// Copyright 2016 Activision Publishing, Inc.
// 
// Permission is hereby granted, free of charge, to any person obtaining 
// a copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation 
// the rights to use, copy, modify, merge, publish, distribute, sublicense, 
// and/or sell copies of the Software, and to permit persons to whom the Software 
// is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all 
// copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 
// SOFTWARE.

#define BASE_RESOLUTION 128
#define PROBE_REFLECTION_MIPS 7
#define PROBE_REFLECTION_MIPS_FULL 8

float R_SpecParamFromGloss( float gloss )
{
	const float GGX_MAX_SPEC_POWER = 18;
	float exponent = powf( 2.0f, gloss * GGX_MAX_SPEC_POWER );
	// returns roughness == sqrt(alpha) for GGX physically-based shader
	return powf( 2.0f / ( 1 + exponent ), .25f );
}

void create_cubemap_level_params(vector<CubemapLevelParams> &level_params)
{
	for (int mip = 0; mip < PROBE_REFLECTION_MIPS; ++mip)
	{
		const float ENVMAP_MIPLEVEL_0_PB = 6.0f;
		const float ENVMAP_MIPLEVEL_1_PB = 0.0f;

		level_params[mip].level = mip;
		level_params[mip].gloss = (ENVMAP_MIPLEVEL_0_PB - mip) / (ENVMAP_MIPLEVEL_0_PB - ENVMAP_MIPLEVEL_1_PB);
		level_params[mip].roughness = R_SpecParamFromGloss(level_params[mip].gloss);
		level_params[mip].res = BASE_RESOLUTION >> mip;
	}
}