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CWindStateMgr class

The CWindStateMgr class is declared and defined in Include/SpeedTree/Core/SpeedTreeWind.h. As highlighted in yellow in the figure below, CWindStateMgr feeds state information into a wind-enabled vertex shader through shader constants. The state is defined by an artist in the Modeler application when the wind behavior is tuned.

diagram_wind_system_cwindstatemgr.jpeg

CWindStateMgr is the same class used by all versions of the Modeler (games, cinematic, and subscription) and can support all of SpeedTree's different wind modes, though the Games SDK uses the “SDK” wind mode only. The state passed by CWindStateMgr is encapsulated in SWindInputSdk::m_sState, where m_sState is of type SWindStateSdk also defined in Include/SpeedTree/Core/SpeedTreeWind.h but also listed below: 

struct SWindBranchStateSdk
{
    float3              m_vNoisePosTurbulence;
    float               m_fIndependence;
 
    float               m_fBend;
    float               m_fOscillation;
    float               m_fTurbulence;
    float               m_fFlexibility;
};
 
struct SWindRippleStateSdk
{
    float3               m_vNoisePosTurbulence;
    float                m_fIndependence;
 
    float                m_fPlanar;
    float                m_fDirectional;
    float                m_fFlexibility;
    float                m_fShimmer;
};
 
struct SWindStateSdk
{
    float3               m_vWindDirection;
    float                m_fWindStrength;
 
    float3               m_vBoundingBoxMin;
    float                m_fSharedHeightStart;
    float3               m_vBoundingBoxMax;
    float                m_fBranch1StretchLimit;
 
    SWindBranchStateSdk  m_sShared;
    SWindBranchStateSdk  m_sBranch1;
    SWindBranchStateSdk  m_sBranch2;
    SWindRippleStateSdk  m_sRipple;
 
    float                m_fBranch2StretchLimit;
};

Initialization

Each instantiation of a CCore object (which represents a base tree model) has its own CWindStateMgr object. CWindStateMgr has a series of overloading Configure() functions, one of which takes a SConfigSdk. SConfigSdk contains all of the wind behavior parameters set by the artist in the Modeler. When an .stsdk file is loaded via CCore::LoadTree(), the CWindStateMgr object embedded in that CCore object is automatically initialized with the SConfigSdk-related data embedded in the .stsdk file.

The relationship between SConfigSdk and SWindStateSdk is that SConfigSdk contains a complete definition of the wind profile set in the Modeler whereas SWindStateSdk houses the data the wind shader functions need at a particular snapshot in time.

Forest library wind functions

The CForest class provides convenience functions for controlling the wind for a set of base trees without having to access each tree separately. The functions include the following:

Function Description
CForest::WindEnable() This is an initialization-level function and shouldn't be called to enable/disable the wind while the rendering loop is active. If wind is to be supported, call this function once during initialization.
CForest::WindAdvance() Advances the wind simulation for all of the base tree objects in the forest. The second parameter, time, is in seconds and represents time since the beginning of the simulation, not the time since the last call or frame. Not free in terms of CPU but not expensive.
CForest::WindPreroll() A convenience function for bypassing the start-up state of the wind simulation. It's common to use a 10-second or so pre-roll.
CForest::WindSetStrength() Updates the strength of all of the base trees in the forest.
CForest::WindSetDirection() Updates the direction of all of the base trees in the forest.

You can still set an individual base tree's wind parameters by querying the CWind object of a CTree and setting its parameters directly. All of the instances of a CTree share this wind object. Each will have its own slight variation of the wind, as provided by the wind shader's usage of the tree's position as a unique numerical identifier. However, all of the wind parameters set for the base tree in the Modeler application will remain the same across all its instances.