Working with data
Tensor
In Barracuda, Tensor values can be accessed using channels-last layout.
Four dimensional (or less) tensors should be prefered for performance reasons where possible. They can be accessed using batch, height, width, channels dimensions.
However up to 8 dimensional tensors are supported. The full set of supported dimensions is sequence, direction, batch, extraDimension, depth, height, width, channels.
Here is an exemple of Barracuda memory layout with a 4 dimensional NHWC tensor.
Note: The native ONNX data layout is channels-first. Barracuda automatically converts ONNX models to channel-last layout.
Data access
You can interact with Tensor data via multi-dimensional array operators:
var tensor4D = new Tensor(batchCount, height, width, channelCount);
// As N batches of 3 dimensional data: N x {H, W, C}
// ie accessing element at index [0,0,N,0,0,H,W,C] in this Tensor.
tensor4D[n, h, w, c] = 1.0f;
// As N batches of 1 dimensional data: N x {C}.
// ie accessing element at index [0,0,N,0,0,0,0,C] in this Tensor.
tensor4D[n, c] = 2.0f;
// As a flat array.
// accessing element at offset `index` in this Tensor.
tensor4D[ i] = 3.0f;
// Additionally for tensor with more than 4D dimension one can access data using:
var tensor8D = new Tensor(new TensorShape(sequence, direction, batchCount, time, depth, height, width, channelCount));
// As SxRxN batches of 5 dimensional data: SxRxN x {T, D, H, W, C}
// ie accessing element at index [S,R,N,T,D,H,W,C] in this Tensor.
tensor8D[s, r , n, t, d, h, w, c] = 1.0f;
// As N batches of 4 dimensional data: N x {D, H, W, C}
// ie accessing element at index [0,0,N,0,D,H,W,C] in this Tensor.
tensor8D[n, d, h, w, c] = 1.0f;
Constructor
Multiple Tensor constructors cover a variety of scenarios up to 8 dimensions. By default tensors initialize with 0 upon construction, unless you provide an initialization Array:
// batch of 1 dimensional data, 0 initialized: batchCount x {elementCount}
tensor = new Tensor(batchCount, elementCount);
// batch of 3 dimensional data, 0 initialized: batchCount x {height, width, channelCount}
tensor = new Tensor(batchCount, height, width, channelCount);
// sequence * direction * batch of 5 dimensional data, 0 initialized: sequence * direction * batchCount x {time, depth, height, width, channelCount}
tensor = new Tensor(new TensorShape(sequence, direction, batchCount, time, depth, height, width, channelCount));
var stridedArray = new float[batchCount * elementCount] { ... };
// batch of 1 dimensional data, initialized from strided array
tensor = new Tensor(batchCount, elementCount, stridedArray);
var jaggedArray = new float[batchCount][elementCount] { ... };
// batch of 1 dimensional data, initialized from jagged array
tensor = new Tensor(batchCount, elementCount, jaggedArray);
Texture2D texture = ...;
// tensor initialized with texture data: 1 x { texture.width, texture.height, 3}
tensor = new Tensor(texture);
You can query the shape of the Tensor object, but you cannot change the shape of the Tensor. If you need a different shape of Tensor, you must construct a new instance of the Tensor object:
var shape = tensor.shape;
Debug.Log(shape + " or " + shape.sequenceLength + shape.numberOfDirections + shape.batch + shape.extraDimension + shape.depth +shape.height + shape.width + shape.channels);
Texture constructor
You can create a Tensor from an input Texture or save a Tensor to a Texture directly.
Note: When you do this, pixel values are in the range [0,1]. Convert data accordingly if your network is expecting values between [0,255], for example.
Texture as input
You can directly pass Texture2D, Texture2DArray, Texture3D or RenderTexture to Barracuda without accessing individual pixels on the CPU:
// you can treat input pixels as 1 (grayscale), 3 (color) or 4 (color with alpha) channels
var channelCount = 3;
var tensor = new Tensor(texture, channelCount);
You can batch multiple textures into the single Tensor object:
// these textures form a batch
var textures = new [] { texture0, texture1, texture2, texture3 };
var tensor = new Tensor(textures, channelCount);
Note: All textures in a batch must have the same width and height dimensions.
Texture as output
If you want to use Barracuda execution results further in the graphics pipeline, you can copy data from Tensor into a RenderTexture without stalling the CPU or GPU:
var tensor = worker.PeekOutput();
var texture = BarracudaTextureUtils.TensorToRenderTexture(tensor);
You can reuse the same RenderTexture multiple times:
var texture = new RenderTexture(width, height, 0);
// ...
tensor = worker.PeekOutput();
BarracudaTextureUtils.TensorToRenderTexture(tensor, texture);
Cleanup
As a Barracuda user you are responsible for calling Dispose() on inputs, outputs and any data that you created, received via worker.Fetch() or have taken ownership of by calling tensor.TakeOwnership().
Note: This is necessary to free up GPU resources properly.
tensor.Dispose();
Note: You do not need to call Dispose() on tensors that you received via the worker.PeekOutput() call.