feat: Highlight century cake slice players

src/main/kotlin/events/EntityRenderTintEvent.kt

@@ -0,0 +1,66 @@
+package moe.nea.firmament.events
+
+import net.minecraft.client.render.GameRenderer
+import net.minecraft.client.render.OverlayTexture
+import net.minecraft.client.render.entity.state.EntityRenderState
+import net.minecraft.entity.Entity
+import net.minecraft.entity.LivingEntity
+import moe.nea.firmament.util.render.TintedOverlayTexture
+
+/**
+ * Change the tint color of a [LivingEntity]
+ */
+class EntityRenderTintEvent(
+	val entity: Entity,
+	val renderState: HasTintRenderState
+) : FirmamentEvent.Cancellable() {
+	init {
+		if (entity !is LivingEntity) {
+			cancel()
+		}
+	}
+
+	companion object : FirmamentEventBus<EntityRenderTintEvent>() {
+		/**
+		 * Static variable containing an override for [GameRenderer.getOverlayTexture]. Should be only set briefly.
+		 *
+		 * This variable only affects render layers that naturally make use of the overlay texture, have proper overlay UVs set (`overlay u != 0`), and have a shader that makes use of the overlay (does not have the `NO_OVERLAY` flag set in its json definition).
+		 *
+		 * Currently supported layers: [net.minecraft.client.render.entity.equipment.EquipmentRenderer], [net.minecraft.client.render.entity.model.PlayerEntityModel], as well as some others naturally.
+		 *
+		 * @see moe.nea.firmament.mixins.render.entitytints.ReplaceOverlayTexture
+		 * @see TintedOverlayTexture
+		 */
+		@JvmField
+		var overlayOverride: OverlayTexture? = null
+	}
+
+	@Suppress("PropertyName", "FunctionName")
+	interface HasTintRenderState {
+		/**
+		 * Multiplicative tint applied before the overlay.
+		 */
+		var tint_firmament: Int
+
+		/**
+		 * Must be set for [tint_firmament] to have any effect.
+		 */
+		var hasTintOverride_firmament: Boolean
+
+		// TODO: allow for more specific selection of which layers get tinted
+		/**
+		 * Specify a [TintedOverlayTexture] to be used. This does not apply to render layers not using the overlay texture.
+		 * @see overlayOverride
+		 */
+		var overlayTexture_firmament: TintedOverlayTexture?
+		fun reset_firmament()
+
+		companion object {
+			@JvmStatic
+			fun cast(state: EntityRenderState): HasTintRenderState {
+				return state as HasTintRenderState
+			}
+		}
+	}
+
+}