-- glslfx version 0.1

//
// Copyright 2016 Pixar
//
// Licensed under the Apache License, Version 2.0 (the "Apache License")
// with the following modification; you may not use this file except in
// compliance with the Apache License and the following modification to it:
// Section 6. Trademarks. is deleted and replaced with:
//
// 6. Trademarks. This License does not grant permission to use the trade
//    names, trademarks, service marks, or product names of the Licensor
//    and its affiliates, except as required to comply with Section 4(c) of
//    the License and to reproduce the content of the NOTICE file.
//
// You may obtain a copy of the Apache License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Apache License with the above modification is
// distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the Apache License for the specific
// language governing permissions and limitations under the Apache License.
//

--- This is what an import might look like.
--- #import $TOOLS/hdSt/shaders/fallbackLighting.glslfx

--- --------------------------------------------------------------------------
-- glsl Fallback.LightIntegrator
#ifndef HD_HAS_integrateLights
#define HD_HAS_integrateLights
#endif

struct LightingContribution {
    vec3 diffuse;
};

struct LightingInterfaceProperties {
    float unused;
};

LightingContribution
integrateLightsDefault(vec4 Peye, vec3 Neye, LightingInterfaceProperties props)
{
    vec3 n = normalize(Neye);

    LightingContribution result;
    result.diffuse = vec3(dot(n, vec3(0,0,1)));

    return result;
}

LightingContribution
integrateLightsConstant(vec4 Peye, vec3 Neye, LightingInterfaceProperties props)
{
    LightingContribution result;
    //pefectly diffuse white hemisphere contribution
    result.diffuse = vec3(1);

    return result;
}

-- glsl Fallback.Lighting

LightingContribution
integrateLights(vec4 Peye, vec3 Neye, LightingInterfaceProperties props);

vec3 FallbackLighting(in vec3 Peye, in vec3 Neye, in vec3 color)
{
    LightingInterfaceProperties props;
    LightingContribution light = integrateLights(vec4(Peye, 1), Neye, props);
    return color * light.diffuse;
}