Errors and pools

- GlException and error checking WIP
 - Put all models within a material in a ModelPool
 - Instancers directly accept IModels
 - ModelPools are very WIP

src/main/java/com/jozufozu/flywheel/backend/gl/attrib/VertexAttribSpec.java

@@ -1,6 +1,8 @@
 package com.jozufozu.flywheel.backend.gl.attrib;
 
 import org.lwjgl.opengl.GL20;
+import org.lwjgl.opengl.GL44;
+import org.lwjgl.opengl.GL46;
 
 import com.jozufozu.flywheel.backend.gl.GlNumericType;
 

src/main/java/com/jozufozu/flywheel/backend/gl/buffer/MappedBufferRange.java

@@ -1,6 +1,9 @@
 package com.jozufozu.flywheel.backend.gl.buffer;
 
 import com.jozufozu.flywheel.backend.Backend;
+import com.jozufozu.flywheel.backend.gl.error.GlError;
+import com.jozufozu.flywheel.backend.gl.error.GlException;
+import com.jozufozu.flywheel.util.StringUtil;
 
 public class MappedBufferRange extends MappedBuffer {
 
@@ -27,6 +30,12 @@ public class MappedBufferRange extends MappedBuffer {
 	protected void checkAndMap() {
 		if (!mapped) {
 			setInternal(Backend.getInstance().compat.mapBufferRange.mapBuffer(owner.type, offset, length, access));
+
+			GlError error = GlError.poll();
+
+			if (error != null) {
+				throw new GlException(error, StringUtil.args("mapBufferRange", owner.type, offset, length, access));
+			}
 			mapped = true;
 		}
 	}

src/main/java/com/jozufozu/flywheel/backend/gl/buffer/MappedFullBuffer.java

@@ -2,6 +2,10 @@ package com.jozufozu.flywheel.backend.gl.buffer;
 
 import org.lwjgl.opengl.GL15;
 
+import com.jozufozu.flywheel.backend.gl.error.GlError;
+import com.jozufozu.flywheel.backend.gl.error.GlException;
+import com.jozufozu.flywheel.util.StringUtil;
+
 public class MappedFullBuffer extends MappedBuffer {
 
 	MappedBufferUsage usage;
@@ -15,6 +19,13 @@ public class MappedFullBuffer extends MappedBuffer {
 	protected void checkAndMap() {
 		if (!mapped) {
 			setInternal(GL15.glMapBuffer(owner.type.glEnum, usage.glEnum));
+
+			GlError error = GlError.poll();
+
+			if (error != null) {
+				throw new GlException(error, StringUtil.args("mapBuffer", owner.type, usage));
+			}
+
 			mapped = true;
 		}
 	}

src/main/java/com/jozufozu/flywheel/backend/gl/buffer/PersistentGlBuffer.java

@@ -6,6 +6,9 @@ import java.nio.ByteBuffer;
 
 import com.jozufozu.flywheel.backend.Backend;
 import com.jozufozu.flywheel.backend.gl.GlFence;
+import com.jozufozu.flywheel.backend.gl.error.GlError;
+import com.jozufozu.flywheel.backend.gl.error.GlException;
+import com.jozufozu.flywheel.util.StringUtil;
 
 
 public class PersistentGlBuffer extends GlBuffer {
@@ -35,11 +38,19 @@ public class PersistentGlBuffer extends GlBuffer {
 		if (buffer != null) {
 			deleteInternal(handle());
 			_create();
+
+			bind();
 		}
 
 		fence.clear();
 
-		Backend.getInstance().compat.bufferStorage.bufferStorage(type.glEnum, size, flags);
+		Backend.getInstance().compat.bufferStorage.bufferStorage(type, size, flags);
+
+		GlError error = GlError.poll();
+
+		if (error != null) {
+			throw new GlException(error, StringUtil.args("bufferStorage", type, size, flags));
+		}
 
 		buffer = new PersistentMappedBuffer(this);
 	}

src/main/java/com/jozufozu/flywheel/backend/gl/buffer/PersistentMappedBuffer.java

@@ -2,25 +2,42 @@ package com.jozufozu.flywheel.backend.gl.buffer;
 
 import java.nio.ByteBuffer;
 
-import org.lwjgl.opengl.GL15;
-import org.lwjgl.opengl.GL44;
-import org.lwjgl.opengl.GL46;
-
 import com.jozufozu.flywheel.backend.Backend;
+import com.jozufozu.flywheel.backend.gl.error.GlError;
+import com.jozufozu.flywheel.backend.gl.error.GlException;
+import com.jozufozu.flywheel.util.StringUtil;
 
 public class PersistentMappedBuffer extends MappedBuffer {
 
+	private final long offset;
+	private final long length;
 	PersistentGlBuffer owner;
 
 	public PersistentMappedBuffer(PersistentGlBuffer buffer) {
 		super(buffer);
 		owner = buffer;
+		offset = 0;
+		length = owner.size;
 
