From d6535dc9cd6deb9e20d67ddd0270f2e43f506172 Mon Sep 17 00:00:00 2001
From: Jozufozu <jozsefaug@gmail.com>
Date: Sun, 21 May 2023 16:07:46 -0700
Subject: [PATCH] Gone, but not forgotten

- Track the last visible AABB within EntityVisuals to prevent entities
  from freezing when the go offscreen.
---
 .../lib/visual/AbstractEntityVisual.java      | 11 ++--
 .../lib/visual/EntityVisibilityTester.java    | 53 +++++++++++++++++++
 2 files changed, 56 insertions(+), 8 deletions(-)
 create mode 100644 src/main/java/com/jozufozu/flywheel/lib/visual/EntityVisibilityTester.java

diff --git a/src/main/java/com/jozufozu/flywheel/lib/visual/AbstractEntityVisual.java b/src/main/java/com/jozufozu/flywheel/lib/visual/AbstractEntityVisual.java
index 880550a75..4647bf889 100644
--- a/src/main/java/com/jozufozu/flywheel/lib/visual/AbstractEntityVisual.java
+++ b/src/main/java/com/jozufozu/flywheel/lib/visual/AbstractEntityVisual.java
@@ -35,11 +35,13 @@ import net.minecraft.world.phys.Vec3;
 public abstract class AbstractEntityVisual<T extends Entity> extends AbstractVisual implements EntityVisual<T>, TickingLightListener {
 	protected final T entity;
 	protected final MutableBox bounds;
+	protected final EntityVisibilityTester boxTracker;
 
 	public AbstractEntityVisual(VisualizationContext ctx, T entity) {
 		super(ctx, entity.level);
 		this.entity = entity;
 		bounds = MutableBox.from(entity.getBoundingBox());
+		boxTracker = new EntityVisibilityTester(entity, ctx.renderOrigin());
 	}
 
 	@Override
@@ -99,13 +101,6 @@ public abstract class AbstractEntityVisual<T extends Entity> extends AbstractVis
 		if (entity.noCulling) {
 			return true;
 		}
-
-		AABB aabb = entity.getBoundingBoxForCulling();
-		return frustum.testAab((float) (aabb.minX - renderOrigin.getX()) - 0.5f,
-				(float) (aabb.minY - renderOrigin.getY()) - 0.5f,
-				(float) (aabb.minZ - renderOrigin.getZ()) - 0.5f,
-				(float) (aabb.maxX - renderOrigin.getX()) + 0.5f,
-				(float) (aabb.maxY - renderOrigin.getY()) + 0.5f,
-				(float) (aabb.maxZ - renderOrigin.getZ()) + 0.5f);
+		return boxTracker.isVisible(frustum);
 	}
 }
diff --git a/src/main/java/com/jozufozu/flywheel/lib/visual/EntityVisibilityTester.java b/src/main/java/com/jozufozu/flywheel/lib/visual/EntityVisibilityTester.java
new file mode 100644
index 000000000..649e4edae
--- /dev/null
+++ b/src/main/java/com/jozufozu/flywheel/lib/visual/EntityVisibilityTester.java
@@ -0,0 +1,53 @@
+package com.jozufozu.flywheel.lib.visual;
+
+import org.jetbrains.annotations.Nullable;
+import org.joml.FrustumIntersection;
+
+import net.minecraft.core.Vec3i;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.phys.AABB;
+
+/**
+ * A helper class for testing whether an Entity is visible.
+ * <p>
+ * The last visible AABB is also checked to prevent the Entity from freezing when it goes offscreen.
+ */
+public class EntityVisibilityTester {
+	private final Entity entity;
+	private final Vec3i renderOrigin;
+	@Nullable
+	private AABB lastVisibleAABB;
+
+	public EntityVisibilityTester(Entity entity, Vec3i renderOrigin) {
+		this.entity = entity;
+
+		this.renderOrigin = renderOrigin;
+	}
+
+	public boolean isVisible(FrustumIntersection frustum) {
+		AABB aabb = entity.getBoundingBoxForCulling();
+
+		boolean visible = adjustAndTestAABB(frustum, aabb);
+
+		if (!visible && lastVisibleAABB != null && lastVisibleAABB != aabb) {
+			// If the entity isn't visible, check the last visible AABB as well.
+			// This is to avoid Entities freezing when the go offscreen.
+			visible = adjustAndTestAABB(frustum, lastVisibleAABB);
+		}
+
+		if (visible) {
+			lastVisibleAABB = aabb;
+		}
+		return visible;
+	}
+
+	private boolean adjustAndTestAABB(FrustumIntersection frustum, AABB aabb) {
+		float minX = (float) (aabb.minX - renderOrigin.getX() - 0.5);
+		float minY = (float) (aabb.minY - renderOrigin.getY() - 0.5);
+		float minZ = (float) (aabb.minZ - renderOrigin.getZ() - 0.5);
+		float maxX = (float) (aabb.maxX - renderOrigin.getX() + 0.5);
+		float maxY = (float) (aabb.maxY - renderOrigin.getY() + 0.5);
+		float maxZ = (float) (aabb.maxZ - renderOrigin.getZ() + 0.5);
+		return frustum.testAab(minX, minY, minZ, maxX, maxY, maxZ);
+	}
+}