
  void CheckSupport(vtkOpenGLRenderWindow *w);

  // Description:
  // Check the compilation status of some fragment shader source.
  void CheckCompilation(unsigned int fragmentShader);
  
  // Description:
  // Render a peel layer. If there is no more GPU RAM to save the texture,
  // return false otherwise returns true. Also if layer==0 and no prop have
  // been rendered (there is no translucent geometry), it returns false.
  // \pre s_exists: s!=0
  // \pre positive_layer: layer>=0
  int RenderPeel(const vtkRenderState *s,
                 int layer);

  vtkRenderPass *TranslucentPass;
  vtkTimeStamp CheckTime;
  bool IsChecked;
  bool IsSupported;

  // Description:
  // Cache viewport values for depth peeling.
  int ViewportX;
  int ViewportY;
  int ViewportWidth;
  int ViewportHeight;
  
  // Description:
  // Actual depth format: vtkgl::DEPTH_COMPONENT16_ARB
  // or vtkgl::DEPTH_COMPONENT24_ARB
  unsigned int DepthFormat;

  // Description:
  // In case of use of depth peeling technique for rendering translucent
  // material, define the threshold under which the algorithm stops to
  // iterate over peel layers. This is the ratio of the number of pixels
  // that have been touched by the last layer over the total number of pixels
  // of the viewport area.
  // Initial value is 0.0, meaning rendering have to be exact. Greater values
  // may speed-up the rendering with small impact on the quality.
  double OcclusionRatio;
   
  // Description:
  // In case of depth peeling, define the maximum number of peeling layers.
  // Initial value is 4. A special value of 0 means no maximum limit.
  // It has to be a positive value.
  int MaximumNumberOfPeels;

  bool LastRenderingUsedDepthPeeling;

  // Description:
  // Used by the depth peeling technique to store the transparency layers.
  vtkDepthPeelingPassLayerList *LayerList;
  
  unsigned int OpaqueLayerZ;
  unsigned int TransparentLayerZ;
//  unsigned int ProgramShader;

  // Is rendering at translucent geometry stage using depth peeling and
  // rendering a layer other than the first one? (Boolean value)
  // If so, the uniform variables UseTexture and Texture can be set.
  // (Used by vtkOpenGLProperty or vtkOpenGLTexture)
  int DepthPeelingHigherLayer;
  
  vtkShaderProgram2 *Prog;
  vtkShader2 *Shader;
  
  int ShadowTexUnit; // texture unit allocated for the shadow texture
  int OpaqueShadowTexUnit; // texture unit allocated for the opaque shadow tex.
  
 private:
  vtkDepthPeelingPass(const vtkDepthPeelingPass&);  // Not implemented.
  void operator=(const vtkDepthPeelingPass&);  // Not implemented.
};

#endif
