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// Globals
TEXTURE2D(WIND_SETTINGS_TexNoise);
SAMPLER(sampler_WIND_SETTINGS_TexNoise);
TEXTURE2D(WIND_SETTINGS_TexGust);
SAMPLER(sampler_WIND_SETTINGS_TexGust);
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 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;
};
float3 texNoise(float3 worldPos, float LOD)
{
return SAMPLE_TEXTURE2D_LOD(WIND_SETTINGS_TexNoise, sampler_WIND_SETTINGS_TexNoise, worldPos.xz, LOD).xyz -0.5;
}
float texGust(float3 worldPos, float LOD)
{
return SAMPLE_TEXTURE2D_LOD(WIND_SETTINGS_TexGust, sampler_WIND_SETTINGS_TexGust, worldPos.xz, 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 > 0.0f || WIND_SETTINGS_Turbulence > 0.0f)
{
trunk = texNoise((PivotPosition - worldOffset)*WIND_SETTINGS_FlexNoiseScale,3);
}
float gust = 0.0f;
if(WIND_SETTINGS_GustSpeed > 0.0f)
{
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;
return result;
}
void ApplyWindDisplacement( inout float3 positionWS,
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 > 0.0f)
{
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;
}
}