The features added in Rounds A–D were correct but expensive. The hot
path per frame was sky_color() called from apply_fog for EVERY distant
pixel — 4-octave cloud fbm + star hash + sun/moon disc per fragment,
hundreds of thousands of pixels per frame. Profile-driven cuts that
keep all features but stop paying for them in the wrong places:
1. apply_fog now mixes terrain toward sky_dome (cheap gradient) not
sky_color (gradient + clouds + sun + moon + stars). Distant terrain
still fades to the right-direction sky color at every time of day;
the per-pixel cost drops by ~80%. Full sky_color still runs for
the SKY BACKGROUND pass where it's actually paid for.
2. Sky pipeline draws AFTER terrain with depth_compare = LessEqual.
The full-screen sky was previously written first then over-painted
by terrain — sky's expensive fragment shader ran on every screen
pixel. Now it only runs on pixels with no terrain in front of them
(depth = 1.0 cleared), which on most views is 30–60% of the screen
instead of 100%.
3. fbm2 reduced from 4 → 3 octaves. Negligible visual change at the
scales we sample, ~25% cheaper per cloud-pixel.
4. Cloud branch skips entirely when day_strength < 0.05 (full night).
Clouds invisible at night anyway, fbm + smoothstep + mix skipped.
5. In-game FPS HUD (top-right corner):
- Telemetry struct gains frame_dt_ms (EMA-smoothed in app.rs
with coefficient 0.85 so the number is readable, not flickery).
- wasm bridge: get_frame_dt_ms().
- main.js setupFpsHud() polls it at 5Hz, color-coded:
green ≤ 18ms (≥55fps), amber 18-33ms, red beyond.
- Reads what THE GAME measures, not the browser's
requestAnimationFrame which gets throttled to 1 Hz on
unfocused windows.
No features removed. God rays, FXAA, ACES tonemap, bounce baking,
specular materials, leaf translucency — all still there. Tests:
63 passing. Wasm release clean.
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