Naive parallelism

- Submit many tasks to executor and then wait for them all to complete.
 - Use WaitGroup
 - SBB no longer stores params, instead accepts Params arg to render
 - SBB keeps scratch variables local
 - CPUInstancer keeps track of default params
 - Separate #setup and #draw... functions in CPUInstancer
 - Combine DirectBufferBuilder#updateAfterWriting with #intoDirectConsumer
 - DirectVertexConsumer#split to distribute work

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

@@ -66,6 +66,10 @@ public abstract class AbstractInstancer<D extends InstanceData> implements Insta
 		return data.size();
 	}
 
+	public int getTotalVertexCount() {
+		return getModelVertexCount() * numInstances();
+	}
+
 	protected BitSet getDirtyBitSet() {
 		final int size = data.size();
 		final BitSet dirtySet = new BitSet(size);

src/main/java/com/jozufozu/flywheel/backend/instancing/batching/BatchExecutor.java

@@ -0,0 +1,34 @@
+package com.jozufozu.flywheel.backend.instancing.batching;
+
+import java.util.concurrent.Executor;
+
+import org.jetbrains.annotations.NotNull;
+
+public class BatchExecutor implements Executor {
+	private final Executor internal;
+	private final WaitGroup wg;
+
+	public BatchExecutor(Executor internal) {
+		this.internal = internal;
+
+		wg = new WaitGroup();
+	}
+
+	@Override
+	public void execute(@NotNull Runnable command) {
+		wg.add(1);
+		internal.execute(() -> {
+			// wrapper function to decrement the wait group
+			try {
+				command.run();
+			} catch (Exception ignored) {
+			} finally {
+				wg.done();
+			}
+		});
+	}
+
+	public void await() throws InterruptedException {
+		wg.await();
+	}
+}

src/main/java/com/jozufozu/flywheel/backend/instancing/batching/BatchedMaterial.java

@@ -30,7 +30,8 @@ public class BatchedMaterial<D extends InstanceData> implements Material<D> {
 
 	public void render(PoseStack stack, VertexConsumer buffer, FormatContext context) {
 		for (CPUInstancer<D> instancer : models.values()) {
-			instancer.drawAll(stack, buffer, context);
+			instancer.setup(context);
+			instancer.drawAll(stack, buffer);
 		}
 	}
 

src/main/java/com/jozufozu/flywheel/backend/instancing/batching/BatchedMaterialGroup.java

@@ -2,6 +2,7 @@ package com.jozufozu.flywheel.backend.instancing.batching;
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.Executor;
 
 import com.jozufozu.flywheel.api.InstanceData;
 import com.jozufozu.flywheel.api.MaterialGroup;
@@ -30,15 +31,20 @@ public class BatchedMaterialGroup implements MaterialGroup {
 		return (BatchedMaterial<D>) materials.computeIfAbsent(spec, BatchedMaterial::new);
 	}
 
-	public void render(PoseStack stack, MultiBufferSource source) {
+	public void render(PoseStack stack, MultiBufferSource source, Executor pool) {
 		VertexConsumer buffer = source.getBuffer(state);
 
 		if (buffer instanceof DirectBufferBuilder direct) {
 			DirectVertexConsumer consumer = direct.intoDirectConsumer(calculateNeededVertices());
+			FormatContext context = new FormatContext(consumer.hasOverlay());
 
-			renderInto(stack, consumer, new FormatContext(consumer.hasOverlay()));
+			for (BatchedMaterial<?> material : materials.values()) {
+				for (CPUInstancer<?> instancer : material.models.values()) {
+					instancer.setup(context);
 
-			direct.updateAfterWriting(consumer);
+					instancer.submitTasks(stack, pool, consumer);
+				}
+			}
 		} else {
 			renderInto(stack, buffer, FormatContext.defaultContext());
 		}
@@ -48,7 +54,7 @@ public class BatchedMaterialGroup implements MaterialGroup {
 		int total = 0;
 		for (BatchedMaterial<?> material : materials.values()) {
 			for (CPUInstancer<?> instancer : material.models.values()) {
-				total += instancer.getModelVertexCount() * instancer.numInstances();
+				total += instancer.getTotalVertexCount();
 			}
 		}
 

