source: nanovis/trunk/shaders/distancesort.cg @ 5722

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

float2 initSortIndex(float2 _SortIndex : TEXCOORD0) : COLOR
{
    return float2(0, pack_2half(_SortIndex));
}

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;
}