To delete or not to delete

- Fix AtomicBitset#nextClearBit
- Add test for AtomicBitset
- Remove unnecessary gl state stuff from IndirectEngine#renderCrumbling.
- Fix instance removal on IndirectEngine.
  - Deleting an instance not at the end of the instancers list would
    cause an exception to be thrown during upload caused by
    out-of-bounds indexing.
  - Fixed by unsetting changed for the tail of the instancers list.

src/main/java/com/jozufozu/flywheel/backend/engine/AbstractInstancer.java

@@ -40,11 +40,6 @@ public abstract class AbstractInstancer<I extends Instance> implements Instancer
 		return instances.size();
 	}
 
-	protected boolean moreThanTwoThirdsChanged() {
-		return (changed.cardinality() * 3) > (instances.size() * 2);
-	}
-
-
 	public void notifyDirty(int index) {
 		if (index < 0 || index >= getInstanceCount()) {
 			return;
@@ -68,21 +63,34 @@ public abstract class AbstractInstancer<I extends Instance> implements Instancer
 		final int oldSize = this.instances.size();
 		int removeCount = deleted.cardinality();
 
+		if (oldSize == removeCount) {
+			clear();
+			return;
+		}
+
 		final int newSize = oldSize - removeCount;
 
-		// shift surviving elements left over the spaces left by removed elements
-		for (int i = 0, j = 0; (i < oldSize) && (j < newSize); i++, j++) {
-			i = deleted.nextClearBit(i);
+		// Punch out the deleted instances, shifting over surviving instances to fill their place.
+		for (int scanPos = 0, writePos = 0; (scanPos < oldSize) && (writePos < newSize); scanPos++, writePos++) {
+			// Find next non-deleted element.
+			scanPos = deleted.nextClearBit(scanPos);
 
-			if (i != j) {
-				var handle = handles.get(i);
-				I instance = instances.get(i);
+			if (scanPos != writePos) {
+				// Grab the old instance/handle from scanPos...
+				var handle = handles.get(scanPos);
+				I instance = instances.get(scanPos);
 
-				handles.set(j, handle);
-				instances.set(j, instance);
+				// ... and move it to writePos.
+				handles.set(writePos, handle);
+				instances.set(writePos, instance);
 
-				handle.index = j;
-				changed.set(j);
+				// Make sure the handle knows it's been moved...
+				handle.index = writePos;
+				// ...and set it changed to force an upload.
+				changed.set(writePos);
+
+				// Clear the old slot. There's nothing meaningful there that can be considered "changed".
+				changed.clear(scanPos);
 			}
 		}
 

src/main/java/com/jozufozu/flywheel/backend/engine/InstanceHandleImpl.java

@@ -19,6 +19,8 @@ public class InstanceHandleImpl implements InstanceHandle {
 	@Override
 	public void setDeleted() {
 		instancer.notifyRemoval(index);
+		// invalidate ourselves
+		clear();
 	}
 
 	public void clear() {

src/main/java/com/jozufozu/flywheel/backend/engine/indirect/IndirectEngine.java

@@ -76,26 +76,9 @@ public class IndirectEngine extends AbstractEngine {
 		executor.syncUntil(flushFlag::isRaised);
 
 		try (var restoreState = GlStateTracker.getRestoreState()) {
-			int prevActiveTexture = GlStateManager._getActiveTexture();
-			Minecraft.getInstance().gameRenderer.overlayTexture()
-					.setupOverlayColor();
-			Minecraft.getInstance().gameRenderer.lightTexture()
-					.turnOnLightLayer();
-
-			GlTextureUnit.T1.makeActive();
-			RenderSystem.bindTexture(RenderSystem.getShaderTexture(1));
-			GlTextureUnit.T2.makeActive();
-			RenderSystem.bindTexture(RenderSystem.getShaderTexture(2));
-
 			drawManager.renderCrumbling(crumblingBlocks);
 
 			MaterialRenderState.reset();
-
-			Minecraft.getInstance().gameRenderer.overlayTexture()
-					.teardownOverlayColor();
-			Minecraft.getInstance().gameRenderer.lightTexture()
-					.turnOffLightLayer();
-			GlStateManager._activeTexture(prevActiveTexture);
 		}
 	}
 

src/main/java/com/jozufozu/flywheel/lib/util/AtomicBitset.java

@@ -168,13 +168,13 @@ public class AtomicBitset {
 			if (++longPosition > segmentMask) {
 				segmentPosition++;
 				if (segmentPosition >= segments.numSegments()) {
-					return segments.numSegments() << log2SegmentSize;
+					return segments.numSegments() << log2SegmentSize + (longPosition << 6);
 				}
 				segment = segments.getSegment(segmentPosition);
 				longPosition = 0;
 			}
 
-			word = segment.get(longPosition);
+			word = ~segment.get(longPosition);
 		}
 	}
 

src/test/java/com/jozufozu/flywheel/lib/util/TestAtomicBitset.java

@@ -0,0 +1,40 @@
+package com.jozufozu.flywheel.lib.util;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TestAtomicBitset {
+
+	@Test
+	void testNextClearBit() {
+		var segmentLength = 1 << AtomicBitset.DEFAULT_LOG2_SEGMENT_SIZE_IN_BITS;
+		var bitLength = 2 << AtomicBitset.DEFAULT_LOG2_SEGMENT_SIZE_IN_BITS;
+		var bs = new AtomicBitset(AtomicBitset.DEFAULT_LOG2_SEGMENT_SIZE_IN_BITS, bitLength);
+
+		Assertions.assertEquals(0, bs.nextClearBit(0));
+		Assertions.assertEquals(1, bs.nextClearBit(1));
+
+		Assertions.assertEquals(5000, bs.nextClearBit(5000));
+
+		bs.set(16);
+
+		Assertions.assertEquals(0, bs.nextClearBit(0));
+		Assertions.assertEquals(17, bs.nextClearBit(16));
+
+		bs.set(segmentLength + 1);
+
+		Assertions.assertEquals(0, bs.nextClearBit(0));
+		Assertions.assertEquals(segmentLength + 2, bs.nextClearBit(segmentLength + 1));
+
+		bs.set(bitLength);
+
+		Assertions.assertEquals(0, bs.nextClearBit(0));
+		Assertions.assertEquals(bitLength + 1, bs.nextClearBit(bitLength));
+
+		for (int i = 0; i < bitLength; i++) {
+			bs.set(i);
+		}
+
+		Assertions.assertEquals(bitLength + 1, bs.nextClearBit(0));
+	}
+}