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sky(phase-5b): port retail vertex fog onto sky meshes

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Retail applies linear vertex fog with 3D range distance
(D3DRS_FOGVERTEXMODE=3=LINEAR, D3DRS_RANGEFOGENABLE=1,
D3DRS_FOGTABLEMODE=0=NONE) to ALL mesh draws including sky. Only
FOGCOLOR / FOGSTART / FOGEND are lerped per keyframe; the mode flags
are init-only.

Verified in `docs/research/2026-04-23-sky-fog.md`:
  - chunk_005A0000.c:3361-3389 device-init sets the modes.
  - Sky meshes render at world origin (translation zeroed, rotation-
    only) with intrinsic mesh radii in the thousands of meters
    (WorldBuilder's SkyboxRenderManager.cs:247 comment confirms).
  - With keyframe MaxWorldFog = 2400m, the dome saturates to
    WorldFogColor at its horizon band. THAT is retail's dusk/dawn
    horizon-glow mechanism.

Port:

`sky.vert` now computes the vertex fog factor:
    worldPos = uModel × aPos         (camera-centered since view translation=0)
    dist = length(worldPos.xyz)
    fogFactor = clamp((fogEnd - dist) / (fogEnd - fogStart), 0, 1)
  — outputs as varying vFogFactor. 1.0 means no fog contribution,
  0.0 means full fog color.

`sky.frag` applies the mix BEFORE the lightning-flash bump:
    rgb = mix(uFogColor.rgb, rgb, vFogFactor)

Uses the existing SceneLighting UBO's uFogParams (x=start, y=end,
z=flash, w=mode) and uFogColor — no new uniforms, no C# change.

Expected visual:
  - Dome at dawn/dusk: horizon band blends toward keyframe fogColor
    (warm orange at sunset, cool blue at dawn), matching retail's
    sky/fog coupling.
  - Close sky objects (sun disk at typical mesh radius): unaffected
    since dist < fogStart.
  - Clouds at intermediate distance: partial fog blend, subtly
    muting their saturation with distance.

Note on lightning: the flash channel (uFogParams.z) stays wired but
is currently always 0 because no code drives it. Agent #5 is
researching retail's real lightning mechanism (PlayScript / SetLight
PhysicsScript / other). This commit does not attempt to port it.

Build + 733 tests green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-24 11:06:57 +02:00
parent 53608e77e3
commit 8a42750459
2 changed files with 61 additions and 9 deletions
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30
src/AcDream.App/Rendering/Shaders/sky.frag
View file

@ -16,16 +16,18 @@
//
// See `docs/research/2026-04-23-sky-material-state.md`.
in vec2 vTex;
in vec3 vTint;
in vec2 vTex;
in vec3 vTint;
in float vFogFactor; // 1 = no fog (near), 0 = full fog color (far)
out vec4 fragColor;
uniform sampler2D uDiffuse;
uniform float uTransparency; // 0 = fully visible, 1 = fully transparent
uniform float uLuminosity; // SkyObjectReplace.Luminosity override (0..1)
// Shared SceneLighting UBO — only need the fog-flash channel for
// client-driven lightning strobes; sun/ambient already baked into vTint.
// Shared SceneLighting UBO — fog params drive the mix, flash channel
// bumps sky brightness during lightning strikes. Matches sky.vert's
// declaration exactly.
struct Light {
vec4 posAndKind;
vec4 dirAndRange;
@ -46,14 +48,24 @@ void main() {
// Composite: texture × per-vertex lit × per-keyframe dim.
vec3 rgb = sampled.rgb * vTint * uLuminosity;
// Lightning additive bump (client-driven during storm keyframes).
// Retail vertex fog: lerp(fogColor, scene, fogFactor). At distant
// horizon dome vertices (distance > FOGEND) the sky saturates to
// the keyframe's WorldFogColor — that's retail's horizon-glow
// mechanism at dusk/dawn. See docs/research/2026-04-23-sky-fog.md.
rgb = mix(uFogColor.rgb, rgb, vFogFactor);
// Lightning additive bump — client-driven during storm flashes.
// NOTE: the exact retail mechanism for lightning visual is still
// under research (agent #5, 2026-04-23). Keeping the uFogParams.z
// channel wired so if it ends up being a per-frame flash uniform
// that's what it becomes; if lightning turns out to be a particle
// system effect instead, this bump becomes a no-op (flash stays 0).
float flash = uFogParams.z;
rgb += flash * vec3(1.5, 1.5, 1.8);
// Normal-frame cap at 1.0 (retail D3D framebuffer clamps at 1.0
// per channel for RGBA8 output; vTint is already vertex-clamped so
// the only path above 1 is lightning flash additive bump). During
// a flash the ceiling relaxes so the strobe blows out visibly.
// Normal-frame cap at 1.0 (retail D3D framebuffer clamps per-channel
// on output). Flash relaxes ceiling to 3.0 so storm strobes blow
// out visibly.
float cap = mix(1.0, 3.0, clamp(flash, 0.0, 1.0));
rgb = min(rgb, vec3(cap));