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

@@ -3,6 +3,8 @@ package com.jozufozu.flywheel.backend.instancing.batching;
 import java.util.EnumMap;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ForkJoinPool;
 
 import com.jozufozu.flywheel.api.MaterialGroup;
 import com.jozufozu.flywheel.backend.RenderLayer;
@@ -22,11 +24,15 @@ public class BatchingEngine implements Engine {
 
 	protected final Map<RenderLayer, Map<RenderType, BatchedMaterialGroup>> layers;
 
+	private final BatchExecutor pool;
+
 	public BatchingEngine() {
 		this.layers = new EnumMap<>(RenderLayer.class);
 		for (RenderLayer value : RenderLayer.values()) {
 			layers.put(value, new HashMap<>());
 		}
+
+		pool = new BatchExecutor(Executors.newWorkStealingPool(ForkJoinPool.getCommonPoolParallelism()));
 	}
 
 	@Override
@@ -50,7 +56,12 @@ public class BatchingEngine implements Engine {
 		for (Map.Entry<RenderType, BatchedMaterialGroup> entry : layers.get(event.getLayer()).entrySet()) {
 			BatchedMaterialGroup group = entry.getValue();
 
-			group.render(stack, buffers);
+			group.render(stack, buffers, pool);
+		}
+
+		try {
+			pool.await();
+		} catch (InterruptedException ignored) {
 		}
 
 		stack.popPose();

src/main/java/com/jozufozu/flywheel/backend/instancing/batching/CPUInstancer.java

@@ -1,27 +1,51 @@
 package com.jozufozu.flywheel.backend.instancing.batching;
 
+import java.util.concurrent.Executor;
+
 import com.jozufozu.flywheel.api.InstanceData;
 import com.jozufozu.flywheel.api.struct.BatchingTransformer;
 import com.jozufozu.flywheel.api.struct.StructType;
 import com.jozufozu.flywheel.backend.instancing.AbstractInstancer;
+import com.jozufozu.flywheel.backend.model.DirectVertexConsumer;
 import com.jozufozu.flywheel.core.model.Model;
 import com.jozufozu.flywheel.core.model.SuperByteBuffer;
 import com.mojang.blaze3d.vertex.PoseStack;
 import com.mojang.blaze3d.vertex.VertexConsumer;
-import com.mojang.blaze3d.vertex.VertexFormat;
 
 public class CPUInstancer<D extends InstanceData> extends AbstractInstancer<D> {
 
 	private final BatchingTransformer<D> transform;
 
 	private final SuperByteBuffer sbb;
+	private final SuperByteBuffer.Params defaultParams;
 
 	public CPUInstancer(StructType<D> type, Model modelData) {
 		super(type, modelData);
 
 		sbb = new SuperByteBuffer(modelData);
+		defaultParams = SuperByteBuffer.Params.defaultParams();
 		transform = type.asBatched()
 				.getTransformer();
+
+		if (transform == null) {
+			throw new NullPointerException("Cannot batch " + type.toString());
+		}
+	}
+
+	void submitTasks(PoseStack stack, Executor pool, DirectVertexConsumer consumer) {
+		int instances = numInstances();
+
+		while (instances > 0) {
+			int end = instances;
+			instances -= 100;
+			int start = Math.max(instances, 0);
+
+			int verts = getModelVertexCount() * (end - start);
+
+			DirectVertexConsumer sub = consumer.split(verts);
+
+			pool.execute(() -> drawRange(stack, sub, start, end));
+		}
 	}
 
 	@Override
@@ -29,23 +53,34 @@ public class CPUInstancer<D extends InstanceData> extends AbstractInstancer<D> {
 		// noop
 	}
 
