After the round-star fix, toggling "Anti-aliased stars" made stars look
bigger and more numerous instead of just smoother. The AA path differed
from the hard-edge path in three ways that each inflated the footprint:
- radius: AA used 0.25 + b*0.4 (up to 0.65); hard path used fixed 0.5
- gain: AA used 4.0; hard path used 3.0 (+33% peak brightness)
- falloff: AA Gaussian decayed slowly (36.8% at one radius, never 0);
hard path smoothstep hit 0 at the radius
The slow Gaussian tail was the main offender: it kept dim stars lit far
past the hard path's cutoff, lifting many sub-threshold stars above the
visibility floor — the apparent "more stars".
Balance the two paths so the toggle is purely an edge-softness control:
- both use radius = 0.25 + b*0.4 (same size, brightness-driven)
- both use gain 3.0 (same peak brightness)
- AA steepens the Gaussian to exp(-4.6*d²/r²) so it converges to ~1%
near the same radius where smoothstep cuts to 0 — matched footprint,
soft vs hard edge.
Peak brightness is now identical across the toggle; effective lit area
differs by <30% (the Gaussian is a cone, smoothstep a flatter dome) and
the visibility radius matches, so dim stars no longer pop in and out as
AA is toggled.
Validated: naga type-checks; app runs 20s on Metal (M4) with no shader
errors; cargo test (14 physics tests) passes.
xfy
52cf4e4a29