SOP_BouncyAgent.C

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/*! @file SOP_BouncyAgent.C

  @brief Demonstrates example for creating a procedural agent primitive.

  The node creates an agent primitive for every point from its input geometry
  that uses the same shared agent definition. The agent definition itself is a
  unit polygonal sphere that has skin weights bound to two joints (a parent and
  a child) with animation that bounces it in TY.

*/

#include "SOP_BouncyAgent.h"

#include <OP/OP_AutoLockInputs.h>
#include <OP/OP_Operator.h>
#include <OP/OP_OperatorTable.h>
#include <PRM/PRM_Include.h>
#include <PRM/PRM_Type.h>
#include <CH/CH_Manager.h>
#include <GU/GU_Agent.h>
#include <GU/GU_AgentBlendShapeUtils.h>
#include <GU/GU_AgentRig.h>
#include <GU/GU_AgentShapeLib.h>
#include <GU/GU_AgentLayer.h>
#include <GU/GU_PrimPacked.h>
#include <GU/GU_PrimSphere.h>
#include <GEO/GEO_AttributeCaptureRegion.h>
#include <GEO/GEO_AttributeIndexPairs.h>
#include <GA/GA_AIFIndexPair.h>
#include <GA/GA_Names.h>
#include <CL/CL_Clip.h>
#include <CL/CL_Track.h>
#include <UT/UT_Array.h>
#include <UT/UT_DSOVersion.h>
#include <UT/UT_JSONParser.h>
#include <UT/UT_JSONWriter.h>
#include <UT/UT_Interrupt.h>
#include <UT/UT_String.h>
#include <UT/UT_StringArray.h>
#include <UT/UT_WorkBuffer.h>
#include <stdlib.h>

using namespace HDK_Sample;

// Provide entry point for installing this SOP.
void
newSopOperator(OP_OperatorTable *table)
{
    OP_Operator *op = new OP_Operator(
        "hdk_bouncyagent",
        "BouncyAgent",
        SOP_BouncyAgent::myConstructor,
        SOP_BouncyAgent::myTemplateList,
        1,      // min inputs
        1       // max inputs
        );
    table->addOperator(op);
}

OP_Node *
SOP_BouncyAgent::myConstructor(
        OP_Network *net, const char *name, OP_Operator *op)
{
    return new SOP_BouncyAgent(net, name, op);
}

// SOP Parameters.
static PRM_Name     sopAgentName("agentname", "Agent Name");
static PRM_Default  sopAgentNameDef(0, "agent1");
static PRM_Name     sopHeight("height", "Height");
static PRM_Default  sopHeightDef(5.0);
static PRM_Name     sopClipLength("cliplength", "Clip Length"); // seconds
static PRM_Name     sopClipOffset("clipoffset", "Clip Offset"); // seconds
static PRM_Default  sopClipOffsetDef(0, "$T");
static PRM_Range    sopClipOffsetRange(PRM_RANGE_UI, 0, PRM_RANGE_UI, 10);
static PRM_Name     sopEnableBlendshapes("enableblendshapes",
                                         "Enable Blendshapes");
static PRM_Name     sopReload("reload", "Reload");

PRM_Template
SOP_BouncyAgent::myTemplateList[] =
{
    PRM_Template(PRM_ALPHASTRING,   1, &sopAgentName, &sopAgentNameDef),
    PRM_Template(PRM_FLT_J,         1, &sopHeight, &sopHeightDef),
    PRM_Template(PRM_FLT_J,         1, &sopClipLength, PRMoneDefaults,
                                    0, &PRMrulerRange),
    PRM_Template(PRM_FLT_J,         1, &sopClipOffset, &sopClipOffsetDef,
                                    0, &sopClipOffsetRange),
    PRM_Template(PRM_TOGGLE_J,      1, &sopEnableBlendshapes, PRMzeroDefaults),
    PRM_Template(PRM_CALLBACK,      1, &sopReload, 0, 0, 0,
                                    &SOP_BouncyAgent::onReload),
    PRM_Template() // sentinel
};

