Bookkeeping

- Mappings drop pages when they write zero validity bits
- Instancer only updates pages that changed

common/src/backend/java/dev/engine_room/flywheel/backend/engine/indirect/IndirectInstancer.java

@@ -168,7 +168,7 @@ public int takeFrom(InstancePage other) {
 			int otherValid = other.valid.get();
 
 			// If the other page is empty, or we're full, we're done.
-			if (otherValid == 0 || valid == 0xFFFFFFFF) {
+			if (isEmpty(otherValid) || isFull(valid)) {
 				return valid;
 			}
 
@@ -223,15 +223,27 @@ public List<IndirectDraw> draws() {
 	public void update(int modelIndex, int baseInstance) {
 		this.baseInstance = baseInstance;
 
-		if (this.modelIndex == modelIndex && changedPages.isEmpty()) {
+		var sameModelIndex = this.modelIndex == modelIndex;
+		if (sameModelIndex && changedPages.isEmpty()) {
+			// Nothing to do!
 			return;
 		}
+
 		this.modelIndex = modelIndex;
+
 		var pages = this.pages.get();
 		mapping.updateCount(pages.length);
 
-		for (int i = 0; i < pages.length; i++) {
-			mapping.updatePage(i, modelIndex, pages[i].valid.get());
+		if (sameModelIndex) {
+			// Only need to update the changed pages.
+			for (int page = changedPages.nextSetBit(0); page >= 0 && page < pages.length; page = changedPages.nextSetBit(page + 1)) {
+				mapping.updatePage(page, modelIndex, pages[page].valid.get());
+			}
+		} else {
+			// Need to update all pages since the model index changed.
+			for (int i = 0; i < pages.length; i++) {
+				mapping.updatePage(i, modelIndex, pages[i].valid.get());
+			}
 		}
 	}
 
@@ -291,46 +303,17 @@ public void uploadInstances(StagingBuffer stagingBuffer, int instanceVbo) {
 	}
 
 	public void parallelUpdate() {
-		if (true) {
-			// FIXME: infinite loop when the page in readpos doesn't have enough to fill the page in writepos
-			return;
-		}
-
-		var pages = this.pages.get();
-
-		// If there are at least 2 pages with space, we can consolidate.
-		if (fullPages.cardinality() > (pages.length - 2)) {
-			return;
-		}
-
-		// Note this runs after visuals are updated so we don't really have to take care for thread safety.
-
-		int writePos = 0;
-
-		while (true) {
-			writePos = fullPages.nextClearBit(writePos);
-			int readPos = fullPages.nextClearBit(writePos + 1);
-
-			if (writePos >= pages.length || readPos >= pages.length) {
-				break;
-			}
-
-			InstancePage writeTo = pages[writePos];
-			InstancePage readFrom = pages[readPos];
-
-			int validNow = writeTo.takeFrom(readFrom);
-
-			if (isFull(validNow)) {
-				fullPages.set(writePos);
-				writePos = readPos;
-			}
-		}
+		// TODO: Merge pages when they're less than half full.
 	}
 
 	private static boolean isFull(int valid) {
 		return valid == 0xFFFFFFFF;
 	}
 
+	private static boolean isEmpty(int otherValid) {
+		return otherValid == 0;
+	}
+
 	@Override
 	public void delete() {
 		for (IndirectDraw draw : draws()) {

common/src/backend/java/dev/engine_room/flywheel/backend/engine/indirect/ObjectStorage.java

@@ -13,6 +13,8 @@ public class ObjectStorage extends AbstractArena {
 	public static final int PAGE_SIZE = 1 << LOG_2_PAGE_SIZE;
 	public static final int PAGE_MASK = PAGE_SIZE - 1;
 
+	public static final int INVALID_PAGE = -1;
+
 	public static final int INITIAL_PAGES_ALLOCATED = 4;
 	public static final int DESCRIPTOR_SIZE_BYTES = Integer.BYTES * 2;
 
@@ -53,8 +55,13 @@ public long byteCapacity() {
 
 	@Override
 	public void free(int i) {
+		if (i == INVALID_PAGE) {
+			return;
+		}
 		super.free(i);
-		MemoryUtil.memPutInt(ptrForPage(i), 0);
+		var ptr = ptrForPage(i);
+		MemoryUtil.memPutInt(ptr, 0);
+		MemoryUtil.memPutInt(ptr + 4, 0);
 	}
 
 	@Override
@@ -98,14 +105,49 @@ public class Mapping {
 		private static final int[] EMPTY_ALLOCATION = new int[0];
 		private int[] pages = EMPTY_ALLOCATION;
 
-		public void updatePage(int i, int modelIndex, int i1) {
-			var ptr = ptrForPage(pages[i]);
+		public void updatePage(int index, int modelIndex, int validBits) {
+			if (validBits == 0) {
+				holePunch(index);
+				return;
+			}
+			var page = pages[index];
+
+			if (page == INVALID_PAGE) {
+				// Un-holed punch.
+				page = unHolePunch(index);
+			}
+
+			var ptr = ptrForPage(page);
 			MemoryUtil.memPutInt(ptr, modelIndex);
-			MemoryUtil.memPutInt(ptr + 4, i1);
+			MemoryUtil.memPutInt(ptr + 4, validBits);
 
 			ObjectStorage.this.needsUpload = true;
 		}
 
+		/**
+		 * Free a page on the inside of the mapping, maintaining the same virtual mapping size.
+		 *
+		 * @param index The index of the page to free.
+		 */
+		public void holePunch(int index) {
+			ObjectStorage.this.free(pages[index]);
+			pages[index] = INVALID_PAGE;
+
+			ObjectStorage.this.needsUpload = true;
+		}
+
+		/**
+		 * Allocate a new page on the inside of the mapping, maintaining the same virtual mapping size.
+		 *
+		 * @param index The index of the page to allocate.
+		 * @return The allocated page.
+		 */
+		private int unHolePunch(int index) {
+			int page = ObjectStorage.this.alloc();
+			pages[index] = page;
+			return page;
+		}
+
 		public void updateCount(int newLength) {
 			var oldLength = pages.length;
 			if (oldLength > newLength) {
@@ -122,8 +164,8 @@ public int pageCount() {
 			return pages.length;
 		}
 
-		public long page2ByteOffset(int page) {
-			return ObjectStorage.this.byteOffsetOf(pages[page]);
+		public long page2ByteOffset(int index) {
+			return ObjectStorage.this.byteOffsetOf(pages[index]);
 		}
 
 		public void delete() {