First try

- Fix race condition causing instancers to never be initialized
- Fix frame uniforms being 8 bytes too small
- Don't have any bias in BakedModelBufferer#bufferItem, instead sort
  meshes with glint transparency to be rendered last
- Only visualized item entities if their items are supported
- Key item models directly on the BakedModel + if the stack has foil

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

@@ -4,7 +4,9 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Queue;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentLinkedQueue;
 
 import com.jozufozu.flywheel.Flywheel;
 import com.jozufozu.flywheel.api.backend.Engine;
@@ -32,7 +34,7 @@ public abstract class DrawManager<N extends AbstractInstancer<?>> {
 	 * <br>
 	 * All new instancers land here before having resources allocated in {@link #flush}.
 	 */
-	protected final List<UninitializedInstancer<N, ?>> initializationQueue = new ArrayList<>();
+	protected final Queue<UninitializedInstancer<N, ?>> initializationQueue = new ConcurrentLinkedQueue<>();
 
 	@SuppressWarnings("unchecked")
 	public <I extends Instance> Instancer<I> getInstancer(Environment environment, InstanceType<I> type, Model model, RenderStage stage) {
@@ -72,7 +74,8 @@ public abstract class DrawManager<N extends AbstractInstancer<?>> {
 		// Only queue the instancer for initialization if it has anything to render.
 		if (checkAndWarnEmptyModel(key.model())) {
 			// Thread safety: this method is called atomically from within computeIfAbsent,
-			// so we don't need extra synchronization to protect the queue.
+			// so you'd think we don't need extra synchronization to protect the queue, but
+			// somehow threads can race here and wind up never initializing an instancer.
 			initializationQueue.add(new UninitializedInstancer<>(key, out));
 		}
 		return out;

src/main/java/com/jozufozu/flywheel/backend/engine/uniform/FrameUniforms.java

@@ -19,7 +19,7 @@ import net.minecraft.world.level.Level;
 import net.minecraft.world.phys.Vec3;
 
 public class FrameUniforms implements UniformProvider {
-	public static final int SIZE = 800;
+	public static final int SIZE = 808;
 	public int debugMode;
 
 	@Nullable

src/main/java/com/jozufozu/flywheel/lib/model/baked/BakedModelBufferer.java

@@ -1,8 +1,6 @@
 package com.jozufozu.flywheel.lib.model.baked;
 
-import java.util.HashMap;
 import java.util.Iterator;
-import java.util.LinkedHashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
@@ -14,6 +12,8 @@ import com.mojang.blaze3d.vertex.BufferBuilder.RenderedBuffer;
 import com.mojang.blaze3d.vertex.PoseStack;
 import com.mojang.blaze3d.vertex.VertexConsumer;
 
+import it.unimi.dsi.fastutil.objects.Reference2ReferenceOpenHashMap;
+import it.unimi.dsi.fastutil.objects.ReferenceArraySet;
 import net.minecraft.client.Minecraft;
 import net.minecraft.client.renderer.ItemBlockRenderTypes;
 import net.minecraft.client.renderer.MultiBufferSource;
@@ -150,10 +150,9 @@ final class BakedModelBufferer {
 		var emitterSource = objects.emitterSource;
 		emitterSource.resultConsumer(consumer);
 
-		var itemRenderer = Minecraft.getInstance()
+		Minecraft.getInstance()
-				.getItemRenderer();
+				.getItemRenderer()
-
+				.render(stack, displayContext, leftHand, poseStack, emitterSource, 0, OverlayTexture.NO_OVERLAY, model);
-		itemRenderer.render(stack, displayContext, leftHand, poseStack, emitterSource, 0, OverlayTexture.NO_OVERLAY, model);
 
 		emitterSource.end();
 	}
@@ -182,11 +181,8 @@ final class BakedModelBufferer {
 	}
 
 	private static class MeshEmitterSource implements MultiBufferSource {
-		private final Map<RenderType, MeshEmitter> emitters = new HashMap<>();
+		private final Map<RenderType, MeshEmitter> emitters = new Reference2ReferenceOpenHashMap<>();
-
+		private final Set<MeshEmitter> active = new ReferenceArraySet<>();
-		private final Set<MeshEmitter> active = new LinkedHashSet<>();
-		// Hack: we want glint to render after everything else so track it separately here
-		private final Set<MeshEmitter> activeGlint = new LinkedHashSet<>();
 
 		@Nullable
 		private ResultConsumer resultConsumer;
@@ -195,13 +191,6 @@ final class BakedModelBufferer {
 		public VertexConsumer getBuffer(RenderType renderType) {
 			var out = emitters.computeIfAbsent(renderType, type -> new MeshEmitter(new BufferBuilder(type.bufferSize()), type));
 
