And I oobe

- Raise exception when trying to slice outside DrawBuffer bounds
- Count vertices in BufferPlan#execute to account for instance creation
  during Visual updates
- Mark DrawBuffers active by default

src/main/java/com/jozufozu/flywheel/backend/engine/batching/BatchingDrawTracker.java

@@ -40,6 +40,13 @@ public class BatchingDrawTracker {
 		}
 	}
 
+	public void markInactive(RenderStage stage, DrawBuffer buffer) {
+		synchronized (activeBuffers) {
+			activeBuffers.get(stage)
+					.remove(buffer);
+		}
+	}
+
 	/**
 	 * Draw and reset all DrawBuffers for the given RenderStage.
 	 *
@@ -75,7 +82,9 @@ public class BatchingDrawTracker {
 	}
 
 	public boolean hasStage(RenderStage stage) {
-		return !activeBuffers.get(stage)
-				.isEmpty();
+		synchronized (activeBuffers) {
+			return !activeBuffers.get(stage)
+					.isEmpty();
+		}
 	}
 }

src/main/java/com/jozufozu/flywheel/backend/engine/batching/BatchingEngine.java

@@ -51,15 +51,10 @@ public class BatchingEngine extends AbstractEngine {
 		var stack = FlwUtil.copyPoseStack(context.stack());
 		stack.translate(renderOrigin.getX() - cameraPos.x, renderOrigin.getY() - cameraPos.y, renderOrigin.getZ() - cameraPos.z);
 
-		double cameraX = cameraPos.x;
-		double cameraY = cameraPos.y;
-		double cameraZ = cameraPos.z;
-
 		org.joml.Matrix4f proj = MatrixUtil.toJoml(context.viewProjection());
-		proj.translate((float) (renderOrigin.getX() - cameraX), (float) (renderOrigin.getY() - cameraY), (float) (renderOrigin.getZ() - cameraZ));
-		FrustumIntersection frustum = new FrustumIntersection(proj);
+		proj.translate((float) (renderOrigin.getX() - cameraPos.x), (float) (renderOrigin.getY() - cameraPos.y), (float) (renderOrigin.getZ() - cameraPos.z));
 
-		var ctx = new FrameContext(context.level(), stack.last(), frustum);
+		var ctx = new FrameContext(context.level(), stack.last(), new FrustumIntersection(proj));
 
 		flush();
 

src/main/java/com/jozufozu/flywheel/backend/engine/batching/BatchingStage.java

@@ -11,7 +11,6 @@ import com.jozufozu.flywheel.api.task.Plan;
 import com.jozufozu.flywheel.api.task.TaskExecutor;
 import com.jozufozu.flywheel.lib.task.NestedPlan;
 import com.jozufozu.flywheel.lib.task.Synchronizer;
-import com.jozufozu.flywheel.lib.task.UnitPlan;
 
 import net.minecraft.client.renderer.RenderType;
 
@@ -51,7 +50,6 @@ public class BatchingStage {
 		private final DrawBuffer buffer;
 		private final List<TransformCall<?>> transformCalls = new ArrayList<>();
 		private FrameContext ctx;
-		private int vertexCount;
 
 		public BufferPlan(DrawBuffer drawBuffer) {
 			buffer = drawBuffer;
@@ -60,14 +58,7 @@ public class BatchingStage {
 		public Plan update(FrameContext ctx) {
 			this.ctx = ctx;
 
-			vertexCount = setupAndCountVertices();
-			if (vertexCount <= 0) {
-				return UnitPlan.INSTANCE;
-			}
-
-			// Moving this into execute leads to a race condition that causes things to flash in and out of existence.
-			// Sometimes the main thread decides there's nothing to render in a stage before the worker threads have
-			// marked a stage as active. Then in the next frame #markActive complains because it's already prepared.
+			// Mark the tracker active by default...
 			tracker.markActive(stage, buffer);
 			return this;
 		}
@@ -78,7 +69,18 @@ public class BatchingStage {
 
 		@Override
 		public void execute(TaskExecutor taskExecutor, Runnable onCompletion) {
+			// Count vertices here to account for instances being added during Visual updates.
+			var vertexCount = setupAndCountVertices();
+
+			if (vertexCount <= 0) {
+				// ...then mark it inactive if there's nothing to draw.
+				tracker.markInactive(stage, buffer);
+				onCompletion.run();
+				return;
+			}
+
 			AtomicInteger vertexCounter = new AtomicInteger(0);
+
 			buffer.prepare(vertexCount);
 
 			var synchronizer = new Synchronizer(transformCalls.size(), () -> {

src/main/java/com/jozufozu/flywheel/backend/engine/batching/TransformCall.java

@@ -65,6 +65,10 @@ public class TransformCall<I extends Instance> {
 
 			final int baseVertex = vertexCount.getAndAdd(meshVertexCount);
 
+			if (baseVertex + meshVertexCount > buffer.getVertexCount()) {
+				throw new IndexOutOfBoundsException("Vertex count greater than allocated: " + baseVertex + " + " + meshVertexCount + " > " + buffer.getVertexCount());
+			}
+
 			var sub = buffer.slice(baseVertex, meshVertexCount);
 
 			mesh.copyTo(sub.ptr());