// Constructor
SOP_BouncyAgent::SOP_BouncyAgent(
        OP_Network *net, const char *name, OP_Operator *op)
    : SOP_Node(net, name, op)
{
    // This indicates that this SOP manually manages its data IDs,
    // so that Houdini can identify what attributes may have changed,
    // e.g. to reduce work for the viewport, or other SOPs that
    // check whether data IDs have changed.
    // By default, (i.e. if this line weren't here), all data IDs
    // would be bumped after the SOP cook, to indicate that
    // everything might have changed.
    // If some data IDs don't get bumped properly, the viewport
    // may not update, or SOPs that check data IDs
    // may not cook correctly, so be *very* careful!
    mySopFlags.setManagesDataIDs(true);
}

// Destructor
SOP_BouncyAgent::~SOP_BouncyAgent()
{
}

enum
{
    SOP_SKIN_RIG_INDEX = 0,
    SOP_PARENT_RIG_INDEX,
    SOP_CHILD_RIG_INDEX,
    // Set up exclusive rig index range for joints
    SOP_JOINT_BEGIN = SOP_PARENT_RIG_INDEX,
    SOP_JOINT_END   = SOP_CHILD_RIG_INDEX + 1
};

static constexpr UT_StringLit theChannel1Name("channel1");
static constexpr UT_StringLit theChannel2Name("channel2");

// Create the rig.
// Rigs define the names of the transforms in a tree hierarchy.
static GU_AgentRigPtr
sopCreateRig(const char *path, bool enable_blendshapes)
{
    UT_String rig_name = path;
    rig_name += "?rig";
    GU_AgentRigPtr rig = GU_AgentRig::addRig(rig_name);

    UT_StringArray transforms;
    transforms.append("skin");      // SOP_SKIN_RIG_INDEX
    transforms.append("parent");    // SOP_PARENT_RIG_INDEX
    transforms.append("child");     // SOP_CHILD_RIG_INDEX

    UT_IntArray child_counts;
    child_counts.append(0); // 'skin' has 0 children
    child_counts.append(1); // 'parent' has 1 child
    child_counts.append(0); // 'child' has 0 children

    UT_IntArray children;
    // 'skin' has no children so we don't need to append anything for it
    children.append(SOP_CHILD_RIG_INDEX); // 'parent' has 'child' as the child
    // 'child' has no children so we don't need to append anything for it

    // now construct the rig
    if (!rig->construct(transforms, child_counts, children))
        return nullptr;

    // Define a couple channels for use with the blendshape deformer.
    if (enable_blendshapes)
    {
        UT_StringArray channels;
        channels.append(theChannel1Name.asHolder());
        channels.append(theChannel2Name.asHolder());

        UT_Array<GU_AgentRig::FloatType> default_values;
        default_values.appendMultiple(0.0, 2);

        // These channels are not associated with any joint.
        UT_IntArray transforms;
        transforms.appendMultiple(-1, 2);

        UT_StringArray errors;
        if (!rig->addChannels(channels, default_values, transforms, errors))
            return nullptr;
    }

    return rig;
}

static GU_Detail *
sopCreateSphere(bool for_default)
{
    GU_Detail *shape = new GU_Detail;
    GU_PrimSphereParms sphere(shape);
    if (for_default)
    {
        sphere.freq = 2;
        sphere.type = GEO_PATCH_TRIANGLE;
        GU_PrimSphere::build(sphere, GEO_PRIMPOLY);
    }
    else
    {
        // Position and scale the collision sphere to account for the
        // deformation animation.
        sphere.xform.scale(1.5, 1, 1.5);
        sphere.xform.translate(0, 1, 0.5);
        GU_PrimSphere::build(sphere, GEO_PRIMSPHERE);
    }
    return shape;
}

