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feat(sky): split SkyRenderer into pre-/post-scene passes + retail -120m weather Z offset

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Bug A (foreground rain) from docs/research/2026-04-26-sky-investigation-handoff.md:
rain mesh was only visible at horizon, not in the air between camera and
character. Two retail mechanisms ported here:

1. **Render order split.** Retail's `LScape::draw` at 0x00506330 calls
   `GameSky::Draw(0)` BEFORE the landblock DrawBlock loop and
   `GameSky::Draw(1)` AFTER — i.e. weather meshes render after scene
   geometry so additive rain streaks paint on top of terrain and entities.
   Acdream was rendering both passes pre-scene, so terrain immediately
   painted over the rain.

   Refactored `SkyRenderer.Render` into `RenderSky` (filter !IsWeather)
   and `RenderWeather` (filter IsWeather) sharing a private `RenderPass`
   core that takes a `weatherPass` bool. Partition is per-SkyObject by
   `Properties & 0x04` (the WEATHER_BIT, mirroring tools/WeatherEnumerator).
   Added `SkyObjectData.IsWeather` getter for the partition.

   `GameWindow.OnRender` now calls `RenderSky` before terrain/static-mesh/
   particles (line ~4322) and `RenderWeather` after particles (line ~4368).

2. **Weather Z offset.** Retail `GameSky::UpdatePosition` at 0x00506dd0,
   lines 0x506e96..0x506e98:

       if (((eax_13 & 4) != 0 && (eax_13 & 8) == 0))
           int32_t var_4_1 = 0xc2f00000;   // 0xc2f00000 == -120.0f

   Weather objects (property bit 0x04 set, bit 0x08 unset) get their frame
   origin set to player_pos + (0, 0, -120m). The rain cylinder GfxObjs
   0x01004C42/0x01004C44 have local Z range 0.11..814.90 (815m tall, 113m
   radius). Without the offset the cylinder bottom sat just above the
   camera; with -120m the cylinder spans (camera-119.89)..(camera+694.90)
   so the camera is inside.

   `SkyRenderer.RenderPass` applies the -120m model translation when
   `weatherPass` is true (line ~253-254).

3. **Legacy camera-attached emitter gated.** `UpdateWeatherParticles` —
   the pre-research workaround that emitted camera-attached rain particles
   (broken alpha fade, fixed disk around camera) — is now gated behind
   `ACDREAM_FAKE_RAIN_PARTICLES=1`. Default off; the retail-faithful
   world-space mesh is the default path.

