User: "aren't some levels supposed to have fog?" -- they were, and none showed.
BTDPL.INI (the DPL env INI, L4DPLCFG) authors fog=near far r g b (+ often
nosearchlightfog=) on EVERY map/time/WEATHER leaf; weather is a fixed egg field
(clear/fog/soup). Shipped eggs pin cavern/night/clear -> page dsnitclear
(near 90, far 1100, dark blue). The env pipeline resolved + pushed it to D3D, but
it rendered INVISIBLE: D3DRS_FOGTABLEMODE=D3DFOG_LINEAR (table fog) derives its
factor from the perspective-NONLINEAR z-buffer, so without WFOG the 90..1100 range
collapsed to fog-factor ~1 (no fog everywhere).
Fix (L4VIDEO.cpp world pass): auto-detect D3DPRASTERCAPS_WFOG -> per-pixel W-fog
(smooth, == the arcade dpl_fog_type_pixel_lin); else VERTEX fog (eye-space but
per-vertex -> splotchy on coarse terrain tris, so only a fallback). FOGENABLE + the
fog mode are re-asserted each world-pass frame (the old one-time set got clobbered
per-pass, which is why plain table fog showed nothing). Verified on this GPU:
WFOG present -> per-pixel table fog, user-confirmed smooth.
Also corrected task #20's false "shipped maps define no fog" comment (it checked
.MAP/.RES, not BTDPL.INI). Env hooks: BT_FOGMODE=table|vertex|off, BT_WEATHER=
clear|fog|soup, BT_FOG="near far r g b" (now honored on the authored branch too);
[fog] resolved/model diagnostics. KB: rendering.md fog section added.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
