Moppe is evidence, a tuning library, and a legacy #C4XGYX

Moppe (~/src/moppe) is the predecessor engine: a C++/Metal terrain world with a complete cinematic renderer. It proves an ambitious end state on the actual development machines, preserves hundreds of tuned judgment calls, and shows what luv should improve: its answers are frozen in MSL and duplicated by convention, where luv can hold shared material meaning as live Lisp objects.

This page now stays a source-study and transplant inventory. The native backend motivation it originally contained has become executable luv work and moved, with its stable figure IDs, to the native Metal 4 backend. Read Moppe as #H7QK3M advises: observed mechanism, source claim, and luv's possible choice are different voices.

Mentioned in: Where luv's semantic arithmetic goes beyond its sources

The post stack reveals what finished-looking means #8VA1EX

moppe/shaders/metal/post.metal supplies a concrete observed sequence:

1. Auto-exposure averages wide HDR taps into a tiny CPU-read target and adapts one exposure scalar. Bloom sees the exposed scene.
2. Bloom uses a soft-knee bright pass and quarter-resolution chain; a smoothstep (0.85, 1.35, luma) threshold and five-sample linear-filter trick evaluate the nine-tap Gaussian cheaply.
3. Lens character adds edge-gated chromatic fringe, veil, anamorphic streak, and sun ghosts modulated by visibility.
4. ACES tonemap converts the linear scene, followed by sRGB encoding.
5. Color grade applies warm print-film CDL, split tone, vibrance, grain, and vignette.
6. EDR output re-linearizes and permits true highlights above diffuse white within current display headroom.

The sequence matters more than any individual effect: exposure and tone mapping establish the medium in which bloom and grade make sense. #SKHDR already follows that order. Moppe's grade is especially attractive because it is cheap, separable, and made of constants which can become live uniforms or hot-redefined material methods.

Mentioned in: Logarithmic quantities as affine structure

Sun shafts are the highest-glamour transplant #BAP0QU

Moppe's shafts_gather_fragment marches view rays at half resolution through the existing shadow map, jitters them with interleaved-gradient noise, stops at scene depth, and weights lit spans by a forward Henyey-Greenstein lobe with g = 0.60. A separate pass filters and adds the result.

Luvcraft already owns both inputs: a stored shadow map (#2WX9PW) and offscreen scene depth. The effect needs no new world representation. It does need the linear-HDR target (#WLHDRB) so gathered light adds in meaningful units.

Mentioned in: Transplant the post stack onto the HDR path, March the shadow map for shafts and compare against the screen sweep, One arithmetic medium, many clients, What the presentation stack became

common.h is a library of judgment calls #094ZB1

moppe/shaders/metal/common.h is valuable less for novel algorithms than for tuning worth testing:

• moppe_hemisphere_light splits ambient into warm ground bounce and cool sky;
• moppe_warmed_fog couples fog colour to forward and backward solar lobes;
• moppe_sky_radiance supplies a cheap analytic reflected environment;
• moppe_sun_visibility records centre-weighted PCF, response shaping, and distance fade, including the observed pow 1.3 response;
• moppe_cloud_transmission projects stable cloud shadow onto world points; and
• coupled gust, bough, and flutter clocks coordinate foliage motion.

The strongest argument for re-expressing these in luv is duplication. The daylight / golden pair is recomputed independently in several shaders. In luv it can be one shader abstraction (#DXYHT4) reused with shared meaning and one live redefinition point.

Sky, temporal reconstruction, and mesh shaders bound the proof #KK6M0T

Three larger observations describe capabilities rather than immediate ports:

• sky.metal combines a three-stop atmosphere, golden-hour band, Mie lobes, two cloud layers, stars, dithering, and a fog-matched horizon. Luvcraft's smaller sky (#SKDYCY) has the same conceptual shape.
• Scene shaders emit motion vectors and a reactive mask for MetalFX temporal reconstruction. This records a heavier answer if local filtering no longer controls temporal shimmer.
• The forest shadow pass is a native Metal object + mesh shader pipeline. It proves the hardware capability while MoltenVK cannot expose the same route. That observation originally motivated #NABRMK; the resulting luv backend and its remaining shader join now live on the Metal page.

These are forcing examples, not reasons to import Moppe's renderer wholesale. The post stack is largely backend-neutral fullscreen work, while mesh stages should enter luv's shader language only when a concrete native pipeline makes their types and interfaces precise.