User-verified: rain is now visible in foreground from many perspectives,
but the cylinder's open-top rim is still visible when looking straight up.
That rim issue is a separate brightness-excess bug filed for follow-up
(Translucency float not plumbed to shader; surface.Translucency=0.5 ignored
so streaks render at 2× retail intensity).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-27 08:49:42 +02:00
parent 9567597814
commit 3e0da496e0
3 changed files with 130 additions and 5 deletions
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82
src/AcDream.App/Rendering/Sky/SkyRenderer.cs
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@ -70,8 +70,18 @@ public sealed unsafe class SkyRenderer : IDisposable
}
/// <summary>
/// Draw the sky for this frame. Called FIRST in the render loop —
/// terrain / meshes / debug lines / overlay land on top.
/// Draw all NON-WEATHER sky objects (dome, sun, moon, stars, clouds —
/// every <c>SkyObject</c> with <c>Properties &amp; 0x04 == 0</c>).
/// Called BEFORE the scene; terrain / meshes / debug lines / overlay
/// land on top via depth-test.
///
/// <para>
/// Mirrors the first half of retail's <c>LScape::draw</c> at
/// <c>0x00506330</c>: that function calls <c>GameSky::Draw(0)</c>
/// (sky pass) before the landblock loop, then <c>GameSky::Draw(1)</c>
/// (weather pass) after. acdream splits the same way — see
/// <see cref="RenderWeather"/> for the post-scene companion.
/// </para>
///
/// <para>
/// Each submesh renders with retail's per-vertex lighting formula:
@ -91,12 +101,50 @@ public sealed unsafe class SkyRenderer : IDisposable
/// field.
/// </para>
/// </summary>
public void Render(
public void RenderSky(
ICamera camera,
Vector3 cameraWorldPos,
float dayFraction,
DayGroupData? group,
SkyKeyframe keyframe)
=> RenderPass(camera, cameraWorldPos, dayFraction, group, keyframe, weatherPass: false);
/// <summary>
/// Draw the WEATHER sky objects (the foreground rain mesh
/// <c>0x01004C42</c>/<c>0x01004C44</c> on Rainy DayGroups, plus the
/// per-storm 5cm flash dummies — every <c>SkyObject</c> with
/// <c>Properties &amp; 0x04 != 0</c>). Called AFTER the scene so the
/// rain meshes paint on top of terrain and entities — that's the
/// retail-faithful order from <c>LScape::draw</c> at
/// <c>0x00506330</c>, where <c>GameSky::Draw(1)</c> fires after the
/// <c>DrawBlock</c> loop. With depth-test disabled and additive blend
/// (the rain Surface flag <c>0x080000C5</c> includes Additive), the
/// 815m-tall rain cylinder's bright streak texels add over the scene
/// — making rain appear in the air between camera and character
/// instead of only at the horizon.
/// </summary>
public void RenderWeather(
ICamera camera,
Vector3 cameraWorldPos,
float dayFraction,
DayGroupData? group,
SkyKeyframe keyframe)
=> RenderPass(camera, cameraWorldPos, dayFraction, group, keyframe, weatherPass: true);
/// <summary>
/// Shared pass for <see cref="RenderSky"/> and <see cref="RenderWeather"/>.
/// Sets up the same GL state for both (depth-test off, additive +
/// alpha-blend per submesh, camera-anchored translation) and iterates
/// only the SkyObjects matching the requested partition by
/// <see cref="SkyObjectData.IsWeather"/>.
/// </summary>
private void RenderPass(
ICamera camera,
Vector3 cameraWorldPos,
float dayFraction,
DayGroupData? group,
SkyKeyframe keyframe,
bool weatherPass)
{
if (group is null || group.SkyObjects.Count == 0) return;
@ -149,6 +197,14 @@ public sealed unsafe class SkyRenderer : IDisposable
for (int i = 0; i < group.SkyObjects.Count; i++)
{
var obj = group.SkyObjects[i];
// Partition by weather flag — the caller chose either the
// pre-scene sky pass (non-weather) or the post-scene weather
// pass (weather only). Mirrors retail GameSky::Draw at
// 0x00506ff0 where arg2==0 iterates non-weather sky_obj
// entries (filtered by property bit 0x04 == 0 inside the
// loop) and arg2==1 draws after_sky_cell which only contains
// weather objects.
if (obj.IsWeather != weatherPass) continue;
if (!obj.IsVisible(dayFraction)) continue;
// Apply per-keyframe replace overrides.
@ -177,6 +233,26 @@ public sealed unsafe class SkyRenderer : IDisposable
* Matrix4x4.CreateRotationZ(-headingRad)
* Matrix4x4.CreateRotationY(-rotationRad);
// Retail weather Z-offset (GameSky::UpdatePosition at
// 0x00506dd0, decomp lines 0x506e96..0x506e98):
//
// if (((eax_13 & 4) != 0 && (eax_13 & 8) == 0))
// int32_t var_4_1 = 0xc2f00000; // 0xc2f00000 == -120.0f
//
// Weather objects (property bit 0x04 set, bit 0x08 unset)
// have their frame origin set to player_pos + (0, 0, -120m).
// The rain cylinder GfxObjs 0x01004C42/0x01004C44 have local
// Z range 0.11..814.90 (815m tall, 113m radius). Without the
// offset the cylinder bottom sits at z=0.11 ABOVE the camera
// (skyView translation is zeroed so model-origin == camera);
// looking horizontally shows nothing, looking up shows a
// distant cylinder. With -120m the cylinder spans z =
// (camera-119.89)..(camera+694.90) in view space — camera
// is inside, looking in any direction shows surrounding
// walls — the volumetric foreground-rain look retail has.
if (weatherPass)
model = model * Matrix4x4.CreateTranslation(0f, 0f, -120f);
_shader.SetMatrix4("uModel", model);
// UV scroll accumulates real-time × velocity. Wrap to [0, 1]