Screen-Space GPU Rain – Shogun Exodus Devlog #37

Raw Patch Notes

UPDATE 2026-08-23 #192 - Rain GPU Weather Effect
- Added one reusable `rain_sheet` Weather Effect: a single additive, untextured GPUParticles2D reproducing the selected tutorial setup at exactly 1000 particles, including box emission, 3000px/s² gravity, velocity-aligned Y streak scaling, initial-alpha ramp, lifetime alpha curve, one-second lifetime, and 0.5-second preprocess. No custom texture/shader, trails, turbulence, collision, subemitters, controller, timer, or per-particle CPU work was added.
- Rain is screen-space and screen-budgeted. The emitter follows the rendered camera center with inverse zoom and local particle coordinates, derives emission/culling geometry from the viewport only when camera/zoom/viewport changes, and never increases amount for the larger world area visible at extreme zoom. GPUParticles2D.speed_scale follows TimeSystem's soft pause and x1/x2/x4 signals; opacity fades fulfill the existing binder lifecycle and report renderer CPU work under `weather_fx`.
- Registered `rain_sheet` in its own mod-mergeable `rain_effects.json` on the `foreground` host. All three Rain states are available to automatic planning and the existing Dev Tools Spawn/Force paths, and the generic effect test scene defaults to Rain on `foreground`.
- Corrected stale darkness documentation: `behind_mountains` is darkened directly by WorldTerrainBackground; only `overall_background` remains non-darkened. Added current Rain architecture/modding documentation and one player-facing Rain loading hint.
- Tuned the visually approved normal Rain technique without changing its speed or architecture: density increased 50% from 1000 to 1500 particles, the lifetime alpha plateau increased 25% from 0.30 to 0.375, and a constant 1.1x X curve now makes the untextured drops slightly thicker without altering their existing Y-stretch curve.
- Gravity, lifetime, preprocess, fall speed, camera behavior, screen-based budget, host, fade lifecycle, and TimeSystem integration remain unchanged. The previous 1000-particle, 0.30-alpha, un-widened setup became the starting reference for Light Rain.
- Added `light_rain` and `heavy_rain` as data presets of the existing single `rain_sheet` scene/effect, not separate renderers or systems. Light uses density 700, lifetime-alpha plateau 0.25, and the original 1.0x drop width; Heavy uses density 2500, alpha 0.4, and 1.375x width (25% thicker than normal Rain's current 1.1x). Normal remains 1500/0.375/1.1x.
- RainSheet now consumes max-oriented `alpha_strength` and `drop_width_multiplier` parameters alongside density/overall opacity. Only the mutable X-width and alpha curves are duplicated per runtime instance; the Y-stretch and other authored particle resources stay shared. All three presets retain identical gravity, lifetime, preprocess, speed, additive blend, camera behavior, time scaling, and one-layer GPU architecture.
- Enabled the existing Light Rain and Heavy Rain precipitation states and attached their matching presets. The existing data-driven Dev Tools Weather menu now exposes None, Light Rain, Rain, and Heavy Rain automatically; no Rain-specific menu/controller code was added.
- Connected the existing `rain_sheet` effect to `wind/speed_kmh` through the generic registry `weather_inputs` contract. RainSheet receives only plain cached response endpoints/timestamps and interpolates them in game time; it never queries WeatherSystem. The shared max-oriented `horizontal_push_at_reference` passthrough defaults to 300, producing `gravity.x = -300 * wind_response` while preserving vertical gravity 3000. Existing Align Y to Velocity rotates all three Rain presets with their diagonal motion.
- Added event-derived right-side emission overscan equal to the greatest current/target horizontal displacement over the one-second particle lifetime. Overscan recalculates on Wind descriptor, reference-push, or camera/viewport changes and expands culling bounds accordingly. Light/normal/Heavy remain fixed at 700/1500/2500 particles, so strong Wind never raises GPU allocation to compensate for the wider emitter.
- Wind transitions reuse RainSheet's existing renderer process and TimeSystem game-hour clock, freezing on soft pause and scaling with game speed. Gravity is written only when the interpolated response changes; stable Wind adds no material churn. No Rain controller, timer, tick, turbulence, random direction, density/alpha/width coupling, or per-particle CPU logic was added. Updated the player Wind loading hint to include Rain.
- Standardized Light/normal/Heavy Rain destination fades at 0.5 game hours, making every Rain-to-Rain intensity change take 30 in-game minutes instead of visually snapping even though the same effect instance remained active. RainSheet now fades density, lifetime-alpha strength, and X width together through the existing destination fade spec; it still has no state identity or hardcoded transition duration.
- Density uses `GPUParticles2D.amount_ratio` only as a transition bridge. Growing Rain allocates the destination amount once and begins at the equivalent current ratio; weakening Rain lowers the ratio against the current allocation, then commits the true smaller `amount` at fade completion. Light Rain therefore returns to a stable 700-particle allocation rather than retaining Heavy Rain's 2500-particle cost. The existing 0.5-second preprocess covers the infrequent amount restart boundary.
- Fresh None->Rain instances snap their preset look while fully transparent and keep the established opacity fade. Blank-fade Force/load paths snap and commit immediately. Alpha/width curve and amount-ratio writes are gated to actual look transitions, so opacity-only appearance/removal fades add no unnecessary resource churn. Game-hour transitions freeze on soft pause and scale with x1/x2/x4.
- Rebalanced the precipitation planner's initial Alpha-stage cadence. Effective Wet/Normal/Dry weights are now None 0.70/1.50/3.60, Light Rain 1.40/0.75/0.55, Rain 2.40/0.65/0.20, and Heavy Rain 1.50/0.30/0.08; their uniformly rolled minimum dwells are respectively 6-16, 4-12, 4-14, and 3-11 game hours. These effective values are encoded through each state's base weight and rainfall-characteristic multiplier, preserving the generic mod-facing weight contract.
- Clarified the Rain tuning contract beside the data and Inspector exports: density controls drop count, alpha strength controls lifetime visibility, width changes X thickness only, opacity fades the entire sheet, and reference Wind push controls diagonal slant. The Weather architecture and mod guide now also distinguish effective precipitation weights from their stored base/multiplier representation and minimum dwell from actual joint-cluster hold time.
- Files: `Scenes/Enviroment/Weather_Systems/RainSheet.tscn`, `Scripts/Weather_Systems/RainSheet.gd`, `Scripts/Weather_Systems/WeatherEffectBase.gd`, `Data/Weather_Systems/Effects/rain_effects.json`, `Data/Weather_Systems/conditions.json`, `Data/LoadingScreenText.json`, `Scenes/TestScenesDev/WeatherEffectTestScene.tscn`, `DeveloperFiles/Weather_System_Explainer.txt`, `DeveloperFiles/World_Background_Explainer.txt`, `DeveloperFiles/current-game-setup.txt`, `DeveloperFiles/mod-guide.txt`, `DeveloperFiles/briefs/rain-effect-baseline-brief.md`, `DeveloperFiles/update-log.txt`.
- Updates 187-191 were consolidated into update 192.

*This is an automated post, using Python and LLMs to summarize game updates. Mistakes, while rare, may happen.