So many draws

- Sort draws in an IndirectDrawSet by RenderStage and Material
- Loop through ahead of time and determine what individual draws can be
  grouped together into a MultiDraw
  - Contiguous segments with the same RenderStage and Material can be
    merged into one MultiDraw call
- Add material ID lookup for sorting purposes

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

@@ -2,7 +2,6 @@ package com.jozufozu.flywheel.backend.instancing;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;

src/main/java/com/jozufozu/flywheel/backend/instancing/indirect/IndirectCullingGroup.java

@@ -3,7 +3,13 @@ package com.jozufozu.flywheel.backend.instancing.indirect;
 import static org.lwjgl.opengl.GL42.GL_COMMAND_BARRIER_BIT;
 import static org.lwjgl.opengl.GL42.glMemoryBarrier;
 import static org.lwjgl.opengl.GL43.GL_SHADER_STORAGE_BARRIER_BIT;
-import static org.lwjgl.opengl.GL46.*;
+import static org.lwjgl.opengl.GL46.glBindVertexArray;
+import static org.lwjgl.opengl.GL46.glCreateVertexArrays;
+import static org.lwjgl.opengl.GL46.glDeleteVertexArrays;
+import static org.lwjgl.opengl.GL46.glDispatchCompute;
+import static org.lwjgl.opengl.GL46.glEnableVertexArrayAttrib;
+import static org.lwjgl.opengl.GL46.glVertexArrayElementBuffer;
+import static org.lwjgl.opengl.GL46.glVertexArrayVertexBuffer;
 
 import com.jozufozu.flywheel.api.RenderStage;
 import com.jozufozu.flywheel.api.instancer.InstancedPart;
@@ -142,7 +148,8 @@ public class IndirectCullingGroup<T extends InstancedPart> {
 
 		for (int i = 0, batchesSize = drawSet.indirectDraws.size(); i < batchesSize; i++) {
 			var batch = drawSet.indirectDraws.get(i);
-			var instanceCount = batch.instancer.getInstanceCount();
+			var instanceCount = batch.instancer()
+					.getInstanceCount();
 			batch.writeObjects(objectPtr, batchIDPtr, i);
 
 			objectPtr += instanceCount * objectStride;
@@ -166,7 +173,7 @@ public class IndirectCullingGroup<T extends InstancedPart> {
 		int baseInstance = 0;
 		for (var batch : drawSet.indirectDraws) {
 			batch.prepare(baseInstance);
-			baseInstance += batch.instancer.instanceCount;
+			baseInstance += batch.instancer().instanceCount;
 		}
 		return baseInstance;
 	}

src/main/java/com/jozufozu/flywheel/backend/instancing/indirect/IndirectDraw.java

@@ -8,10 +8,10 @@ import com.jozufozu.flywheel.api.material.Material;
 import com.jozufozu.flywheel.core.ComponentRegistry;
 
 public final class IndirectDraw<T extends InstancedPart> {
-	final IndirectInstancer<T> instancer;
-	final IndirectMeshPool.BufferedMesh mesh;
-	final Material material;
-	final RenderStage stage;
+	private final IndirectInstancer<T> instancer;
+	private final IndirectMeshPool.BufferedMesh mesh;
+	private final Material material;
+	private final RenderStage stage;
 	int baseInstance = -1;
 
 	final int vertexMaterialID;
@@ -62,4 +62,20 @@ public final class IndirectDraw<T extends InstancedPart> {
 		MemoryUtil.memPutInt(ptr + 40, fragmentMaterialID); // fragmentMaterialID
 
 	}
+
+	public IndirectInstancer<T> instancer() {
+		return instancer;
+	}
+
+	public IndirectMeshPool.BufferedMesh mesh() {
+		return mesh;
+	}
+
+	public Material material() {
+		return material;
+	}
+
+	public RenderStage stage() {
+		return stage;
+	}
 }

src/main/java/com/jozufozu/flywheel/backend/instancing/indirect/IndirectDrawSet.java

@@ -5,17 +5,23 @@ import static org.lwjgl.opengl.GL11.GL_UNSIGNED_INT;
 import static org.lwjgl.opengl.GL43.glMultiDrawElementsIndirect;
 
 import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumMap;
 import java.util.List;
+import java.util.Map;
 
 import com.jozufozu.flywheel.api.RenderStage;
 import com.jozufozu.flywheel.api.instancer.InstancedPart;
 import com.jozufozu.flywheel.api.material.Material;
+import com.jozufozu.flywheel.core.ComponentRegistry;
 import com.jozufozu.flywheel.util.Textures;
 
 public class IndirectDrawSet<T extends InstancedPart> {
 
 	final List<IndirectDraw<T>> indirectDraws = new ArrayList<>();
 
