Pine trees in direct sunlight (noon) looked like sheets with no volume, with dappled shadows completely missing under the trees and a bright, flat ground. Shadowed areas were normal — a typical symptom of directional light castDynamicShadows=false, which Lumen indirect lighting cannot make up for.
— On-site symptom description
1. Root-Cause Diagnosis (Three Rounds of Elimination)
Round 1: misdiagnosed Lumen off → eliminated
At first glance, Config/DefaultEngine.ini had r.DynamicGlobalIlluminationMethod=0 and r.ReflectionMethod=0 (= None). Restoring to 1 (Lumen) and restarting PIE produced no change.
Conclusion: Lumen only controls the softness of indirect lighting; the presence/absence of dynamic shadows is not its job — it belongs to the castDynamicShadows switch on the directional light component.
Round 2: read runtime CVar → confirmed GI is on
Read the runtime-effective values using Unreal Editor MCP 8017's EditorToolset.EditorAppToolset.SearchCVars:
| CVar | Actual value | Conclusion |
|---|---|---|
| r.DynamicGlobalIlluminationMethod | 1 (Lumen) | Lumen GI on ✅ |
| r.Lumen.DiffuseIndirect.Allow | 1 | Lumen indirect lighting allowed ✅ |
| r.ContactShadows | 1 | Contact shadows on ✅ |
| r.Nanite | 1 | Nanite on ✅ |
| r.Shadow.Virtual.Enable | 1 | Virtual shadow maps (VSM) on ✅ |
Round 3: direct to light component properties → root cause locked
Sun/Moon is managed by the level SunMoonDaySequenceActor_0; component path:
/Game/_LevelSeting/MMOGameMap_01.MMOGameMap_01:PersistentLevel.SunMoonDaySequenceActor_0.Sun
Read the Sun/Moon key attributes with ObjectTools.get_properties:
| Property | Sun value | Moon value | Judgment |
|---|---|---|---|
| castShadows | true | true | Master switch on ✅ |
| castStaticShadows | true | true | Static shadows on ✅ |
| castDynamicShadows | false | false | ⚠️ Root cause! |
| intensity | 18900 | 60 | Normal |
| castRaytracedShadow | UseProjectSetting | — | Follows project setting |
2. Why castDynamicShadows=false Causes Paper-Thin Foliage
- Pine trees are dynamic Foliage instances, not static meshes; the sun is a Movable directional light (DaySequence must rotate to follow time).
- Dynamic shadows on a Movable directional light rely entirely on castDynamicShadows. false → dynamic foliage casts no shadows at all.
- Only Static ground can receive static shadows → the ground is bright but tree shadows are nowhere; visually flat.
- VSM happens to be on, so dynamic shadows depend even more on castDynamicShadows.
3. The Fix (One MCP set + read-back + save)
# Unreal Editor MCP 8017 · Python 调用序列
# 1. set Sun.castDynamicShadows = true
ObjectTools.set_properties(
instance="/Game/_LevelSeting/MMOGameMap_01..."
":PersistentLevel.SunMoonDaySequenceActor_0.Sun",
values={"castDynamicShadows": True})
# 2. set Moon.castDynamicShadows = true（同理）
# 3. 回读验证（必须，set 可能静默失败）
ObjectTools.get_properties(
instance=Sun,
properties=["castDynamicShadows","castStaticShadows"])
# → castDynamicShadows=True ✅
# 4. 保存关卡
AssetTools.save_assets(asset_paths=["/Game/_LevelSeting/MMOGameMap_01"])No editor restart, straight into PIE at noon → foliage restored: dappled shadows appear under the trees and foliage regains its sense of volume.
4. How to Quickly Diagnose Similar Problems in the Future (Diagnostic Path)
# 全在 Unreal Editor MCP 8017 上
1. SceneTools.find_actors(name="SunMoonDaySequence") → 找 Actor refPath
2. ActorTools.get_components(actor) → 列出 Sun / Moon 组件路径
3. ObjectTools.get_properties(instance=Sun,
properties=["castShadows","castStaticShadows","castDynamicShadows","intensity"])
4. castDynamicShadows=false → set true → 回读 → save_assets 关卡5. Possible Recurrence Points
This fix changed the level instance property. If dynamic shadows vanish again after restarting the editor/PIE → the Sun/Moon components are default child objects of the DaySequence plugin class and their template values are still false; the same setting must also be applied on the plugin class CDO (the component's _GEN_VARIABLE template) for a permanent fix.