#include "fluid_common.hlsli"

#define Texture_phi_n Texture_color
#define Texture_phi_n_hat Texture_tempscalar

//	Advect MCCormack

//	Pixel
float4 main(p_fluidsim input) : SV_Target
{
    if (IsNonEmptyCell(input.texcoords.xyz))
    {
        return 0;
    }

    // get advected new position
    float3 npos = input.cell0 - timestep * forward *
        Texture_velocity0.SampleLevel(samPointClamp, input.texcoords, 0).xyz;

    // convert new position to texture coordinates
    float3 nposTC = float3(npos.x / textureWidth, npos.y / textureHeight, (npos.z + 0.5) / textureDepth);

    // find the texel corner closest to the semi-Lagrangian "particle"
    float3 nposTexel = floor(npos + float3(0.5f, 0.5f, 0.5f));
    float3 nposTexelTC = float3(nposTexel.x / textureWidth, nposTexel.y / textureHeight, (nposTexel.z + 0.5) / textureDepth);

    // ht (float-texel)
    float3 ht = float3(0.5f / textureWidth, 0.5f / textureHeight, 0.5f / textureDepth);

    // get the values of nodes that contribute to the interpolated value
    // (texel centers are at float-integer locations)
    float4 nodeValues[8];
    nodeValues[0] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(-ht.x, -ht.y, -ht.z), 0);
    nodeValues[1] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(-ht.x, -ht.y, ht.z), 0);
    nodeValues[2] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(-ht.x, ht.y, -ht.z), 0);
    nodeValues[3] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(-ht.x, ht.y, ht.z), 0);
    nodeValues[4] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(ht.x, -ht.y, -ht.z), 0);
    nodeValues[5] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(ht.x, -ht.y, ht.z), 0);
    nodeValues[6] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(ht.x, ht.y, -ht.z), 0);
    nodeValues[7] = Texture_phi_n.SampleLevel(samPointClamp, nposTexelTC + float3(ht.x, ht.y, ht.z), 0);

    // determine a valid range for the result
    float4 phiMin = min(min(min(nodeValues[0], nodeValues[1]), nodeValues[2]), nodeValues[3]);
    phiMin = min(min(min(min(phiMin, nodeValues[4]), nodeValues[5]), nodeValues[6]), nodeValues[7]);

    float4 phiMax = max(max(max(nodeValues[0], nodeValues[1]), nodeValues[2]), nodeValues[3]);
    phiMax = max(max(max(max(phiMax, nodeValues[4]), nodeValues[5]), nodeValues[6]), nodeValues[7]);

    float4 r;
    // Perform final MACCORMACK advection step:
    // You can use point sampling and keep Texture_phi_n_1_hat
    //  r = Texture_phi_n_1_hat.SampleLevel( samPointClamp, input.texcoords, 0 )
    // OR use bilerp to avoid the need to keep a separate texture for phi_n_1_hat
    r = Texture_phi_n.SampleLevel(samLinear, nposTC, 0) + 0.5 * (Texture_phi_n.SampleLevel(samPointClamp, input.texcoords, 0) -
        Texture_phi_n_hat.SampleLevel(samPointClamp, input.texcoords, 0));

    // clamp result to the desired range
    r = max(min(r, phiMax), phiMin);

    float4 ret = r * modulate - k;
    ret = clamp(ret, float4(0, 0, 0, 0), float4(5, 5, 5, 5));
    return ret;
}