grass_parameters.h

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#ifndef GRASS_PARAMETERS_H
#define GRASS_PARAMETERS_H

#include <vrecko/ReaderWriter.h>
#include <gl/gl.h>
#include <vector>
#include <osg/Texture2D>

namespace grass
{

  // predeclaration
  class GrassCullCallback;


  // holds parameters of the Grass ability.
  struct GrassAbilityParameters : osg::Referenced
  {
  private:
    // copying of this object is not wanted
    GrassAbilityParameters(const GrassAbilityParameters &) {}

    // returns the half of width of "ideal" grass blade at y-position (bottom: y = 0.0f, top: y = 1.0f)
    inline float GrassBladeProfile(float y)
      { return 0.5f * (0.5f + y*y*(9.3f - y*(19.6f - 9.8f*y))); } // :)

    // creates a set of grassBlades within given context
    void CreateGrassBlades();

    // internal method which prepares both statesets
    void PrepareStateSets();

    // texture used for texturing blades of grass, far grass, and far soil
    osg::ref_ptr<osg::Texture2D> bladeTexture, farSoilTexture, farGrassTexture;

  public:
    // ensures that grass-blades are prepared
    void EnsureGrassBladesArePrepared()
    {
      if(grassBlades.size() == 0)
        CreateGrassBlades();
    }

    // only deletes display lists
    virtual ~GrassAbilityParameters()
    {
      for(int i = grassBlades.size(); i--; )
        glDeleteLists(grassBlades[i], 1);
    }

    // prepares everything for rendering grass
    void Init();
   
    // only sets default values
    GrassAbilityParameters();

    // use this method to read parameters from xml file
    bool loadXMLParameters(XERCES_CPP_NAMESPACE_QUALIFIER DOMNode *parametersNode);

    // use this to save parameters
    XERCES_CPP_NAMESPACE_QUALIFIER DOMNode *saveXMLParameters(XERCES_CPP_NAMESPACE_QUALIFIER DOMDocument *);

    // denstity of the grass (number of blades per unit area)
    float density;

    // range of random height, width and bend variance of blades
    float minHeight, maxHeight, minWidth, maxWidth, minBend, maxBend;

    // number of fractions of each grass blade. (low number means noticeably 'broken' blades,
    // but also a faster rendering) Optimum for good look depends also on bend intensity.
    // Nearly straight blades don't need to be divided into many pieces, while twisted ones need
    // a lot of pieces to look well. The minFractions value is applied to the straightest blades
    // and maxFractions to the most twisted ones. Others between them use adequate mix of those two values.
    int minFractions, maxFractions;

    // maximal size of a tringle which is covered with grass. Bigger triangles are divided
    // first and then covered. This rule should avoid need of drawind huge triangles covered with
    // grass which is in fact not visible at some far places of the triangle. Every smaller triangle
    // obtained by dividing bigger ones is a part of sometihng like an oct-tree, so the visibility
    // of its grass-cover can be determined quite efficiently.
    float maxArea;

    // maximal distance from grass blade to draw the grass blade
    float maxVisibility, minVisibility;

    // maximal difference between last LOD and current LOD to recreate a displaylist
    float maxLODdifference;

    // one divided by the difference between max and min Visibility
    float invVisibilityRange, visibilityRange;

    // a set of different grassBlades
    std::vector<GLuint> grassBlades;

    // two different statesets - one for low detail version of grass,
    // the other for detailed version of grass.
    osg::ref_ptr<osg::StateSet> lowDetailGrassStateSet;
    osg::ref_ptr<osg::StateSet> detailedGrassStateSet;

    // color used for far blades
    osg::Vec4 neutralColor;

    // CullCallback for GrassGeometry
    osg::ref_ptr<GrassCullCallback> grassCullCallback;
  };




}; // end of namespace grass

#endif // GRASS_PARAMETERS_H