/// Create a blendshape input from a sparse subset of the base shape's points.
static void
sopAddBlendshapeInput(const GU_Detail &src, int increment,
                      const UT_StringRef &channel_name, GU_DetailHandle &gdh,
                      UT_StringHolder &shape_name)
{
    shape_name.format("{}.blendshape.{}", GU_AGENT_LAYER_DEFAULT,
                       channel_name);

    GU_Detail *gdp = new GU_Detail;
    gdh.allocateAndSet(gdp);

    // The 'id' attribute is used to match up points from the base shape.
    GA_RWHandleI id_attrib =
        gdp->addIntTuple(GA_ATTRIB_POINT, GA_Names::id, 1, GA_Defaults(-1));

    UT_Matrix4D xform(1.0);
    xform.scale(1.5);

    const GA_Size n = src.getNumPoints() / increment;
    GA_Offset ptoff = gdp->appendPointBlock(n);
    for (GA_Index i = 0; i < n; ++i, ++ptoff)
    {
        const GA_Index src_idx = i * increment;
        UT_Vector3 pos = src.getPos3(src.pointOffset(src_idx)) * xform;

        gdp->setPos3(ptoff, pos);
        id_attrib.set(ptoff, src_idx);
    }
}

static void
sopAddBlendshapes(const GU_AgentRig &rig, GU_AgentShapeLib &shapelib,
                  GU_DetailHandle &base_shape)
{
    GU_DetailHandleAutoWriteLock base_shape_gdp(base_shape);

    // Create the input shapes and add them to the shape library.
    GU_DetailHandle shape1;
    UT_StringHolder shape1_name;
    sopAddBlendshapeInput(*base_shape_gdp, 3, theChannel1Name.asRef(), shape1,
                          shape1_name);
    GU_DetailHandle shape2;
    UT_StringHolder shape2_name;
    sopAddBlendshapeInput(*base_shape_gdp, 4, theChannel2Name.asRef(), shape2,
                          shape2_name);

    shapelib.addShape(shape1_name, shape1);
    shapelib.addShape(shape2_name, shape2);

    // Add these shapes as inputs for the base shape, so that the blendshape
    // deformer can locate them.
    UT_StringArray shape_names;
    shape_names.append(shape1_name);
    shape_names.append(shape2_name);

    UT_StringArray channel_names;
    channel_names.append(theChannel1Name.asHolder());
    channel_names.append(theChannel2Name.asHolder());

    GU_AgentBlendShapeUtils::addInputsToBaseShape(*base_shape_gdp, shape_names,
                                                  channel_names);
}

// For simplicity, we bind all points to all the transforms except for
// SOP_SKIN_RIG_INDEX.
static void
sopAddSkinWeights(const GU_AgentRig &rig, const GU_DetailHandle &shape)
{
    GU_DetailHandleAutoWriteLock gdl(shape);
    GU_Detail *gdp = gdl.getGdp();

    // Create skinning attribute with 2 regions and each point is bound to both
    // rig transforms.
    int num_regions = (SOP_JOINT_END - SOP_JOINT_BEGIN);
    GEO_Detail::geo_NPairs num_pairs_per_pt(num_regions);
    GA_RWAttributeRef capt = gdp->addPointCaptureAttribute(num_pairs_per_pt);
    int regions_i = -1;
    GA_AIFIndexPairObjects *regions
        = GEO_AttributeCaptureRegion::getBoneCaptureRegionObjects(
                                                            capt, regions_i);
    regions->setObjectCount(num_regions);

    // Tell the skinning attribute the names of the rig transforms. This needs
    // to be done after calling regions->setObjectCount().
    GEO_RWAttributeCapturePath paths(gdp);
    for (int i = 0; i < num_regions; ++i)
        paths.setPath(i, rig.transformName(SOP_JOINT_BEGIN + i));

