# Scene Importer & Exporter

The Simplygon API provides classes for loading and saving various scene file formats. Currently the supported format are

Alembic (.abc)
FBX (.fbx)
glTF (.gltf, .glb)
Houdini geometry (.bgeo)
OBJ (.obj)
Simplygon (.sg)
USD (.usd, .usdc, .usda)

# Importing

Importing scene data is done by the ISceneImporter class. The file information is then stored in an IScene, where both the geometries, materials and textures of the imported file can be found.

void LoadScene( const char* readFrom )
{
    spSceneImporter importer = sg->CreateSceneImporter();
    spScene scene;

    // Set the path of the file to load
    importer->SetImportFilePath( readFrom );
    if( importer->RunImport() )
    {
        scene = importer->GetScene();
    }
    // do stuff with scene
}

# Exporting

Exporting scene data is done by the ISceneExporter class. The file format is determined by the file name extension.

If the file name does not contain a known supported file extension (see list above) it will output the internal Simplygon binary scene dump format (same as if you export a file with .sg extension), which can then be read by the scene importer. This is useful for integrating the batch tool into your data pipeline or when requesting support, as it contains an exact representation of the Simplygon scene data.

void SaveScene( const char* fileName, spScene scene )
{
    spSceneExporter exporter = sg->CreateSceneExporter();
    exporter->SetScene( scene );
    exporter->SetExportFilePath( fileName );
    
    // For file formats that only supports a limited set of texture coordinate layers,
    // set the name of the primary layer to export
    exporter->SetPrimaryTexCoordName( "tex0" );

    // Some file formats support embedding texture and other data in the main scene file.
    // This flag controls if such data will be embedded or written to separate files
    exporter->SetEmbedReferences( true );

    // Some file formats  support exporting cascaded scenes in the same file.
    // This flag controls if cascaded scenes will be written or ignored
    exporter->SetExportCascadedScenes( true );

    exporter->RunExport();
}

void SaveScene( string fileName, spScene scene )
{
    spSceneExporter exporter = sg.CreateSceneExporter();
    exporter.SetScene( scene );
    exporter.SetExportFilePath( fileName );
    
    // For file formats that only supports a limited set of texture coordinate layers,
    // set the name of the primary layer to export
    exporter.SetPrimaryTexCoordName( "tex0" );

    // Some file formats that support embedding texture and other data in the main scene
    // file, this flag controls if such data will be embedded or written to separate files
    exporter.SetEmbedReferences( true );

    // Some file formats  support exporting cascaded scenes in the same file.
    // This flag controls if cascaded scenes will be written or ignored
    exporter.SetExportCascadedScenes( true );

    exporter.RunExport();
}

def SaveScene( fileName, scene ):
{
    exporter = sg.CreateSceneExporter()
    exporter.SetScene( scene )
    exporter.SetExportFilePath( fileName )
    
    # For file formats that only supports a limited set of texture coordinate layers,
    # set the name of the primary layer to export
    exporter.SetPrimaryTexCoordName( "tex0" )

    # Some file formats that support embedding texture and other data in the main scene
    # file, this flag controls if such data will be embedded or written to separate files
    exporter.SetEmbedReferences( True )

    # Some file formats  support exporting cascaded scenes in the same file.
    # This flag controls if cascaded scenes will be written or ignored
    exporter.SetExportCascadedScenes( True );

    exporter.RunExport()
}

# Cascaded scenes

You can output all cascaded scenes when exporting by setting the export cascaded scene flag with a call to SetExportCascadedScenes function. Note that all file format does not fully support cascaded scenes.

# Limitations

Currently there are a number of limitations to features supported in the various file formats

# FBX

Bone data and skinned meshes are not supported
Selection sets are not supported
There is limited support for blend modes and custom materials/shaders
Due to limitations in the FBX SDK, all importer & exporter calls will be limited to one concurrent thread
The FBX format can only contain one scene per file. Cascaded scene output will be converted into top-level nodes in the FBX scenes, one per cascaded scene in a depth-first pattern.
Transforms on the root FBX node will be emulated with an inserted node at the top of the Simplygon scene hierarchy

# glTF

Different sampler wrap modes in S/T directions are not supported, S direction is used for both directions
Cascaded scenes are output as separate glTF scenes in a depth-first pattern, with the top level scene set as the default glTF scene.

# Extensions

KHR_texture_transform is supported
Any other required extensions will result in an error
All other optional extensions are ignored

# OBJ

Cascaded scenes are not supported
Bone data and skinned meshes are not supported

# USD

Only the UsdPreviewSurface material model is supported
Blend shapes not supported

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