-			Set<MeshEmitter> active;
-			if (renderType == RenderType.glint() || renderType == RenderType.glintDirect() || renderType == RenderType.entityGlint() || renderType == RenderType.entityGlintDirect()) {
-				active = this.activeGlint;
-			} else {
-				active = this.active;
-			}
-
 			if (active.add(out)) {
 				out.begin(resultConsumer);
 			}
@@ -214,12 +203,7 @@ final class BakedModelBufferer {
 				emitter.end();
 			}
 
-			for (var emitter : activeGlint) {
-				emitter.end();
-			}
-
 			active.clear();
-			activeGlint.clear();
 
 			resultConsumer = null;
 		}

src/main/java/com/jozufozu/flywheel/lib/model/baked/ItemModelBuilder.java

@@ -1,11 +1,14 @@
 package com.jozufozu.flywheel.lib.model.baked;
 
+import java.util.ArrayList;
+import java.util.Comparator;
 import java.util.function.BiFunction;
 
 import org.jetbrains.annotations.Nullable;
 
 import com.google.common.collect.ImmutableList;
 import com.jozufozu.flywheel.api.material.Material;
+import com.jozufozu.flywheel.api.material.Transparency;
 import com.jozufozu.flywheel.api.model.Model;
 import com.jozufozu.flywheel.api.vertex.VertexView;
 import com.jozufozu.flywheel.lib.memory.MemoryBlock;
@@ -16,24 +19,35 @@ import com.jozufozu.flywheel.lib.model.baked.BakedModelBufferer.ResultConsumer;
 import com.jozufozu.flywheel.lib.vertex.NoOverlayVertexView;
 import com.mojang.blaze3d.vertex.PoseStack;
 
-import net.minecraft.client.Minecraft;
 import net.minecraft.client.renderer.RenderType;
+import net.minecraft.client.resources.model.BakedModel;
 import net.minecraft.world.item.ItemDisplayContext;
 import net.minecraft.world.item.ItemStack;
 
 public class ItemModelBuilder {
+	public static final Comparator<Model.ConfiguredMesh> GLINT_LAST = (a, b) -> {
+		if (a.material()
+				.transparency() == b.material()
+				.transparency()) {
+			return 0;
+		}
+		return a.material()
+				.transparency() == Transparency.GLINT ? 1 : -1;
+	};
+
 	private final ItemStack itemStack;
+	private final BakedModel model;
 	@Nullable
 	private PoseStack poseStack;
 	@Nullable
 	private ItemDisplayContext displayContext;
 	private boolean leftHand;
-	private int seed = 42;
 	@Nullable
 	private BiFunction<RenderType, Boolean, Material> materialFunc;
 
-	public ItemModelBuilder(ItemStack itemStack) {
+	public ItemModelBuilder(ItemStack itemStack, BakedModel model) {
 		this.itemStack = itemStack;
+		this.model = model;
 	}
 
 	public ItemModelBuilder poseStack(PoseStack poseStack) {
@@ -51,11 +65,6 @@ public class ItemModelBuilder {
 		return this;
 	}
 
-	public ItemModelBuilder seed(int seed) {
-		this.seed = seed;
-		return this;
-	}
-
 	public ItemModelBuilder materialFunc(BiFunction<RenderType, Boolean, Material> materialFunc) {
 		this.materialFunc = materialFunc;
 		return this;
@@ -69,7 +78,7 @@ public class ItemModelBuilder {
 			materialFunc = ModelUtil::getItemMaterial;
 		}
 
-		var out = ImmutableList.<Model.ConfiguredMesh>builder();
+		ArrayList<Model.ConfiguredMesh> out = new ArrayList<>();
 
 		ResultConsumer resultConsumer = (renderType, shaded, data) -> {
 			Material material = materialFunc.apply(renderType, shaded);
@@ -77,16 +86,19 @@ public class ItemModelBuilder {
 				VertexView vertexView = new NoOverlayVertexView();
 				MemoryBlock meshData = ModelUtil.convertVanillaBuffer(data, vertexView);
 				var mesh = new SimpleMesh(vertexView, meshData, "source=ItemModelBuilder," + "itemStack=" + itemStack + ",renderType=" + renderType + ",shaded=" + shaded);
-				out.add(new Model.ConfiguredMesh(material, mesh));
+				if (mesh.vertexCount() == 0) {
+					mesh.delete();
+					return;
+				} else {
+					out.add(new Model.ConfiguredMesh(material, mesh));
+				}
 			}
 		};
 
-		var model = Minecraft.getInstance()
-				.getItemRenderer()
-				.getModel(itemStack, null, null, seed);
-
 		BakedModelBufferer.bufferItem(model, itemStack, displayContext, leftHand, poseStack, resultConsumer);
 