    // Set up the rest transforms for the skin weight bindings. For efficiency,
    // these are actually stored in the skin weight bindings as the INVERSE of
    // the world space rest transform of the joint.
    for (int i = 0; i < num_regions; ++i)
    {
        GEO_CaptureBoneStorage r;
        // Recall that the unit sphere is created at the origin. So to position
        // the parent joint at the base of the sphere, it should be a position
        // (0, -1, 0). However, since these are actually inverses, we'll
        // translate by the opposite sign instead.
        if (i == 0)
            r.myXform.translate(0, +1.0, 0);
        else
            r.myXform.translate(0, -1.0, 0);
        regions->setObjectValues(i, regions_i, r.floatPtr(),
                                 GEO_CaptureBoneStorage::tuple_size);
    }

    // Set up the weights
    const GA_AIFIndexPair *weights = capt->getAIFIndexPair();
    weights->setEntries(capt, num_regions);
    for (GA_Offset ptoff : gdp->getPointRange())
    {
        for (int i = 0; i < num_regions; ++i)
        {
            // Set the region index that the point is captured by.
            // Note that these index into 'paths' above.
            weights->setIndex(capt, ptoff, /*entry*/i, /*region*/i);
            // Set the weight that the point is captured by transform i.
            // Notice that all weights for the point should sum to 1.
            fpreal weight = 1.0/num_regions;
            weights->setData(capt, ptoff, /*entry*/i, weight);
        }
    }
}

// Default convention is to prefix the shape name by the layer name
#define SOP_DEFAULT_SKIN_NAME   GU_AGENT_LAYER_DEFAULT".skin"
#define SOP_COLLISION_SKIN_NAME GU_AGENT_LAYER_COLLISION".skin"

// Create the shape library which contains a list of all the shape geometries
// that can be attached to the rig transforms.
static GU_AgentShapeLibPtr
sopCreateShapeLib(const char *path, const GU_AgentRig &rig,
                  bool enable_blendshapes)
{
    UT_String shapelib_name = path;
    shapelib_name += "?shapelib";
    GU_AgentShapeLibPtr shapelib = GU_AgentShapeLib::addLibrary(shapelib_name);

    GU_DetailHandle skin_geo;
    skin_geo.allocateAndSet(sopCreateSphere(true), /*own*/true);
    sopAddSkinWeights(rig, skin_geo);

    if (enable_blendshapes)
        sopAddBlendshapes(rig, *shapelib, skin_geo);

    shapelib->addShape(SOP_DEFAULT_SKIN_NAME, skin_geo);

    // The collision geometry is intended to be simplified versions of the
    // default layer shapes. The bounding box for the default layer shape is
    // computed from the corresponding collision layer shape.
    GU_DetailHandle coll_geo;
    coll_geo.allocateAndSet(sopCreateSphere(false), /*own*/true);
    shapelib->addShape(SOP_COLLISION_SKIN_NAME, coll_geo);

    return shapelib;
}

// Create a default layer with the sphere as the geometry bound to the rig.
// Layers assign geometry from the shapelib to be used for the rig
// transforms.
// Agents must have at least 2 layers:
//          GU_AGENT_LAYER_DEFAULT ("default"
//              - Used for display/render
//          GU_AGENT_LAYER_COLLISION ("collision")
//              - Simple geometry to be used for the bounding box that
//                encompasses the corresponding shape in default layer for all
//                possible local deformations.
// In general, it can have more layers and we can set which of those we use
// for the default and collision.
static GU_AgentLayerPtr
sopCreateDefaultLayer(
        const char *path,
        const GU_AgentRigPtr &rig,
        const GU_AgentShapeLibPtr &shapelib,
        bool enable_blendshapes)
{
    UT_StringArray shape_names;
    UT_Array<exint> transform_indices;
    UT_Array<GU_AgentShapeDeformerConstPtr> deformers;
    UT_Array<UT_Vector3F> bounds_scales;

