PickingBuffer

Remarks

Read back asynchronously, several frames later. Mapping a buffer the GPU may still be writing means waiting for the GPU, and doing that in the frame the click happened turns a click into a stall of however long the frame had left to run. The ring is Latency deep and a pick is resolved when its slot comes round again, by which time the copy has certainly landed.

⚠ One pixel is copied, not the target. A full-resolution R32 readback is sixteen megabytes a frame for a 4K viewport and answers a question about one pixel. The rectangle copied is the one the pointer is in — which is also why the picking pass can be skipped entirely on every frame nobody clicked.

The buffers are made once and kept. They are four bytes each; allocating one per click would put a device allocation on the click path, which is the one path where a hitch is felt as the tool being unresponsive.

Fields and properties (3)

• public int Latency

  How many frames a pick takes to come back.

• public PickRequest? Requested

  The pick waiting to be drawn this frame, if any.

• public static Int3 CopySize

  The size of the region copied out of the id target.

Methods (6)

• public PickingBuffer(IGraphicsDevice device, int latency = 3)

  Makes a ring of readback buffers.

• public long Request(int x, int y, bool additive = false)

  Asks what is under a point.

• public bool TryTakeRequest(out BufferHandle destination, out PickRequest request)

  The buffer this frame's copy should go into, if there is a copy to make.

• public bool Advance(out PickResult result)

  Moves to the next slot and answers whatever the one it lands on was asked.

• public void Abandon()

  Forgets every outstanding pick.

• public void Dispose()

  Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.

Used by (3)

• PickingRendererVixen.Editor.SceneView
• ScenePresenterVixen.Editor.App
• SceneViewportVixen.Editor.SceneView