/*
 * Copyright (C) 2017 Open Source Robotics Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
*/

// Code in this file has been adapted from Ogre. The original Ogre's licence and
// copyright headers are copied below:

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
(Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org

Copyright (c) 2000-2012 Torus Knot Software Ltd
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.
-----------------------------------------------------------------------------
*/
//-----------------------------------------------------------------------------
// Program Name: SGXLib_IntegratedPSSM
// Program Desc: Integrated PSSM functions.
// Program Type: Vertex/Pixel shader
// Language: GLSL
//-----------------------------------------------------------------------------

//-----------------------------------------------------------------------------
void SGX_CopyDepth(in vec4 clipSpacePos,
			 out float oDepth)
{
	oDepth = clipSpacePos.z;
}

//-----------------------------------------------------------------------------
void SGX_ModulateScalar(in float vIn0, in vec4 vIn1, out vec4 vOut)
{
	vOut = vIn0 * vIn1;
}

//-----------------------------------------------------------------------------
void SGX_ApplyShadowFactor_Diffuse(in vec4 ambient,
					  in vec4 lightSum,
					  in float fShadowFactor,
					  out vec4 oLight)
{
	oLight.rgb = ambient.rgb + (lightSum.rgb - ambient.rgb) * (fShadowFactor);
	oLight.a   = lightSum.a;
}

//-----------------------------------------------------------------------------
float _SGX_ShadowPoisson9(sampler2DShadow shadowMap, vec4 shadowMapPos, vec2 invShadowMapSize, bool hardwarePCF)
{
  // Remove shadow outside shadow maps so that all that area appears lit
  if (shadowMapPos.z < 0.0 || shadowMapPos.z > 1.0)
    return 1.0;

  float shadow = 0.0;

  // 9-sample poisson disk blur
  vec2 poissonDisk[9] = vec2[](
    vec2( 0.0, 0.0 ),
    vec2( -0.987, 0.127 ),
    vec2( -0.168, -0.924 ),
    vec2( 0.637, 0.633 ),
    vec2( 0.888, -0.296 ),
    vec2( 0.516, 0.0664 ),
    vec2( -0.408, -0.332 ),
    vec2( -0.491, 0.263 ),
    vec2( 0.061, 0.851 )
  );

  for (int i = 0; i < 9; i++)
  {
    vec4 newUV = shadowMapPos;
    newUV.xy += poissonDisk[i] * invShadowMapSize;
    // Divide by w necessary for LiSPMS, which is no longer in use
    // newUV = newUV / newUV.w;
    // This texture() does the depth compare and provides Hardware PCF as a
    // driver hack.
    // shadow += shadow2D(shadowMap, newUV.xyz).r;
    float d = shadow2D(shadowMap, newUV.xyz).r;
    if (hardwarePCF)
      shadow += d;
    else
      shadow += step(shadowMapPos.z, d);
  }
  shadow /= 9.0;

  // smoothstep makes shadow edges appear more crisp and hides Mach bands
  float s = smoothstep(0.0, 1.0, shadow);
  // make shadow lighter color
  float minShadowFactor = 0.2;
  s = s * (1.0 - minShadowFactor) + minShadowFactor;
  return s;
}

//-----------------------------------------------------------------------------
void SGX_ComputeShadowFactor_PSSM3(in float fDepth,
							in vec4 vSplitPoints,
							in vec4 lightPosition0,
							in vec4 lightPosition1,
							in vec4 lightPosition2,
							in sampler2DShadow shadowMap0,
							in sampler2DShadow shadowMap1,
							in sampler2DShadow shadowMap2,
							in vec4 invShadowMapSize0,
							in vec4 invShadowMapSize1,
							in vec4 invShadowMapSize2,
							out float oShadowFactor)
{
  // hack! On OSX the shadow map size is halved so we use this as a hint
  // that hardware PCF is not enabled.
  bool hardwarePCF = false;
  if (invShadowMapSize0.x == invShadowMapSize1.x)
    hardwarePCF = true;

  if (fDepth  <= vSplitPoints.x)
  {
    oShadowFactor =
      _SGX_ShadowPoisson9(shadowMap0, lightPosition0, invShadowMapSize0.xy, hardwarePCF);
  }
  else if (fDepth <= vSplitPoints.y)
  {
    oShadowFactor =
      _SGX_ShadowPoisson9(shadowMap1, lightPosition1, invShadowMapSize1.xy, hardwarePCF);
  }
  else
  {
    oShadowFactor =
      _SGX_ShadowPoisson9(shadowMap2, lightPosition2, invShadowMapSize2.xy, hardwarePCF);
  }
}