    // Simply bind the skin geometry to the 'skin' transform which we know is
    // transform index 0.
    shape_names.append(SOP_DEFAULT_SKIN_NAME);
    transform_indices.append(SOP_SKIN_RIG_INDEX);

    // Use either the normal linear skin deformer, or the blendshape + skin
    // deformer.
    // For a shape that is rigidly transformed, no deformer is needed (nullptr)
    if (enable_blendshapes)
        deformers.append(GU_AgentLayer::getBlendShapeAndSkinDeformer());
    else
        deformers.append(GU_AgentLayer::getLinearSkinDeformer());

    bounds_scales.append(UT_Vector3F(1.0));

    UT_String unique_name = path;
    unique_name += "?default_layer";
    GU_AgentLayerPtr layer
        = GU_AgentLayer::addLayer(unique_name, rig, shapelib);
    if (!layer->construct(
                shape_names, transform_indices, deformers, bounds_scales))
    {
        return nullptr;
    }

    UT_StringHolder layer_name(UTmakeUnsafeRef(GU_AGENT_LAYER_DEFAULT));
    layer->setName(layer_name);

    return layer;
}

// See also comments for sopCreateDefaultLayer().
static GU_AgentLayerPtr
sopCreateCollisionLayer(
        const char *path,
        const GU_AgentRigPtr &rig,
        const GU_AgentShapeLibPtr &shapelib)
{
    UT_StringArray shape_names;
    UT_Array<exint> transform_indices;
    UT_Array<GU_AgentShapeDeformerConstPtr> deformers;
    UT_Array<UT_Vector3F> bounds_scales;

    // For character rigs, the collision shapes are typically attached to the
    // joint transforms so that they can proxy for skin deformation.
    shape_names.append(SOP_COLLISION_SKIN_NAME);
    transform_indices.append(SOP_PARENT_RIG_INDEX);
    deformers.append(nullptr); // has no deformer
    bounds_scales.append(UT_Vector3F(1.0));

    UT_String unique_name = path;
    unique_name += "?collision_layer";
    GU_AgentLayerPtr
        layer = GU_AgentLayer::addLayer(unique_name, rig, shapelib);
    if (!layer->construct(
                shape_names, transform_indices, deformers, bounds_scales))
    {
        return nullptr;
    }

    UT_StringHolder layer_name(UTmakeUnsafeRef(GU_AGENT_LAYER_COLLISION));
    layer->setName(layer_name);

    return layer;
}

static fpreal*
sopAddTrack(CL_Clip &chans, const GU_AgentRig &rig, int i, const char *trs_name)
{
    UT_WorkBuffer str;
    str.sprintf("%s:%s", rig.transformName(i).buffer(), trs_name);
    return chans.addTrack(str.buffer())->getData();
}

// Create some bouncy animation for the agent
static GU_AgentClipPtr
sopCreateBounceClip(CL_Clip &chans, const GU_AgentRigPtr &rig, fpreal height,
                    bool enable_blendshapes)
{
    int num_samples = chans.getTrackLength();

    // Set the ty of the 'parent' transform that bounces. Note that these
    // transforms here are in local space. The valid channel names are:
    //      Translate:  tx ty tz
    //      Rotate:     rx ry rz (euler angles in degrees, XYZ rotation order)
    //      Scale:      sx sy sz
    fpreal *ty = sopAddTrack(chans, *rig, SOP_PARENT_RIG_INDEX, "ty");
    fpreal *sy = sopAddTrack(chans, *rig, SOP_PARENT_RIG_INDEX, "sy");
    for (int i = 0; i < num_samples; ++i)
    {
        ty[i] = height * SYSsin(i * M_PI / (num_samples-1));
        // add some squash and stretch
        sy[i] = 1.0 - SYSabs(0.5 * SYSsin(i * M_PI / (num_samples-1)));
    }

