/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// Copyright (c) 2004-2005 Lutz Latta
//
// 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.


// Supporting functions for adapting generic sorting algorithm to distance sorting.
//
// Note: Packing of two 16-bit halfs into one float is used.
// This works only perfect with texture sizes up to 1024.
// With size 2048 the higher coordinates shift from xxxx.5 to integer values,
// then the algorithm should be changed to store only integers and always add 0.5.
#define USE_RGB_FORMAT
#ifndef USE_RGB_FORMAT
float2 initSortIndex(float2 sortIndex : TEXCOORD0) : COLOR
{
    // TBD...
    return float2(0, pack_2half(sortIndex));
    //return float2(sortIndex.x, sortIndex.y);
}

float2 computeDistance(float2 texCoord : TEXCOORD0,
                       uniform samplerRECT sortTexture : register(s0),
                       uniform samplerRECT positionTexture : register(s1),
                       uniform float3 viewerPosition) : COLOR
{
    float sortIndex = texRECT(sortTexture, texCoord.xy).y;
    half2 particleIndex = unpack_2half(sortIndex);

    float3 particlePos = (float3)texRECT(positionTexture, particleIndex);
	
    float3 delta = viewerPosition - particlePos;
    float distanceSqr = dot(delta, delta);

    // Prevent unused, far-away particles from destroying comparisons in sorting.
    if (distanceSqr > 1e6 || isnan(distanceSqr))
        distanceSqr = 1e6;

    return float2(distanceSqr, sortIndex);
}
float4 lookupPosition(float2 texCoord : TEXCOORD0,
                      uniform samplerRECT sortTexture : register(s0),
                      uniform samplerRECT positionTexture : register(s1)) : COLOR
{
    float sortIndex = texRECT(sortTexture, texCoord.xy).y;
    half2 particleIndex = unpack_2half(sortIndex);
    float4 particlePos = (float4)texRECT(positionTexture, particleIndex);

    return particlePos;
}

#else
float3 initSortIndex(float2 sortIndex : TEXCOORD0) : COLOR
{
    //return float3(0, sortIndex.x, sortIndex.y);
    return float3(1e6, sortIndex.x, sortIndex.y);
}

float3 computeDistance(float2 texCoord : TEXCOORD0,
                       uniform samplerRECT sortTexture : register(s0),
                       uniform samplerRECT positionTexture : register(s1),
                       uniform float3 viewerPosition) : COLOR
{
    float2 particleIndex = texRECT(sortTexture, texCoord.xy).yz;
    float3 particlePos = texRECT(positionTexture, particleIndex).xyz;

    float3 delta = viewerPosition - particlePos;
    float distanceSqr = dot(delta, delta);

    // Prevent unused, far-away particles from destroying comparisons in sorting.
    if (distanceSqr > 1e6 || isnan(distanceSqr))
        distanceSqr = 1e6;

    return float3(distanceSqr, particleIndex.x, particleIndex.y);
}

float3 lookupPosition(float2 texCoord : TEXCOORD0,
                      uniform samplerRECT sortTexture : register(s0),
                      uniform samplerRECT positionTexture : register(s1)) : COLOR
{
    float2 particleIndex = texRECT(sortTexture, texCoord.xy).yz;
    float3 particlePos = texRECT(positionTexture, particleIndex).xyz;

    return particlePos;
}
#endif