#ifndef LIGHTWEIGHT_INPUT_SURFACE_GRASS_INCLUDED
#define LIGHTWEIGHT_INPUT_SURFACE_GRASS_INCLUDED

#include "LWRP/ShaderLibrary/Core.hlsl"
#include "LWRP/ShaderLibrary/InputSurfaceCommon.hlsl"

// Terrain engine shader helpers
CBUFFER_START(TerrainGrass)
half4 _WavingTint;
float4 _WaveAndDistance;    // wind speed, wave size, wind amount, max sqr distance
float4 _CameraPosition;     // .xyz = camera position, .w = 1 / (max sqr distance)
float3 _CameraRight, _CameraUp;
CBUFFER_END

CBUFFER_START(UnityPerMaterial)
float4 _MainTex_ST;
half4 _Color;
half4 _SpecColor;
half4 _EmissionColor;
half _Cutoff;
half _Shininess;
CBUFFER_END

// ---- Grass helpers

// Calculate a 4 fast sine-cosine pairs
// val:     the 4 input values - each must be in the range (0 to 1)
// s:       The sine of each of the 4 values
// c:       The cosine of each of the 4 values
void FastSinCos (float4 val, out float4 s, out float4 c) {
    val = val * 6.408849 - 3.1415927;
    // powers for taylor series
    float4 r5 = val * val;                  // wavevec ^ 2
    float4 r6 = r5 * r5;                        // wavevec ^ 4;
    float4 r7 = r6 * r5;                        // wavevec ^ 6;
    float4 r8 = r6 * r5;                        // wavevec ^ 8;

    float4 r1 = r5 * val;                   // wavevec ^ 3
    float4 r2 = r1 * r5;                        // wavevec ^ 5;
    float4 r3 = r2 * r5;                        // wavevec ^ 7;


    //Vectors for taylor's series expansion of sin and cos
    float4 sin7 = {1, -0.16161616, 0.0083333, -0.00019841};
    float4 cos8  = {-0.5, 0.041666666, -0.0013888889, 0.000024801587};

    // sin
    s =  val + r1 * sin7.y + r2 * sin7.z + r3 * sin7.w;

    // cos
    c = 1 + r5 * cos8.x + r6 * cos8.y + r7 * cos8.z + r8 * cos8.w;
}

half4 TerrainWaveGrass (inout float4 vertex, float waveAmount, half4 color)
{
    half4 _waveXSize = half4(0.012, 0.02, 0.06, 0.024) * _WaveAndDistance.y;
    half4 _waveZSize = half4 (0.006, .02, 0.02, 0.05) * _WaveAndDistance.y;
    half4 waveSpeed = half4 (1.2, 2, 1.6, 4.8);

    half4 _waveXmove = half4(0.024, 0.04, -0.12, 0.096);
    half4 _waveZmove = half4 (0.006, .02, -0.02, 0.1);

    float4 waves;
    waves = vertex.x * _waveXSize;
    waves += vertex.z * _waveZSize;

    // Add in time to model them over time
    waves += _WaveAndDistance.x * waveSpeed;

    float4 s, c;
    waves = frac (waves);
    FastSinCos (waves, s,c);

    s = s * s;

    s = s * s;

    half lighting = dot (s, normalize (half4 (1,1,.4,.2))) * 0.7;

    s = s * waveAmount;

    half3 waveMove = 0;
    waveMove.x = dot (s, _waveXmove);
    waveMove.z = dot (s, _waveZmove);

    vertex.xz -= waveMove.xz * _WaveAndDistance.z;

    // apply color animation
    half3 waveColor = lerp (0.5, _WavingTint.rgb, lighting);

    // Fade the grass out before detail distance.
    // Saturate because Radeon HD drivers on OS X 10.4.10 don't saturate vertex colors properly.
    half3 offset = vertex.xyz - _CameraPosition.xyz;
    color.a = saturate (2 * (_WaveAndDistance.w - dot (offset, offset)) * _CameraPosition.w);

    return half4(2 * waveColor * color.rgb, color.a);
}

void TerrainBillboardGrass( inout float4 pos, float2 offset )
{
    float3 grasspos = pos.xyz - _CameraPosition.xyz;
    if (dot(grasspos, grasspos) > _WaveAndDistance.w)
        offset = 0.0;
    pos.xyz += offset.x * _CameraRight.xyz;
    pos.y += offset.y;
}

#endif // LIGHTWEIGHT_INPUT_SURFACE_GRASS_INCLUDED