Explore USD tools and rendering

% python usdzconvert --help
usdzconvert 0.66
usage: usdzconvert inputFile [outputFile]
                   [-h] [-version] [-f file] [-v]
                   [-path path[+path2[...]]]
                   [-url url]
                   [-copyright copyright]
                   [-copytextures]
                   [-metersPerUnit value]
                   // ...
                   [-diffuseColor           r,g,b]
                   [-diffuseColor           <file> fr,fg,fb]
                   [-normal                 x,y,z]
                   [-normal                 <file> fx,fy,fz]
                   // ...

// asset.usda
#usda 1.0
(
    customLayerData = {
        dictionary Apple = {
             int preferredIblVersion = 2
        }
    }
)

// Rosetta
% arch -x86_64 /bin/zsh

// Download source code
% git clone https://github.com/PixarAnimationStudios/USD.git 

// Build USD + Hydra
% python3 USD/build_scripts/build_usd.py --generator Xcode --no-python USDInstall

// AAPLViewController.mm

- (void)viewDidAppear
{   
    NSOpenPanel* panel = [NSOpenPanel openPanel];
    panel.allowedContentTypes = @[UTTypeUSD, UTTypeUSDZ];
   
    [panel beginWithCompletionHandler:^(NSModalResponse result) {
        if (result == NSModalResponseOK)
        {
            NSURL* url = panel.URLs[0];
            [self->_renderer setupScene:[url path]];
        }
    }];
}

// AAPLRenderer.mm

- (bool)loadStage:(NSString*)filePath
{
    _stage = UsdStage::Open([filePath UTF8String]);
    // ...
}

// AAPLRenderer.mm

- (void)setupCamera
{
    _viewCamera = [[AAPLCamera alloc] initWithRenderer:self];
    
    [self calculateWorldCenterAndSize];
    
    [_viewCamera setDistance:_worldSize];
    [_viewCamera setFocus:_worldCenter];

}

// AAPLRenderer.mm

GlfSimpleLight computeCameraLight(const GfMatrix4d& cameraTransform)
{
    GlfSimpleLight light;
    light.SetPosition(GfVec4f(cameraPosition[0], cameraPosition[1], cameraPosition[2], 1));
    
    return light;
}

// AAPLRenderer.mm

- (void)initializeEngine
{
    _engine.reset(new UsdImagingGLEngine(_stage->GetPseudoRoot().GetPath(),
                                         excludedPaths,
                                         SdfPathVector(),
                                         SdfPath::AbsoluteRootPath(),
                                         driver));
}

// AAPLRenderer.mm

- (HgiTextureHandle)drawWithHydraAt:(double)timeCode
                           viewSize:(CGSize)viewSize
{
      _engine->SetCameraState(modelViewMatrix, projMatrix);
      _engine->SetLightingState(lights, _material, _sceneAmbient);
  
      UsdImagingGLRenderParams params;
      params.clearColor = GfVec4f(0.0f, 0.0f, 0.0f, 0.0f);
      params.frame = timeCode;

      // ... 
}