feat: add per-player cosmetic state

src/main/java/de/fullrisk/citrusDev/client/cosmetic/CosmeticData.java

@@ -0,0 +1,6 @@
+package de.fullrisk.citrusDev.client.cosmetic;
+
+import net.minecraft.resources.Identifier;
+
+public record CosmeticData(Identifier id, boolean visible) {
+}

src/main/java/de/fullrisk/citrusDev/client/cosmetic/CosmeticRenderData.java

@@ -0,0 +1,6 @@
+package de.fullrisk.citrusDev.client.cosmetic;
+
+import java.util.UUID;
+
+public record CosmeticRenderData(UUID playerId, CosmeticData cosmetic, float partialTick) {
+}

src/main/java/de/fullrisk/citrusDev/client/cosmetic/CosmeticRenderStateKeys.java

@@ -0,0 +1,14 @@
+package de.fullrisk.citrusDev.client.cosmetic;
+
+import net.fabricmc.fabric.api.client.rendering.v1.RenderStateDataKey;
+import net.minecraft.client.renderer.state.level.CameraRenderState;
+
+public final class CosmeticRenderStateKeys {
+    public static final RenderStateDataKey<CosmeticRenderData> COSMETIC =
+            RenderStateDataKey.create(() -> "citrus-dev player cosmetic");
+    public static final RenderStateDataKey<CameraRenderState> CAMERA =
+            RenderStateDataKey.create(() -> "citrus-dev camera render state");
+
+    private CosmeticRenderStateKeys() {
+    }
+}

src/main/java/de/fullrisk/citrusDev/client/cosmetic/PlayerCosmetic.java

@@ -0,0 +1,24 @@
+package de.fullrisk.citrusDev.client.cosmetic;
+
+import com.geckolib.animatable.GeoAnimatable;
+import com.geckolib.animatable.instance.AnimatableInstanceCache;
+import com.geckolib.animatable.manager.AnimatableManager;
+import com.geckolib.animation.AnimationController;
+import com.geckolib.animation.RawAnimation;
+import com.geckolib.util.GeckoLibUtil;
+
+public final class PlayerCosmetic implements GeoAnimatable {
+    private static final RawAnimation IDLE = RawAnimation.begin().thenLoop("animation.backpack.idle");
+
+    private final AnimatableInstanceCache cache = GeckoLibUtil.createInstanceCache(this, false);
+
+    @Override
+    public void registerControllers(AnimatableManager.ControllerRegistrar controllers) {
+        controllers.add(new AnimationController<PlayerCosmetic>(state -> state.setAndContinue(IDLE)));
+    }
+
+    @Override
+    public AnimatableInstanceCache getAnimatableInstanceCache() {
+        return cache;
+    }
+}

src/main/java/de/fullrisk/citrusDev/client/cosmetic/PlayerCosmeticManager.java

@@ -0,0 +1,43 @@
+package de.fullrisk.citrusDev.client.cosmetic;
+
+import net.minecraft.resources.Identifier;
+
+import java.util.Optional;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class PlayerCosmeticManager {
+    private static final ConcurrentHashMap<UUID, CosmeticData> COSMETICS = new ConcurrentHashMap<>();
+    private static final ConcurrentHashMap<UUID, PlayerCosmetic> ANIMATABLES = new ConcurrentHashMap<>();
+    private static final CosmeticData TEST_BACKPACK = new CosmeticData(
+            Identifier.fromNamespaceAndPath("citrus-dev", "backpack"), true);
+
+    private PlayerCosmeticManager() {
+    }
+
+    public static Optional<CosmeticData> getCosmetic(UUID playerId) {
+        return Optional.ofNullable(COSMETICS.get(playerId));
+    }
+
+    public static void setCosmetic(UUID playerId, CosmeticData cosmetic) {
+        COSMETICS.put(playerId, cosmetic);
+    }
+
+    public static void removeCosmetic(UUID playerId) {
+        COSMETICS.remove(playerId);
+        ANIMATABLES.remove(playerId);
+    }
+
+    public static PlayerCosmetic getOrCreateAnimatable(UUID playerId) {
+        return ANIMATABLES.computeIfAbsent(playerId, ignored -> new PlayerCosmetic());
+    }
+
+    public static void clear() {
+        COSMETICS.clear();
+        ANIMATABLES.clear();
+    }
+
+    public static void enableTestCosmetic(UUID playerId) {
+        setCosmetic(playerId, TEST_BACKPACK);
+    }
+}