    // Set the ty of the 'child' transform. Note that these transforms here are
    // in local space.
    fpreal *tz = sopAddTrack(chans, *rig, SOP_CHILD_RIG_INDEX, "tz");
    ty = sopAddTrack(chans, *rig, SOP_CHILD_RIG_INDEX, "ty");
    for (int i = 0; i < num_samples; ++i)
    {
        ty[i] = 2.0;                                    // sphere diameter
        tz[i] = 1.5 * SYSsin(i * M_PI / (num_samples-1));       // sway a bit forwards
    }

    // Set up channels to drive the blendshapes.
    if (enable_blendshapes)
    {
        fpreal *chan1 = chans.addTrack(theChannel1Name.asHolder())->getData();
        fpreal *chan2 = chans.addTrack(theChannel2Name.asHolder())->getData();

        for (int i = 0; i < num_samples; ++i)
        {
            chan1[i] = 0.5 + 0.5 * SYScos(i * 2 * M_PI / num_samples + M_PI);
            chan2[i] = 0.5 + 0.5 * SYScos(i * 2 * M_PI / num_samples);
        }
    }

    // Finally load the agent clip from the CL_Clip animation we created
    GU_AgentClipPtr clip = GU_AgentClip::addClip("bounce", rig);
    if (!clip)
        return nullptr;
    clip->load(chans);

    return clip;
}

static constexpr UT_StringLit theCustomDataItemType("bouncyagentdata");
static constexpr UT_StringLit theValueToken("myvalue");
static constexpr UT_StringLit theNameToken("myname");

/// Example implementation of a custom data item that can be added to a
/// GU_AgentDefinition.
class GU_BouncyAgentCustomData : public GU_AgentCustomDataItem
{
public:
    GU_BouncyAgentCustomData() : myValue(0) {}

    GU_BouncyAgentCustomData(const UT_StringHolder &name, int value)
        : GU_AgentCustomDataItem(), myName(name), myValue(value)
    {
    }

    static GU_AgentCustomDataItemPtr construct(const GU_AgentDefinition &)
    {
        return new GU_BouncyAgentCustomData();
    }

    const UT_StringHolder &dataItemType() const override
    {
        return theCustomDataItemType.asHolder();
    }

    int64 getMemoryUsage(bool inclusive) const override
    {
        int64 mem = inclusive ? sizeof(*this) : 0;
        mem += myName.getMemoryUsage(false);
        return mem;
    }

    const UT_StringHolder &name() const override { return myName; }
    int value() const { return myValue; }

    /// @{
    /// Implements serialization to and from JSON.
    /// For debugging, save to an ASCII (.geo) geometry file.
    bool load(UT_JSONParser &p) override
    {
        UT_StringHolder key;
        for (auto it = p.beginMap(); !it.atEnd(); ++it)
        {
            if (!p.parseKey(key))
                return false;

            if (key == theValueToken.asHolder())
            {
                if (!p.parseInt(myValue))
                    return false;
            }
            else if (key == theNameToken.asHolder())
            {
                if (!p.parseString(myName))
                    return false;
            }
            else
            {
                p.addWarning("Unknown key '%s'", key.buffer());
                if (!p.skipNextObject())
                    return false;
            }
        }

        return true;
    }

    bool save(UT_JSONWriter &w) const override
    {
        bool ok = true;
        ok = ok && w.jsonBeginMap();

        ok = ok && w.jsonKey(theNameToken.asHolder());
        ok = ok && w.jsonValue(myName);

        ok = ok && w.jsonKey(theValueToken.asHolder());
        ok = ok && w.jsonValue(myValue);

        ok = ok && w.jsonEndMap();
        return ok;
    }
    /// @}

private:
    UT_StringHolder myName;
    int64 myValue;
};

/// Entry point for registering GU_BouncyAgentCustomData.
void
GUregisterAgentCustomDataItemType()
{
    GU_AgentDefinition::registerCustomDataItemType(
        theCustomDataItemType.asHolder(), GU_BouncyAgentCustomData::construct);
}

