/////////////////////////////////////////////////////////////////////////////
// showfacing.osl - color green for "frontfacing" (geometry where the 
//      normal faces the camera), red for "backfacing".  This is used
//      primarily for "debugging" geometry, searching for patches whose
//      normals face the wrong way.
//
/////////////////////////////////////////////////////////////////////////////
// Copyright 2004 NVIDIA Corporation.  All Rights Reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// 
// * Redistributions of source code must retain the above copyright
//   notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the
//   documentation and/or other materials provided with the distribution.
// * Neither the name of NVIDIA nor the names of its contributors
//   may be used to endorse or promote products derived from this software
//   without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// (This is the Modified BSD License)
/////////////////////////////////////////////////////////////////////////////

surface
showfacing
    [[ string description = "Visualize the orientation of surfaces - frontfacing green, backfacing red" ]]
(
    float Ka = 0.25
        [[  string description = "Non-directional brightness",
            float UIsoftmin = 0, float UIsoftmax = 1 ]],
    float Kd = 0.75
        [[  string description = "Directional brightness",
            float UIsoftmin = 0, float UIsoftmax = 1 ]]
  )
{
    // Compute the dot product between I and N (-1 for surfaces
    // exactly facing the camera, 0 for those perpendicular, 1 for
    // those facing exactly away from camera)
    float d = dot (normalize(I), normalize(N));

    // Color based on the dot product of N and I -- green for < 0, red for >0 
    C = mix (color(0,1,0), color(1,0,0), step(0,d));

    // Also scale the intensity based on orientation, so we can see the shape
    // of objects.
    C *= (Ka + Kd * d*d);
    opacity = 1;
}
