maj00r 951a54cde7 Bake only the ground a heightfield replaces, at a step suited to each triangle ...

Three changes to what goes into a baked heightfield and how it meets the geometry drawn
beside it.

The heightfield held every triangle laid in it, including those it does not replace and
that are therefore drawn as geometry too - so they were drawn twice, and a roof or a
bridge deck left in it bent the ground. Now the first pass lays everything and decides
what is replaced; the second lays the replaced triangles together with the neighbours
that support them - the owners of the corner samples of the cells around them, without
which those cells are not drawn - and only that is written. A first attempt that
repeated passes, dropping whatever bordered a hole, eroded the whole terrain away one
ring per pass: the edge of the ground is always a hole. The replaced triangles stay
replaced in the second pass, since their supports are all there and they have fewer
rivals. The triangles bake no longer keep in memory; they wait in a spill file beside
the heightfield while the scenery parses.

Triangles were refused for an edge longer than 200 m, meant for a water plane under the
whole map. On baltyk and tomaszewo that refused thousands of ordinary fields of a
hand-modelled terrain, and nothing there comes near a whole-map plane. Only triangles
standing on their edge - walls, trees, fences - are refused now. The bake log says why
the triangles not replaced are not: standing on edge, too small, under other surfaces,
next to a hole.

Hand-modelled terrain has triangles hundreds of metres long, elevation-model terrain
small ones along the line, and one grid step either loses the detail or samples a field
every metre. A bake now writes three heightfields a factor of four apart -
<scenario>.ehf, <scenario>.1.ehf, <scenario>.2.ehf - and each triangle goes to the
coarsest one that still puts sixteen samples along its longest edge, and to every
coarser one too, so the coarsest holds all the ground and a triangle at the edge of a
finer field can be replaced by a coarser field beneath it. All of them are picked up
together, and a missing or stale one sends the whole set to be baked again.

Where fields overlap each other or the geometry, the depth test decides: the terrain is
drawn with a polygon offset, negative for the reversed depth buffer and larger for each
coarser field, instead of being lowered by 2 cm - so geometry lying on the ground wins
at any distance and on any slope, and a finer field wins over a coarser one.

On tomaszewo the heightfields went from 176 MB to 10 MB, the load that bakes them from
5:16 to 3:11 and its peak memory from 15.7 GB to 8.5 GB - the scenery alone takes 8.0 -
while the triangles replaced went from 37,130 to 40,402. On baltyk from 19 MB to 2 MB,
with 6,670 triangles replaced against 4,040.

2026-09-17 17:24:25 +02:00

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