+	final Map<RenderStage, List<MultiDraw>> multiDraws = new EnumMap<>(RenderStage.class);
+
 	public boolean isEmpty() {
 		return indirectDraws.isEmpty();
 	}
@@ -26,31 +32,52 @@ public class IndirectDrawSet<T extends InstancedPart> {
 
 	public void add(IndirectInstancer<T> instancer, Material material, RenderStage stage, IndirectMeshPool.BufferedMesh bufferedMesh) {
 		indirectDraws.add(new IndirectDraw<>(instancer, material, stage, bufferedMesh));
+		determineMultiDraws();
 	}
 
 	public void submit(RenderStage stage) {
-		final int stride = (int) IndirectBuffers.DRAW_COMMAND_STRIDE;
-		for (int i = 0, indirectDrawsSize = indirectDraws.size(); i < indirectDrawsSize; i++) {
-			var batch = indirectDraws.get(i);
-			if (batch.stage != stage) {
-				continue;
+		if (!multiDraws.containsKey(stage)) {
+			return;
 		}
 
-			var material = batch.material;
-			material.setup();
-			Textures.bindActiveTextures();
-			glMultiDrawElementsIndirect(GL_TRIANGLES, GL_UNSIGNED_INT, i * stride, 1, stride);
-			material.clear();
+		for (var multiDraw : multiDraws.get(stage)) {
+			multiDraw.submit();
+		}
+	}
+
+	public void determineMultiDraws() {
+		// TODO: Better material equality. Really we only need to bin by the results of the setup method.
+		multiDraws.clear();
+		// sort by stage, then material
+		indirectDraws.sort(Comparator.comparing(IndirectDraw<T>::stage)
+				.thenComparing(draw -> ComponentRegistry.materials.getMaterialID(draw.material())));
+
+		for (int start = 0, i = 0; i < indirectDraws.size(); i++) {
+			var draw = indirectDraws.get(i);
+			var material = draw.material();
+			var stage = draw.stage();
+
+			// if the next draw call has a different RenderStage or Material, start a new MultiDraw
+			if (i == indirectDraws.size() - 1 || stage != indirectDraws.get(i + 1)
+					.stage() || !material.equals(indirectDraws.get(i + 1)
+					.material())) {
+				multiDraws.computeIfAbsent(stage, s -> new ArrayList<>())
+						.add(new MultiDraw(material, start, i + 1));
+				start = i + 1;
+			}
 		}
 	}
 
 	public boolean contains(RenderStage stage) {
-		for (var draw : indirectDraws) {
-			if (draw.stage == stage) {
-				return true;
-			}
+		return multiDraws.containsKey(stage);
 	}
 
-		return false;
+	private record MultiDraw(Material material, int start, int end) {
+		void submit() {
+			material.setup();
+			Textures.bindActiveTextures();
+			glMultiDrawElementsIndirect(GL_TRIANGLES, GL_UNSIGNED_INT, start * IndirectBuffers.DRAW_COMMAND_STRIDE, end - start, (int) IndirectBuffers.DRAW_COMMAND_STRIDE);
+			material.clear();
+		}
 	}
 }

src/main/java/com/jozufozu/flywheel/core/ComponentRegistry.java

@@ -83,14 +83,18 @@ public class ComponentRegistry {
 	public static class MaterialRegistry {
 
 		private final Set<Material> materials = new HashSet<>();
+		private final List<Material> materialsOrdered = new ArrayList<>();
 		private final MaterialSources vertexSources = new MaterialSources();
 		private final MaterialSources fragmentSources = new MaterialSources();
 
 		public <T extends Material> T add(T material) {
-			materials.add(material);
-
+			if (materials.add(material)) {
+				materialsOrdered.add(material);
 				vertexSources.register(material.vertexShader());
 				fragmentSources.register(material.fragmentShader());
+			} else {
+				throw new IllegalArgumentException("Material already registered: " + material);
+			}
 
 			return material;
 		}
@@ -117,6 +121,10 @@ public class ComponentRegistry {
 			return fragmentSources.orderedSources.indexOf(material.fragmentShader());
 		}
 
+		public int getMaterialID(Material material) {
+			return materialsOrdered.indexOf(material);
+		}
+
 		private static class MaterialSources {
 			private final Set<ResourceLocation> registered = new HashSet<>();
 			private final List<ResourceLocation> orderedSources = new ArrayList<>();