-		return new SimpleModel(out.build());
+		out.sort(GLINT_LAST);
+
+		return new SimpleModel(ImmutableList.copyOf(out));
 	}
 }

src/main/java/com/jozufozu/flywheel/vanilla/ItemVisual.java

@@ -19,6 +19,9 @@ import com.mojang.math.Axis;
 import net.minecraft.client.Minecraft;
 import net.minecraft.client.renderer.LightTexture;
 import net.minecraft.client.resources.model.BakedModel;
+import net.minecraft.client.resources.model.MultiPartBakedModel;
+import net.minecraft.client.resources.model.SimpleBakedModel;
+import net.minecraft.client.resources.model.WeightedBakedModel;
 import net.minecraft.util.Mth;
 import net.minecraft.util.RandomSource;
 import net.minecraft.world.entity.item.ItemEntity;
@@ -32,23 +35,56 @@ public class ItemVisual extends SimpleEntityVisual<ItemEntity> {
 	private static final ThreadLocal<RandomSource> RANDOM = ThreadLocal.withInitial(RandomSource::createNewThreadLocalInstance);
 
 	public static final ModelCache<ItemKey> MODEL_CACHE = new ModelCache<>(stack -> {
-		return new ItemModelBuilder(stack.stack()).build();
+		return new ItemModelBuilder(stack.stack(), stack.model()).build();
 	});
 
 	private final PoseStack pPoseStack = new PoseStack();
 	private final BakedModel model;
+	private final boolean isSupported;
 
 	private final InstanceRecycler<TransformedInstance> instances;
 
 	public ItemVisual(VisualizationContext ctx, ItemEntity entity) {
 		super(ctx, entity);
 
+		var item = entity.getItem();
 		model = Minecraft.getInstance()
+				.getItemRenderer()
+				.getModel(item, entity.level(), null, entity.getId());
+
+		isSupported = isSupported(model);
+
+		var key = new ItemKey(item.copy(), model);
+
+		instances = new InstanceRecycler<>(() -> instancerProvider.instancer(InstanceTypes.TRANSFORMED, MODEL_CACHE.get(key))
+				.createInstance());
+	}
+
+	public static boolean isSupported(ItemEntity entity) {
+		var model = Minecraft.getInstance()
 				.getItemRenderer()
 				.getModel(entity.getItem(), entity.level(), null, entity.getId());
 
-		instances = new InstanceRecycler<>(() -> instancerProvider.instancer(InstanceTypes.TRANSFORMED, MODEL_CACHE.get(new ItemKey(entity.getItem())))
+		return isSupported(model);
-				.createInstance());
+	}
+
+	public static boolean isSupported(BakedModel model) {
+		if (model.isCustomRenderer()) {
+			return false;
+		}
+
+		if (!model.getOverrides()
+				.getOverrides()
+				.isEmpty()) {
+			return false;
+		}
+
+		Class<? extends BakedModel> c = model.getClass();
+		if (!(c == SimpleBakedModel.class || c == MultiPartBakedModel.class || c == WeightedBakedModel.class)) {
+			return false;
+		}
+
+		return true;
 	}
 
 	@Override
@@ -63,7 +99,7 @@ public class ItemVisual extends SimpleEntityVisual<ItemEntity> {
 
 	@Override
 	public void beginFrame(Context ctx) {
-		if (!isVisible(ctx.frustum())) {
+		if (!isSupported || !isVisible(ctx.frustum())) {
 			return;
 		}
 
@@ -162,11 +198,7 @@ public class ItemVisual extends SimpleEntityVisual<ItemEntity> {
 		instances.delete();
 	}
 
-	public record ItemKey(ItemStack stack) {
+	public record ItemKey(ItemStack stack, BakedModel model) {
-		public ItemKey(ItemStack stack) {
-			this.stack = stack.copy();
-		}
-
 
 		@Override
 		public boolean equals(Object o) {
@@ -177,20 +209,14 @@ public class ItemVisual extends SimpleEntityVisual<ItemEntity> {
 				return false;
 			}
 
-			ItemKey itemKey = (ItemKey) o;
+			var o1 = (ItemKey) o;
-			if (stack.isEmpty()) {
+			return Objects.equals(model, o1.model) && stack.hasFoil() == o1.stack.hasFoil();
-				return itemKey.stack.isEmpty();
-			} else {
-				return !itemKey.stack.isEmpty() && stack.getItem() == itemKey.stack.getItem() && Objects.equals(stack.getTag(), itemKey.stack.getTag());
-			}
 		}
 
 		@Override
 		public int hashCode() {
-			int out = stack.getItem()
+			int out = model.hashCode();
-					.hashCode();
+			out = 31 * out + Boolean.hashCode(stack.hasFoil());
-			out = 31 * out + (stack.getTag() != null ? stack.getTag()
-					.hashCode() : 0);
 			return out;
 		}
 	}

src/main/java/com/jozufozu/flywheel/vanilla/VanillaVisuals.java

@@ -79,6 +79,7 @@ public class VanillaVisuals {
 				.apply();
 
 		builder(EntityType.ITEM).factory(ItemVisual::new)
+				.skipVanillaRender(ItemVisual::isSupported)
 				.apply();
 	}
 }