The noise is evaluated at vec3(xz * f, c), so .z is the slope along the held
constant axis. Confirmed numerically (harness/scene/gradAxis.cjs): analytic
.xy matches central differences for fbm and phacelle, .z does not. Only the
ray-march scene's normals were affected; the grid tier already used .xy.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
trace: steps per pixel and pass ms at three fixed camera poses, PREPASS=0,1 arms.
diff: one frozen frame with and without the prepass, against a 512-step render.
bundle.cjs demo: full-window page with a prepass switch and the readout.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Pass 1 sphere-traces CultMath noise terrain (fbm plus Phacelle erosion) and the
world tree with a conservative Lipschitz step, writing colour and depth. Pass 2
marches fog and clouds only up to that depth at low resolution with TAA. The
camera pulls back from the tree on login. Vendors CultLib's generated GLSL
(658c09e). The Phacelle gradient bound is an empirical probe, not a proof.
Headless harness compiles, renders and times it; nothing run on a GPU.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
