/////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2009-2010 Sony Pictures Imageworks Inc., et al.  All Rights Reserved.
//
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// modification, are permitted provided that the following conditions are
// met:
// * Redistributions of source code must retain the above copyright
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// * Redistributions in binary form must reproduce the above copyright
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//   this software without specific prior written permission.
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/////////////////////////////////////////////////////////////////////////////


#ifndef CCL_OSLUTIL_H
#define CCL_OSLUTIL_H

// Return wireframe opacity factor [0, 1] given a geometry type in
// ("triangles", "polygons" or "patches"), and a line_width in raster
// or world space depending on the last (raster) boolean argument.
//
float wireframe(string edge_type, float line_width, int raster)
{
   // ray differentials are so big in diffuse context that this function would always return "wire"
   if (raytype("path:diffuse")) return 0.0;

   int np = 0;
   point p[64];
   float pixelWidth = 1;

   if (edge_type == "triangles")
   {
      np = 3;
      if (!getattribute("geom:trianglevertices", p))
         return 0.0;
   }
   else if (edge_type == "polygons" || edge_type == "patches")
   {
      getattribute("geom:numpolyvertices", np);
      if (np < 3 || !getattribute("geom:polyvertices", p))
         return 0.0;
   }

   if (raster)
   {
      // Project the derivatives of P to the viewing plane defined
      // by I so we have a measure of how big is a pixel at this point
      float pixelWidthX = length(Dx(P) - dot(Dx(P), I) * I);
      float pixelWidthY = length(Dy(P) - dot(Dy(P), I) * I);
      // Take the average of both axis' length
      pixelWidth = (pixelWidthX + pixelWidthY) / 2;
   }

   // Use half the width as the neighbor face will render the
   // other half. And take the square for fast comparison
   pixelWidth *= 0.5 * line_width;
   pixelWidth *= pixelWidth;
   for (int i = 0; i < np; i++)
   {
      int i2 = i ? i - 1 : np - 1;
      vector dir = P - p[i];
      vector edge = p[i] - p[i2];
      vector crs = cross(edge, dir);
      // At this point dot(crs, crs) / dot(edge, edge) is
      // the square of area / length(edge) == square of the
      // distance to the edge.
      if (dot(crs, crs) < (dot(edge, edge) * pixelWidth))
         return 1;
   }
   return 0;
}

float wireframe(string edge_type, float line_width) { return wireframe(edge_type, line_width, 1); }
float wireframe(string edge_type) { return wireframe(edge_type, 1.0, 1); }
float wireframe() { return wireframe("polygons", 1.0, 1); }

#endif /* CCL_OSLUTIL_H */