[nolanbaxter]

Faster where it was slow, measured. A speed audit of the engine against other engines'
techniques, each change A/B'd on Sponza, a million splats or 100,000 objects before it was
kept: splats too small to see are left out, the sun's shadows stay cached while the camera
moves, a frame where a few things move touches only those, and crowded lights shade faster.
Drawing tiny particles as points was measured slower and dropped.

Added

• Splats too faint and small to show are left out. renderer.splatCull
  (default 0.5): a splat whose opacity times the pixels it covers is under it is left out of the
  sort and the draw, which a sub-pixel splat costs a quad of all the same. A million splats seen
  whole at 720p on Iris Xe: 27.4 -> 16.8 ms, 0.06% of channels moved by more than 8 levels; a
  capture seen close: unchanged. 0 draws every splat as before.

Changed

• The sun's shadows are redrawn far less while the camera moves. A cascade's box was snapped
  to whole texels and its depth range not at all, so a moving camera made a new matrix -- and a
  redraw -- for every cascade nearly every frame. Snapped to a 16-texel grid, depth included, with
  a grid step of margin, a cascade holds still until the camera has moved that far, and the cache
  keeps it. Sponza at 720p on Iris Xe, camera moving: cascades redrawn 4.00 -> 0.38 a frame, GPU
  10.7 -> 6.2 ms. Texels are 1.5% larger. Anything moving inside a cascade still redraws it at once.
• A frame where a few things move no longer looks at everything that didn't. Composing
  transforms, updating world boxes, the scene's extent and the draw-data upload each walked every
  node or renderable to find the ones that moved. The transform store now lists what was marked
  dirty and what moved, composing those and their subtrees, and the rest follow the list. The
  extent is grown by the boxes that moved, recomputed whole only when one leaves a face of it.
  100,000 objects with 2 moving: CPU 2.3 -> 1.2 ms a frame (transforms 0.41 -> 0.02, draw data
  0.58 -> 0.06, bounds 0.77 -> 0.3). Past 4,096 movers, or an eighth of the nodes, it is the
  whole pass as before.
• Many overlapping lights cost less to shade. Profiled, most of their cost was walking each
  cell's light list rather than shading: every light was two loads, the second waiting on the
  first. Lights are now read four at a time, their indices and then their positions, before any
  is tested. 256 lights in Sponza at 720p on Iris Xe, forward pass: 17.3 -> 14.1 ms at 3 m radius,
  10.0 -> 8.9 ms at 2 m, unchanged at 1 m and with few lights. The picture is the same.

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npm install winding-engine

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