The crater shader ran on every pixel of a fullscreen rect every frame and
was by far the most expensive thing in the surface scene. Nothing else came
close: RockField keeps 14 rocks alive, Rock/Ship/Enemy already avoid
per-frame queue_redraw() for transform-only changes, and LunarBackground.gd
is a handful of scalar ops.
Three reductions to the field itself:
- 5x5 -> 3x3 neighbour scan. That width was never the geometric answer;
it was insurance against craters seen clipping at cell boundaries
on-device, i.e. a crater reaching past its nominal radius because a hash
returned a value outside [0,1] and extrapolated mix(). Clamping the
crater CENTRE into its own cell, alongside the radius clamp already
there, bounds the reach whatever the hash returns - so a crater two cells
out is >= 1.0 cells away, a normalized distance of >= 2.63, past every
threshold the shading reacts to (the last saturates at 1.15). The outer
ring provably cannot change a pixel. This removes the clipping bug's
cause instead of hiding it behind 16 extra samples.
- One hash42 per cell instead of hash21 twice plus hash22, decorrelating
on output lanes rather than input offsets.
- Squared distances in the loop, square-rooted twice at the end rather
than once per sample.
Measured with the new tests/profile_shader.sh, above softpipe's own ~657ms
fullscreen floor: 9482ms -> 405ms of shader work, a 23x reduction.
Then the larger change: the field is a fixed function of world position, so
every frame recomputed an identical answer. It is now made periodic (the
cell index is wrapped before hashing, which makes a Worley field tile
exactly rather than merely blend), baked once at load into one tile, and
scrolled with repeat wrapping by lunar_tiled.gdshader - one texture fetch
per pixel. Two honest costs: the field repeats every 7040 world units, and
a fixed-resolution tile softens when zoomed past 1:1. Lunar regolith is
forgiving of both, having no landmarks and being smooth gradients already.
The bake waits a frame and asks the material whether it actually samples a
field_texture, so a gas giant - which swaps in its own background shader
(#51) - does not pay for a 2048-square tile it will never read. Headless
runs skip it entirely, having nothing to rasterize.
tests/test_lunar_field.gd guards the reasoning, since a fragment shader
cannot be asserted on directly: the premises are still in the source, the
worst-case ring-2 geometry stays clear of every threshold independent of
the hash, a 3x3 and a 5x5 scan render identically over 4000 sampled points,
the field repeats exactly in both axes, and the miss sentinel still cannot
overflow mediump into +Inf and then NaN.
test_surface_profiles.gd asserted "a rocky landing leaves the background
alone" by naming lunar_surface.gdshader; it now reads the shader from the
scene, which is the property it actually cares about.
PlanetSurface.tscn's edit also carries the planet-name relocation described
in the HUD commit - same scene file, so the two cannot be split.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Loïc Wisniewski