Release 1.6.0: fewer draws, less overdraw, shadows that scroll

[nolanbaxter]

Fewer draws, less overdraw, shadows that scroll. Every mesh's geometry now lives in one
arena, and every mesh drawn once is pooled with the others of its material into one draw; the
sun's shadow maps scroll with the camera instead of being redrawn; shadow passes read positions
alone; and the merged meshes draw their depth before they shade. Each change A/B'd before it was
kept, with the same pixels. On Iris Xe at 720p: Sponza 4.64 -> 4.15 ms a frame, 256 point lights
9.17 -> 6.64 ms, a town of 900 separate buildings 14.8 -> 4.0 ms of GPU.

Changed

• Merged meshes draw their depth first. With no depth prepass, a pixel's cost depended on draw
  order: a surface drawn before the wall in front of it was shaded and then covered. The opaque
  merged groups now draw depth alone first, and then shade only where they match it, so every
  pixel they cover shades once, whatever the order; other opaque meshes test against that depth
  too. Sponza walking the nave: main pass -19%, GPU -16%; with 256 point lights, the main pass
  -29% to -34%. A town of 900 buildings, one group: no measurable cost. The same pixels, but for
  one in 900,000 where two surfaces meet at exactly equal depth. GPUs that hide overdraw in
  hardware (Apple's) gain nothing from it and pay its depth draw; unmeasured.
• Shadow passes read positions alone. The geometry arena keeps every vertex's position a
  second time, by itself, and a depth-only shadow draw reads those 12 bytes instead of the whole
  60-byte vertex. Sponza under a turning sun, every cascade redrawn each frame: shadow passes -10%.
  The same pixels; vertex memory +20%.
• Big meshes are drawn a chunk at a time. Each mesh's triangles are boxed in runs of 128 at
  load. A strip of a scrolled shadow cascade draws only a mesh's chunks that reach it -- a strip
  is thin, and its cost was every vertex of every mesh it touched -- and a merged mesh's chunks
  out of view are dropped from the camera's draw as its whole was. Sponza walking the nave, against
  the last change: GPU -8%, the nearest cascade's strips 0.49 -> 0.18 ms; the same pixels.
• Their shadows too, when a shadow map is drawn whole. Each material's merged meshes also
  keep a list of every one's triangles, copied once, and a shadow view drawn whole -- a cascade
  under a turning sun, a point or spot light's -- is a draw per material rather than per mesh.
  A strip of a scrolled cascade stays mesh by mesh, where culling each mesh to the strip skips
  more. A town of 900 buildings under a turning sun: frame 17.9 -> 10.1 ms, CPU 2.4 -> 0.9 ms.
• Meshes drawn once each share one draw call per material. A scene of distinct meshes -- a
  level, Sponza, a town of separate buildings -- was a draw call per mesh, and each costs the GPU
  about 7 us whether it draws anything or not. Now every mesh part drawn once is pooled with the
  others of its material into one indexed draw, its vertices read straight from the geometry arena;
  a part out of view keeps its place as triangles of one repeated vertex, which the GPU discards,
  and only a part that comes into view or leaves it is rewritten. A town of 900 buildings: 900
  draws -> 1, GPU 14.8 -> 4.0 ms, frame 23.3 -> 9.6 ms; Sponza: 103 draws -> 25, GPU -14%. The same
  pixels. These parts are culled to the view, not by occlusion; meshes drawn many times are drawn
  instanced, as before. stats.draws counts the calls.
• Every mesh's geometry lives in one arena. One vertex buffer and one index buffer for every
  primitive loaded, where each had its own; a pass binds them once instead of per batch, and a
  freed range is reused by the next load. Groundwork for drawing many meshes in one call.
• Identical materials are one material. A material identical to one already loaded -- every
  factor but its name, and the same textures -- shares its id, so the same asset loaded many
  times is one material, not one each. A material an animation drives is never shared.
• Off means off: bloom at strength 0 draws none of its passes. A strength of 0 mixed no bloom
  in, but its nine passes were drawn all the same: 0.36 ms a frame at 720p on Iris Xe.
• A scene with no point or spot lights skips their loop. The shader that loops over them is
  compiled out, in pipelines built in the background the first time such a scene draws; until then
  it draws with the loop, as before. Sponza with only the sun: forward pass 5% faster.
• A moving camera scrolls the sun's shadow maps instead of redrawing them. When a cascade's box
  steps along its grid and nothing else changed, its map keeps every texel where it is -- the map
  wraps, and only its origin moves -- and only the strip the box moved onto is drawn. The same
  shadows: a scrolled map matches one drawn whole to within a level on a few dozen channels.
  Sponza at 720p on Iris Xe, walking the nave: shadow passes 3.9 -> 0.55 ms a frame, the whole
  frame 11.9 -> 7.6 ms. The new stats.cascadesScrolled counts them.
• Every caster in the scene casts into every cascade. A cascade's depth now spans the scene
  along the light, rather than reaching four cascade radii toward it -- so a tall building far up
  the light no longer loses its shadow -- and stays put while the camera moves, which is what
  lets a cascade scroll. casterExtent is deprecated and no
  longer used.
• Each sun cascade draws only the casters that reach it. Every caster went into every cascade,
  to be transformed and clipped away by the GPU; now a batch whose box lies outside a cascade is
  not drawn into it. The same shadows. A town of 900 separate buildings: shadow passes 0.40 ->
  0.22 ms a frame. Sponza, whose cost is a few large meshes every cascade reaches, is unchanged.

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npm install winding-engine

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