APLM Controller

BP_APLMController is the Blueprint that brings APLM to life at runtime. It is the bridge between your project (your sky system, your save game, your in-world calendar) and the two Material Parameter Collections that the material reads every frame: MPC_Seasons and MPC_Weathers.

You drop it in your level once. You assign one data asset per biome. From that point on it handles the rest: pushing seasonal color shifts into the material, exposing weather entry points that you can call when it rains or snows, and managing the transitions in between.

If you have ever wondered how a tropical rainforest can stay green in summer and turn rich after rain while the neighbouring desert keeps its sun-baked look, this is the actor doing the orchestration.

What it controls

• Seasons, by writing the per-biome color, brightness, contrast, specular, and roughness values into MPC_Seasons every tick.
• Weather, by exposing one rain entry point and one snow entry point per layer (each biome and most base layers). Calling these from your weather system pushes the right intensity values into MPC_Weathers.
• Smooth transitions between consecutive seasons through an internal lerp helper, so a forest does not snap from summer to autumn.

How you use it

1. Drag BP_APLMController into your level. One instance per level is enough.
2. In the Details panel, assign one data asset per biome:
   • BP_TundraData, BP_BorealData, BP_DesertData, BP_MediterraneanData, BP_SavannaData, BP_TemperateForestData, BP_TropicalRainforestData, BP_WetlandData, BP_GrasslandData, BP_Custom1Data, BP_Custom2Data, BP_Custom3Data.
   • Each data asset holds the per-season values (color, color grade, specular, roughness) for that biome.
3. From your gameplay or sky/weather system, call the per-layer weather entry points when conditions change. For example, when rain starts in the forest region, call TemperateForestWeatherRain. When it stops, call it again with the value you want to ease back to.
4. The controller’s tick logic does the rest: it picks the current and next season, runs the lerp, and writes the resulting values into MPC_Seasons.

Tip

You do not have to use it. The controller is the convenience path. If you want to write into MPC_Seasons and MPC_Weathers from your own actor, Sequencer, or game-mode logic, that works too. APLM only cares about what ends up in the MPCs, not who put it there.

Public functions

The controller exposes a small set of functions you might call from your own Blueprints. Most users only ever call the per-layer weather ones; the rest run on tick automatically.

Per-layer weather

For every biome layer (Tundra, BorealForest, Desert, Mediterranean, Savanna, TemperateForest, TropicalRainForest, Wetland, Grassland, Custom1, Custom2, Custom3) and most base layers (Beach, Cliff, Grass, Gravel):

• [Layer]WeatherRain — set the rain intensity for that layer.
• [Layer]WeatherSnow — set the snow intensity for that layer.

Cliff has only the rain variant, which matches how cliffs respond in the material.

Season pipeline (runs automatically)

Function	What it does
AllVariables	Calls every per-biome push function in turn. Runs once per tick.
AllNodes	Wider master that bundles related setup steps.
PerBiomeSorting	Keeps each biome’s per-season list in the right order before reading.
SetSeasonIndex	Updates which season is currently active.
GetCurrentSeasonData	Returns the data for the active season.
GetNextSeasonData	Returns the data for the season we are blending toward.
SeasonLerp	Interpolates between current and next season values. The result drives the MPC writes.
SeasonTransition	Owns the transition lifecycle (when to advance, how long to blend).
[Biome]Variables	One push function per biome (e.g. TundraVariables, BorealForestVariables). Reads the lerp result and writes that biome’s parameters into MPC_Seasons.

You normally do not call these. They run on tick. They are documented here so you know what is happening when you inspect the Blueprint.

Variables on the controller

Variable	Type	What it holds
BP_TundraData	BP_Season	Per-season values for the Tundra biome.
BP_BorealData	BP_Season	Per-season values for Boreal Forest.
BP_DesertData	BP_Season	Per-season values for Desert.
BP_MediterraneanData	BP_Season	Per-season values for Mediterranean.
BP_SavannaData	BP_Season	Per-season values for Savanna.
BP_TemperateForestData	BP_Season	Per-season values for Temperate Forest.
BP_TropicalRainforestData	BP_Season	Per-season values for Tropical Rainforest.
BP_WetlandData	BP_Season	Per-season values for Wetland.
BP_GrasslandData	BP_Season	Per-season values for Grassland.
BP_Custom1Data	BP_Season	Per-season values for Custom 1.
BP_Custom2Data	BP_Season	Per-season values for Custom 2.
BP_Custom3Data	BP_Season	Per-season values for Custom 3.

Each BP_Season data asset stores an ordered list of F_SeasonParameters entries, one per season. The order in the asset is the order the controller cycles through them.

Structs it uses

Struct	What it holds
F_ColorGrade	Offset, gain, brightness, contrast, saturation.
F_SeasonCore	The eight seasonal values per biome (color, color grade, specular, roughness).
F_SeasonMetadata	Identity and labelling fields for one season entry (display name, index, and so on).
F_SeasonParameters	One full season entry: metadata plus the core values.
F_WeatherParameters	The weather payload (rain and snow intensities) the controller writes into MPC_Weathers.

You can use these structs as is, or extend them in your own Blueprints. Many projects only need the shipped structs.

Where to next

• Driving seasons from Blueprint: the four-step setup that uses this controller end to end
• Season system concept: the design rationale for the season pipeline
• Weather system concept: how MPC_Weathers drives per-material rain and snow
• Season parameters reference: the eight per-biome seasonal overrides this controller writes
• Weather parameters reference: the per-layer weather controls this controller drives