-	public void drawAll(PoseStack stack, VertexConsumer buffer, FormatContext context) {
-		if (transform == null) {
-			return;
-		}
+	private void drawRange(PoseStack stack, VertexConsumer buffer, int from, int to) {
+		SuperByteBuffer.Params params = defaultParams.copy();
 
+		for (D d : data.subList(from, to)) {
+			transform.transform(d, params);
+
+			sbb.renderInto(params, stack, buffer);
+
+			params.load(defaultParams);
+		}
+	}
+
+	void drawAll(PoseStack stack, VertexConsumer buffer) {
+		SuperByteBuffer.Params params = defaultParams.copy();
+		for (D d : data) {
+			transform.transform(d, params);
+
+			sbb.renderInto(params, stack, buffer);
+
+			params.load(defaultParams);
+		}
+	}
+
+	void setup(FormatContext context) {
 		renderSetup();
 
 		if (context.usesOverlay()) {
-			sbb.getDefaultParams().entityMode();
-		}
-
-		sbb.reset();
-
-		for (D d : data) {
-			transform.transform(d, sbb.getParams());
-
-			sbb.renderInto(stack, buffer);
+			defaultParams.entityMode();
 		}
 	}
 

src/main/java/com/jozufozu/flywheel/backend/instancing/batching/WaitGroup.java

@@ -0,0 +1,24 @@
+package com.jozufozu.flywheel.backend.instancing.batching;
+
+// https://stackoverflow.com/questions/29655531
+public class WaitGroup {
+
+	private int jobs = 0;
+
+	public synchronized void add(int i) {
+		jobs += i;
+	}
+
+	public synchronized void done() {
+		if (--jobs == 0) {
+			notifyAll();
+		}
+	}
+
+	public synchronized void await() throws InterruptedException {
+		while (jobs > 0) {
+			wait();
+		}
+	}
+
+}

src/main/java/com/jozufozu/flywheel/backend/model/DirectBufferBuilder.java

@@ -2,7 +2,5 @@ package com.jozufozu.flywheel.backend.model;
 
 public interface DirectBufferBuilder {
 
-	DirectVertexConsumer intoDirectConsumer(int neededVerts);
-
-	void updateAfterWriting(DirectVertexConsumer complete);
+	DirectVertexConsumer intoDirectConsumer(int vertexCount);
 }

src/main/java/com/jozufozu/flywheel/backend/model/DirectVertexConsumer.java

@@ -10,7 +10,6 @@ import com.mojang.blaze3d.vertex.VertexFormat;
 import com.mojang.blaze3d.vertex.VertexFormatElement;
 
 public class DirectVertexConsumer implements VertexConsumer {
-
 	public final VertexFormat format;
 	private final int stride;
 	public final int startPos;
@@ -23,7 +22,6 @@ public class DirectVertexConsumer implements VertexConsumer {
 	private int uv2 = -1;
 
 	private long vertexBase;
-	private int vertexCount;
 
 	public DirectVertexConsumer(ByteBuffer buffer, VertexFormat format) {
 		this.format = format;
@@ -49,13 +47,42 @@ public class DirectVertexConsumer implements VertexConsumer {
 			offset += element.getByteSize();
 		}
 
-		this.vertexBase = MemoryUtil.memAddress(buffer);
+		this.vertexBase = MemoryUtil.memAddress(buffer, startPos);
+	}
+
+	private DirectVertexConsumer(DirectVertexConsumer parent) {
+		this.format = parent.format;
+		this.stride = parent.stride;
+		this.startPos = parent.startPos;
+		this.position = parent.position;
+		this.normal = parent.normal;
+		this.color = parent.color;
+		this.uv = parent.uv;
+		this.uv1 = parent.uv1;
+		this.uv2 = parent.uv2;
+
+		this.vertexBase = parent.vertexBase;
 	}
 
