BEGIN_OPTIONS
   ShaderName "AwesomeTechnologies/Development/Trees/VertexWind"     
   Stackable "True"                
END_OPTIONS

BEGIN_PROPERTIES
	_InitialBend("Wind Initial Bend", Float) = 1
	_Stiffness("Wind Stiffness", Float) = 1
	_Drag("Wind Drag", Float) = 1
	_ShiverDrag("Wind Shiver Drag", Float) = 0.05
	_WindNormalInfluence("Wind Normal Influence", Float) = 0	
END_PROPERTIES

BEGIN_DEFINES
#define FLT_EPSILON 1.192092896e-07 
END_DEFINES

BEGIN_CODE

sampler2D WIND_SETTINGS_TexNoise;
sampler2D WIND_SETTINGS_TexGust;

float _InitialBend;
float _Stiffness;
float _Drag;
float _ShiverDrag;
float _ShiverDirectionality;
float _WindNormalInfluence;
float4 _NewNormal;

float4  WIND_SETTINGS_WorldDirectionAndSpeed;
float   WIND_SETTINGS_FlexNoiseScale;
float   WIND_SETTINGS_ShiverNoiseScale;
float   WIND_SETTINGS_Turbulence;
float   WIND_SETTINGS_GustSpeed;
float   WIND_SETTINGS_GustScale;
float   WIND_SETTINGS_GustWorldScale;

float PositivePow_(float base, float power)
{
    return pow(max(abs(base), float(FLT_EPSILON)), power);
}

float AttenuateTrunk_(float x, float s)
{
    float r = (x / s);
    return PositivePow_(r,1/s);
}

float3 Rotate_(float3 pivot, float3 position, float3 rotationAxis, float angle)
{
    rotationAxis = normalize(rotationAxis);
    float3 cpa = pivot + rotationAxis * dot(rotationAxis, position - pivot);
    return cpa + ((position - cpa) * cos(angle) + cross(rotationAxis, (position - cpa)) * sin(angle));
}

struct WindData_
{
    float3 Direction;
    float Strength;
    float3 ShiverStrength;
    float3 ShiverDirection;
	float Gust;
};

float3 texNoise_(float3 worldPos, float LOD)
{
	return tex2Dlod(WIND_SETTINGS_TexNoise,float4(worldPos.xz,0,LOD)).xyz -0.5;
}

float texGust_(float3 worldPos, float LOD)
{
    return tex2Dlod(WIND_SETTINGS_TexGust, float4(worldPos.xz,0, LOD)).x;
}

WindData_ GetAnalyticalWind(float3 WorldPosition, float3 PivotPosition, float drag, float shiverDrag, float initialBend, float4 time)
{
    WindData_ result;
    float3 normalizedDir = normalize(WIND_SETTINGS_WorldDirectionAndSpeed.xyz);

    float3 worldOffset = normalizedDir * WIND_SETTINGS_WorldDirectionAndSpeed.w * time.y;
    float3 gustWorldOffset = normalizedDir * WIND_SETTINGS_GustSpeed * time.y;

    // Trunk noise is base wind + gusts + noise

    float3 trunk = float3(0,0,0);

    if(WIND_SETTINGS_WorldDirectionAndSpeed.w > 0.0 || WIND_SETTINGS_Turbulence > 0.0)
    {
        trunk = texNoise_((PivotPosition - worldOffset)*WIND_SETTINGS_FlexNoiseScale,3);
    }

    float gust  = 0.0;

    if(WIND_SETTINGS_GustSpeed > 0.0)
    {
        gust = texGust_((PivotPosition - gustWorldOffset)*WIND_SETTINGS_GustWorldScale,3);
        gust = pow(gust, 2) * WIND_SETTINGS_GustScale;
    }

    float3 trunkNoise =
        (
                (normalizedDir * WIND_SETTINGS_WorldDirectionAndSpeed.w)
                + (gust * normalizedDir * WIND_SETTINGS_GustSpeed)
                + (trunk * WIND_SETTINGS_Turbulence)
        ) * drag;

    // Shiver Noise
    float3 shiverNoise = texNoise_((WorldPosition - worldOffset)*WIND_SETTINGS_ShiverNoiseScale,0) * shiverDrag * WIND_SETTINGS_Turbulence;

    float3 dir = trunkNoise;
    float flex = length(trunkNoise) + initialBend;
    float shiver = length(shiverNoise);

    result.Direction = dir;
    result.ShiverDirection = shiverNoise;
    result.Strength = flex;
    result.ShiverStrength = shiver + shiver * gust;
	result.Gust = (gust * normalizedDir * WIND_SETTINGS_GustSpeed)
		+ (trunk * WIND_SETTINGS_Turbulence);

    return result;
}

void ApplyWindDisplacement_( inout float3    positionWS,
							inout WindData_    windData,
                            float3          normalWS,
                            float3          rootWP,
                            float           stiffness,
                            float           drag,
                            float           shiverDrag,
                            float           shiverDirectionality,
                            float           initialBend,
                            float           shiverMask,
                            float4          time)
{
    WindData_ wind = GetAnalyticalWind(positionWS, rootWP, drag, shiverDrag, initialBend, time);

    if (wind.Strength > 0.0)
    {
        float att = AttenuateTrunk_(distance(positionWS, rootWP), stiffness);
        float3 rotAxis = cross(float3(0, 1, 0), wind.Direction);

        positionWS = Rotate_(rootWP, positionWS, rotAxis, (wind.Strength) * 0.001 * att);

        float3 shiverDirection = normalize(lerp(normalWS, normalize(wind.Direction + wind.ShiverDirection), shiverDirectionality));
        positionWS += wind.ShiverStrength * shiverDirection * shiverMask;
    }
	windData = wind;

}

float3 TransformObjectToWorldNormal_(float3 normalOS)
{
#ifdef UNITY_ASSUME_UNIFORM_SCALING
    return UnityObjectToWorldDir(normalOS);
#else
    return normalize(mul(normalOS, (float3x3)GetWorldToObjectMatrix()));
#endif
}   
	 void ModifyVertex(inout VertexData v, inout ExtraV2F d)
	 {
     		float3 positionWS = TransformObjectToWorld(v.vertex.xyz);
     		float3 rootWP = TransformObjectToWorld(float3(0,0,0));
     		if (positionWS.y > rootWP.y)
     		{
     			float3 normalWS = TransformObjectToWorldNormal_(v.normal);
     			WindData_ windData;
     			ApplyWindDisplacement_(positionWS, windData, normalWS, rootWP, _Stiffness, _Drag, _ShiverDrag, _ShiverDirectionality, _InitialBend, v.vertexColor.a, _Time);
     			v.vertex.xyz = TransformWorldToObject(positionWS).xyz;
     		}
	 }

	void SurfaceFunction(inout Surface o, ShaderData d)
	{
	
	}

END_CODE