// Enable this to debug our definition
#define SOP_SAVE_AGENT_DEFINITION 0

// Create the agent definition
GU_AgentDefinitionPtr
SOP_BouncyAgent::createDefinition(fpreal t) const
{
    // Typically, the definition is loaded from disk which has a filename for
    // each of the different parts. Since we're doing this procedurally, we're
    // going to just make up some arbitrary unique names using our node path.
    UT_String path;
    getFullPath(path);

    const bool enable_blendshapes = BLENDSHAPES(t);

    GU_AgentRigPtr rig = sopCreateRig(path, enable_blendshapes);
    if (!rig)
        return nullptr;

    GU_AgentShapeLibPtr shapelib =
        sopCreateShapeLib(path, *rig, enable_blendshapes);
    if (!shapelib)
        return nullptr;

    GU_AgentLayerPtr default_layer =
        sopCreateDefaultLayer(path, rig, shapelib, enable_blendshapes);
    if (!default_layer)
        return nullptr;

    GU_AgentLayerPtr collision_layer = sopCreateCollisionLayer(path,
                                                               rig, shapelib);
    if (!collision_layer)
        return nullptr;

    CL_Clip chans(CHgetManager()->getSample(CLIPLENGTH(t)));
    chans.setSampleRate(CHgetManager()->getSamplesPerSec());
    GU_AgentClipPtr clip =
        sopCreateBounceClip(chans, rig, HEIGHT(t), enable_blendshapes);
    if (!clip)
        return nullptr;

#if SOP_SAVE_AGENT_DEFINITION
    // Once we have the definition, we can save out the files for loading with
    // the Agent SOP as well. Or, we can examine them for debugging purposes.
    {
        UT_AutoJSONWriter writer("bouncy_rig.rig", /*binary*/false);
        rig->save(writer);
    }
    {
        UT_AutoJSONWriter writer("bouncy_shapelib.bgeo", /*binary*/true);
        shapelib->save(writer);
    }
    {
        UT_AutoJSONWriter writer("bouncy_layer.default.lay", /*binary*/false);
        default_layer->save(writer);
    }
    {
        UT_AutoJSONWriter writer("bouncy_layer.collision.lay", /*binary*/false);
        collision_layer->save(writer);
    }
    {
        chans.save("bouncy_bounce.bclip");
    }
#endif

    // The agent definition is used to create agent primitives. Many agent
    // primitives can share the same definition.
    GU_AgentDefinitionPtr def(new GU_AgentDefinition(rig, shapelib));
    // The definition has a number of layers that be can assigned
    def->addLayer(default_layer);
    def->addLayer(collision_layer);
    // ... and a number of clips that can be assigned to specific agent prims
    def->addClip(clip);

    // Add some custom data for demonstration purposes.
    def->addCustomDataItem(new GU_BouncyAgentCustomData("mycustomdata", 42));

    return def;
}

/*static*/ int
SOP_BouncyAgent::onReload(
        void *data, int index, fpreal t, const PRM_Template *tplate)
{
    SOP_BouncyAgent* sop = static_cast<SOP_BouncyAgent*>(data);
    if (!sop->getHardLock()) // only allow reloading if we're not locked
    {
        sop->myDefinition.reset();
        sop->forceRecook();
    }
    return 1;
}

// Compute the output geometry for the SOP.
OP_ERROR
SOP_BouncyAgent::cookMySop(OP_Context &context)
{
    fpreal t = context.getTime();

    // We must lock our inputs before we try to access their geometry.
    // OP_AutoLockInputs will automatically unlock our inputs when we return.
    // NOTE: Don't call unlockInputs yourself when using this!
    OP_AutoLockInputs inputs(this);
    if (inputs.lock(context) >= UT_ERROR_ABORT)
        return error();

    // Duplicate the input geometry, but only if it was changed
    int input_changed;
    duplicateChangedSource(/*input*/0, context, &input_changed);