 	public boolean hasOverlay() {
 		return uv1 >= 0;
 	}
 
+	/**
+	 * Split off the head of this consumer into a new object and advance our write-pointer.
+	 * @param vertexCount The number of vertices that must be written to the head.
+	 * @return The head of this consumer.
+	 */
+	public DirectVertexConsumer split(int vertexCount) {
+		int bytes = vertexCount * stride;
+
+		DirectVertexConsumer head = new DirectVertexConsumer(this);
+
+		this.vertexBase += bytes;
+
+		return head;
+	}
+
 	@Override
 	public VertexConsumer vertex(double x, double y, double z) {
 		if (position < 0) return this;
@@ -117,7 +144,6 @@ public class DirectVertexConsumer implements VertexConsumer {
 	@Override
 	public void endVertex() {
 		vertexBase += stride;
-		vertexCount++;
 	}
 
 	@Override
@@ -129,8 +155,4 @@ public class DirectVertexConsumer implements VertexConsumer {
 	public void unsetDefaultColor() {
 
 	}
-
-	public int getVertexCount() {
-		return vertexCount;
-	}
 }

src/main/java/com/jozufozu/flywheel/core/model/SuperByteBuffer.java

@@ -22,32 +22,22 @@ public class SuperByteBuffer {
 	private final Model model;
 	private final ModelReader template;
 
-	private final Params defaultParams = Params.defaultParams();
-	private final Params params = defaultParams.copy();
-
-	public Params getDefaultParams() {
-		return defaultParams;
-	}
-
-	public Params getParams() {
-		return params;
-	}
-
 	// Temporary
 	private static final Long2IntMap WORLD_LIGHT_CACHE = new Long2IntOpenHashMap();
-	private final Vector4f pos = new Vector4f();
-	private final Vector3f normal = new Vector3f();
-	private final Vector4f lightPos = new Vector4f();
 
 	public SuperByteBuffer(Model model) {
 		this.model = model;
 		template = model.getReader();
 	}
 
-	public void renderInto(PoseStack input, VertexConsumer builder) {
+	public void renderInto(Params params, PoseStack input, VertexConsumer builder) {
 		if (isEmpty())
 			return;
 
+		Vector4f pos = new Vector4f();
+		Vector3f normal = new Vector3f();
+		Vector4f lightPos = new Vector4f();
+
 		Matrix4f modelMat = input.last()
 				.pose()
 				.copy();
@@ -168,14 +158,6 @@ public class SuperByteBuffer {
 
 			builder.endVertex();
 		}
-
-		reset();
-	}
-
-	public SuperByteBuffer reset() {
-		params.load(defaultParams);
-
-		return this;
 	}
 
 	public boolean isEmpty() {

src/main/java/com/jozufozu/flywheel/mixin/BufferBuilderMixin.java

@@ -38,21 +38,19 @@ public abstract class BufferBuilderMixin implements DirectBufferBuilder {
 	private int nextElementByte;
 
 	@Override
-	public DirectVertexConsumer intoDirectConsumer(int neededVerts) {
-		ensureCapacity(neededVerts * this.format.getVertexSize());
-		return new DirectVertexConsumer(this.buffer, this.format);
-	}
+	public DirectVertexConsumer intoDirectConsumer(int vertexCount) {
+		int bytes = vertexCount * format.getVertexSize();
+		ensureCapacity(bytes);
 
-	@Override
-	public void updateAfterWriting(DirectVertexConsumer complete) {
-		int vertexCount = complete.getVertexCount();
-		int totalWrittenBytes = vertexCount * format.getVertexSize();
+		DirectVertexConsumer consumer = new DirectVertexConsumer(this.buffer, this.format);
 
 		this.vertices += vertexCount;
 		this.currentElement = format.getElements()
 				.get(0);
 		this.elementIndex = 0;
-		this.nextElementByte += totalWrittenBytes;
-		this.buffer.position(complete.startPos + totalWrittenBytes);
+		this.nextElementByte += bytes;
+		this.buffer.position(consumer.startPos + bytes);
+
+		return consumer;
 	}
 }