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

  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.

=========================================================================*/
/**
 * @class   vtkDepthPeelingPass
 * @brief   Implement an Order Independent Transparency
 * render pass.
 *
 * 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 performed by its delegate
 * TranslucentPass. This delegate is therefore used multiple times.
 *
 * Its delegate is usually set to a vtkTranslucentPass.
 *
 * @sa
 * vtkRenderPass, vtkTranslucentPass
*/

#ifndef vtkDepthPeelingPass_h
#define vtkDepthPeelingPass_h

#include "vtkRenderingOpenGLModule.h" // For export macro
#include "vtkRenderPass.h"

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

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

  /**
   * Perform rendering according to a render state \p s.
   * \pre s_exists: s!=0
   */
  void Render(const vtkRenderState *s) override;

  /**
   * Release graphics resources and ask components to release their own
   * resources.
   * \pre w_exists: w!=0
   */
  void ReleaseGraphicsResources(vtkWindow *w) override;

  //@{
  /**
   * 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);
  //@}

  //@{
  /**
   * 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);
  //@}

  //@{
  /**
   * 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);
  //@}

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

  /**
   * 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:
  /**
   * Default constructor. TranslucentPass is set to NULL.
   */
  vtkDepthPeelingPass();

  /**
   * Destructor.
   */
  ~vtkDepthPeelingPass() override;

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

  /**
   * Check the compilation status of some fragment shader source.
   */
  void CheckCompilation(unsigned int fragmentShader);

  /**
   * 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;

  //@{
  /**
   * Cache viewport values for depth peeling.
   */
  int ViewportX;
  int ViewportY;
  int ViewportWidth;
  int ViewportHeight;
  //@}

  /**
   * Actual depth format: vtkgl::DEPTH_COMPONENT16_ARB
   * or vtkgl::DEPTH_COMPONENT24_ARB
   */
  unsigned int DepthFormat;

  /**
   * 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;

  /**
   * 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;

  /**
   * 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&) = delete;
  void operator=(const vtkDepthPeelingPass&) = delete;
};

#endif