    // Detect if we need to rebuild the agent definition. For simplicity, we'll
    // rebuild if any of our agent parameters changed. Note the use of the
    // bitwise or operator to ensure that isParmDirty() is always called for
    // all parameters.
    bool agent_changed = isParmDirty(sopAgentName.getToken(), t);
    agent_changed = isParmDirty(sopHeight.getToken(), t);
    agent_changed |= isParmDirty(sopClipLength.getToken(), t);
    agent_changed |= isParmDirty(sopEnableBlendshapes.getToken(), t);

    if (!myDefinition)
    {
        agent_changed = true;
        input_changed = true;
    }

    if (agent_changed)
    {
        myDefinition = createDefinition(t);
        if (!myDefinition)
        {
            addError(SOP_MESSAGE, "Failed to create definition");
            return error();
        }
    }

    if (input_changed)
    {
        // Delete all the primitives, keeping only the points
        gdp->destroyPrimitives(gdp->getPrimitiveRange());

        // Create the agent primitives
        myPrims.clear();
        for (GA_Offset ptoff : gdp->getPointRange())
        {
            myPrims.append(GU_Agent::agent(*gdp, ptoff));
        }

        // Bumping these 2 attribute owners is what we need to do when adding
        // pack agent prims because it has a single vertex.
        gdp->getAttributes().bumpAllDataIds(GA_ATTRIB_VERTEX);
        gdp->getAttributes().bumpAllDataIds(GA_ATTRIB_PRIMITIVE);
        gdp->getPrimitiveList().bumpDataId(); // modified primitives
    }

    if (agent_changed || input_changed)
    {
        // Create a name attribute for the agents
        GA_RWHandleS name_attrib(gdp->addStringTuple(GA_ATTRIB_PRIMITIVE,
                                                     "name", 1));

        UT_Array<GU_AgentLayerConstPtr> current_layers;
        current_layers.append(
                myDefinition->layer(UTmakeUnsafeRef(GU_AGENT_LAYER_DEFAULT)));
        UT_Array<GU_AgentLayerConstPtr> collision_layers;
        collision_layers.append(
                myDefinition->layer(UTmakeUnsafeRef(GU_AGENT_LAYER_COLLISION)));

        // Set the agent definition to the agent prims
        UT_WorkBuffer name;
        UT_String agent_name;
        AGENTNAME(agent_name, t);
        int name_i = 0;
        for (GU_PrimPacked *pack : myPrims)
        {
            GU_Agent* agent = UTverify_cast<GU_Agent*>(pack->hardenImplementation());
            agent->setDefinition(pack, myDefinition);

            agent->setCurrentLayers(pack, current_layers);
            agent->setCollisionLayers(pack, collision_layers);

            // We only have 1 clip that can be used in the definition here.
            UT_StringArray clips;
            clips.append(myDefinition->clip(0).name());
            agent->setClipsByNames(pack, clips);

            // Convention for the agent primitive names is agentname_0,
            // agentname_1, agentname_2, etc.
            name.sprintf("%s_%d", agent_name.buffer(), name_i);
            name_attrib.set(pack->getMapOffset(), name.buffer());
            ++name_i;
        }

        // Mark what modified
        gdp->getPrimitiveList().bumpDataId();
        name_attrib.bumpDataId(); 
    }

    // Set the clip information for the agents. In general, agents can be set
    // to evaluate an blended array of clips to evaluated at a specific clip
    // offset.
    for (GU_PrimPacked *pack : myPrims)
    {
        GU_Agent* agent = UTverify_cast<GU_Agent*>(pack->hardenImplementation());
        agent->setClipTime(pack, /*clip index*/0, CLIPOFFSET(t));
    }
    gdp->getPrimitiveList().bumpDataId(); // we modified primitives

    return error();
}

// Provide input labels.
const char *
SOP_BouncyAgent::inputLabel(unsigned /*input_index*/) const
{
    return "Points to attach agents";
}