feat(world): add CelestialSystem/BackdropProvider#getMoonPhase() - #5387
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feat(world): add CelestialSystem/BackdropProvider#getMoonPhase()#5387soloturn wants to merge 2 commits into
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#94: a hook for basing the moon's phase on the game's day counter, without requiring any new art or a persisted "date" concept - the issue's own author only asked for "some sort of hook into basing the phase on a date/counter/something". WorldTime.getDays() already provides a continuous day counter (used by DefaultCelestialSystem.getSunPosAngle() for the sun's position). getMoonPhase() derives from the same counter: (days % MOON_CYCLE_DAYS) / MOON_CYCLE_DAYS, a value in [0, 1) where 0 is new moon and 0.5 is full moon. MOON_CYCLE_DAYS defaults to the real-world synodic month (29.53 days) so a calendar or astronomy system built on top of this later lines up with familiar phase names/timing, matching the issue's own framing ("this could come later and be the basis for an astronomical system"). Added to CelestialSystem (implemented by DefaultCelestialSystem) and BackdropProvider (implemented by Skysphere, which already delegates getSunPositionAngle() etc. to CelestialSystem the same way) - both interfaces have exactly one implementation each, so this is a contained addition. A companion PR in Terasology/CoreRendering (MovingBlocks/Terasology depends on it for the actual sky rendering) uses this to make the existing "moon" highlight glow in the skysphere shader dim toward new moon and brighten toward full moon, rather than staying at constant intensity - a real, visible use of the hook using existing rendering infrastructure, no new textures/art required. ## Verification :engine:compileJava and :engine-tests:compileTestJava both clean. Added DefaultCelestialSystemTest covering the new logic directly (day 0 = new moon, half a cycle = full moon, wraps correctly after one cycle and after many cycles, stays in range while the sun is halted) - unlike most of this session's rendering-adjacent fixes, this part is pure logic with no GL dependency, so it's genuinely unit-tested: 5/5 pass. Also ran the full integrationenvironment suite (18 MTE test classes, 34 tests) to confirm the BackdropProvider/ CelestialSystem interface changes don't break world bootstrap, which depends on both - all pass. Fixes #94 Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Included review availability: Your plan provides up to 8 included reviews per hour; 6 remain after this review. 📝 WalkthroughSummary by CodeRabbit
WalkthroughThe celestial system calculates a normalized moon phase over a 29.53-day cycle. The phase is exposed through ChangesMoon phase support
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to This adds a day-counter-based moon-phase hook through the existing celestial and backdrop APIs, with focused tests and integration verification; no actionable merge-blocking risk remains beyond normal checks and review. Sequence Diagram(s)sequenceDiagram
participant Skysphere
participant CelestialSystem
participant DefaultCelestialSystem
participant WorldTime
Skysphere->>CelestialSystem: getMoonPhase()
CelestialSystem->>DefaultCelestialSystem: calculate normalized phase
DefaultCelestialSystem->>WorldTime: read current or halted days
WorldTime-->>DefaultCelestialSystem: day value
DefaultCelestialSystem-->>Skysphere: phase in [0, 1)
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Inline comments:
In
`@engine/src/main/java/org/terasology/engine/world/sun/DefaultCelestialSystem.java`:
- Around line 36-40: Move the static constant MOON_CYCLE_DAYS above all instance
fields in DefaultCelestialSystem, preserving its value and documentation while
satisfying DeclarationOrderCheck.
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engine-tests/src/test/java/org/terasology/engine/world/sun/DefaultCelestialSystemTest.javaengine/src/main/java/org/terasology/engine/rendering/backdrop/BackdropProvider.javaengine/src/main/java/org/terasology/engine/rendering/backdrop/Skysphere.javaengine/src/main/java/org/terasology/engine/world/sun/CelestialSystem.javaengine/src/main/java/org/terasology/engine/world/sun/DefaultCelestialSystem.java
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This was referenced Aug 20, 2026
DeclarationOrder: the static final field was declared after the instance fields it precedes conceptually; checkstyle wants class (static) variables before instance variables. No behavior change. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Fixes #94 - a hook for basing the moon's phase on the game's day counter, without requiring any new art or a persisted "date" concept. The issue's own author only asked for "some sort of hook into basing the phase on a date/counter/something".
What changed
WorldTime.getDays()already provides a continuous day counter (used byDefaultCelestialSystem.getSunPosAngle()for the sun's position).getMoonPhase()derives from the same counter:(days % MOON_CYCLE_DAYS) / MOON_CYCLE_DAYS, a value in[0, 1)where0is new moon and0.5is full moon.MOON_CYCLE_DAYSdefaults to the real-world synodic month (29.53 days) so a calendar or astronomy system built on top of this later lines up with familiar phase names/timing, matching the issue's own framing ("this could come later and be the basis for an astronomical system").Added to
CelestialSystem(implemented byDefaultCelestialSystem) andBackdropProvider(implemented bySkysphere, which already delegatesgetSunPositionAngle()etc. toCelestialSystemthe same way) - both interfaces have exactly one implementation each, so this is a contained addition.A companion PR in Terasology/CoreRendering (#86) uses this to make the existing "moon" highlight glow in the skysphere shader dim toward new moon and brighten toward full moon, rather than staying at constant intensity - a real, visible use of the hook using existing rendering infrastructure, no new textures/art required.
Note on scope
This issue carries
Type: DreamandRevive: Convertlabels - the maintainers' own triage said it should become a GitHub Discussion rather than stay an actionable issue. It was implemented here on the requester's explicit instruction despite that. Please weigh that context when reviewing/merging.Verification
:engine:compileJavaand:engine-tests:compileTestJavaboth clean. AddedDefaultCelestialSystemTestcovering the new logic directly (day 0 = new moon, half a cycle = full moon, wraps correctly after one cycle and after many cycles, stays in range while the sun is halted) - unlike most rendering-adjacent code, this part is pure logic with no GL dependency, so it's genuinely unit-tested: 5/5 pass. Also ran the fullintegrationenvironmentsuite (18 MTE test classes, 34 tests) to confirm theBackdropProvider/CelestialSysteminterface changes don't break world bootstrap, which depends on both - all 34 pass.The rendering side (CoreRendering PR) still needs a live playtest to confirm the visual fade reads correctly - noted there.