-		ByteBuffer byteBuffer = Backend.getInstance().compat.mapBufferRange.mapBuffer(owner.type, 0, owner.size, owner.flags);
+		ByteBuffer byteBuffer = Backend.getInstance().compat.mapBufferRange.mapBuffer(owner.type, offset, length, owner.flags);
+
+		GlError error = GlError.poll();
+
+		if (error != null) {
+			throw new GlException(error, StringUtil.args("mapBuffer", owner.type, offset, length, owner.flags));
+		}
 
 		setInternal(byteBuffer);
 	}
 
+	@Override
+	public MappedBuffer position(int p) {
+		if (p < offset || p >= offset + length) {
+			throw new IndexOutOfBoundsException("Index " + p + " is not mapped");
+		}
+		return super.position(p - (int) offset);
+	}
+
 	@Override
 	public void flush() {
 

src/main/java/com/jozufozu/flywheel/backend/gl/error/GlError.java

@@ -0,0 +1,38 @@
+package com.jozufozu.flywheel.backend.gl.error;
+
+import org.lwjgl.opengl.GL20;
+import org.lwjgl.opengl.GL30;
+
+import it.unimi.dsi.fastutil.ints.Int2ObjectArrayMap;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+
+public enum GlError {
+	INVALID_ENUM(GL20.GL_INVALID_ENUM),
+	INVALID_VALUE(GL20.GL_INVALID_VALUE),
+	INVALID_OPERATION(GL20.GL_INVALID_OPERATION),
+	INVALID_FRAMEBUFFER_OPERATION(GL30.GL_INVALID_FRAMEBUFFER_OPERATION),
+	OUT_OF_MEMORY(GL20.GL_OUT_OF_MEMORY),
+	STACK_UNDERFLOW(GL20.GL_STACK_UNDERFLOW),
+	STACK_OVERFLOW(GL20.GL_STACK_OVERFLOW),
+	;
+
+	private static final Int2ObjectMap<GlError> errorLookup = new Int2ObjectArrayMap<>();
+
+	static {
+		errorLookup.defaultReturnValue(null);
+		for (GlError value : values()) {
+			errorLookup.put(value.glEnum, value);
+		}
+	}
+
+	final int glEnum;
+
+	GlError(int glEnum) {
+		this.glEnum = glEnum;
+	}
+
+
+	public static GlError poll() {
+		return errorLookup.get(GL20.glGetError());
+	}
+}

src/main/java/com/jozufozu/flywheel/backend/gl/error/GlException.java

@@ -0,0 +1,38 @@
+package com.jozufozu.flywheel.backend.gl.error;
+
+public class GlException extends RuntimeException {
+
+	final GlError errorCode;
+
+	@Override
+	public String toString() {
+		String s = getClass().getName();
+		String message = getLocalizedMessage();
+		String withCode = s + ": " + errorCode;
+		return (message != null) ? (withCode + ": " + message) : withCode;
+	}
+
+	public GlException(GlError errorCode) {
+		this.errorCode = errorCode;
+	}
+
+	public GlException(GlError errorCode, String message) {
+		super(message);
+		this.errorCode = errorCode;
+	}
+
+	public GlException(GlError errorCode, String message, Throwable cause) {
+		super(message, cause);
+		this.errorCode = errorCode;
+	}
+
+	public GlException(GlError errorCode, Throwable cause) {
+		super(cause);
+		this.errorCode = errorCode;
+	}
+
+	public GlException(GlError errorCode, String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
+		super(message, cause, enableSuppression, writableStackTrace);
+		this.errorCode = errorCode;
+	}
+}

src/main/java/com/jozufozu/flywheel/backend/gl/versioned/BufferStorage.java

@@ -4,6 +4,8 @@ import org.lwjgl.opengl.ARBBufferStorage;
 import org.lwjgl.opengl.GL44;
 import org.lwjgl.opengl.GLCapabilities;
 
+import com.jozufozu.flywheel.backend.gl.buffer.GlBufferType;
+
 public enum BufferStorage implements GlVersioned {
 
 	GL44CORE {
@@ -13,8 +15,8 @@ public enum BufferStorage implements GlVersioned {
 		}
 
 		@Override
-		public void bufferStorage(int target, long size, int flags) {
+		public void bufferStorage(GlBufferType target, long size, int flags) {
-			GL44.glBufferStorage(target, size, flags);
+			GL44.glBufferStorage(target.glEnum, size, flags);
 		}
 	},
 	ARB {
@@ -24,8 +26,8 @@ public enum BufferStorage implements GlVersioned {
 		}
 
 		@Override
-		public void bufferStorage(int target, long size, int flags) {
+		public void bufferStorage(GlBufferType target, long size, int flags) {
-			ARBBufferStorage.glBufferStorage(target, size, flags);
+			ARBBufferStorage.glBufferStorage(target.glEnum, size, flags);
 		}
 	},
 	UNSUPPORTED {
@@ -35,10 +37,10 @@ public enum BufferStorage implements GlVersioned {
 		}
 
 		@Override
-		public void bufferStorage(int target, long size, int flags) {
+		public void bufferStorage(GlBufferType target, long size, int flags) {
 			throw new UnsupportedOperationException();
 		}
 	};
 
-	public abstract void bufferStorage(int target, long size, int flags);
+	public abstract void bufferStorage(GlBufferType target, long size, int flags);
 }

src/main/java/com/jozufozu/flywheel/backend/gl/versioned/GlCompat.java

@@ -12,6 +12,7 @@ import org.lwjgl.system.MemoryUtil;
 import com.jozufozu.flywheel.backend.gl.versioned.framebuffer.Blit;
 import com.jozufozu.flywheel.backend.gl.versioned.framebuffer.Framebuffer;
 import com.jozufozu.flywheel.backend.gl.versioned.instancing.DrawInstanced;
+import com.jozufozu.flywheel.backend.gl.versioned.instancing.BaseVertex;
 import com.jozufozu.flywheel.backend.gl.versioned.instancing.InstancedArrays;
 import com.jozufozu.flywheel.backend.gl.versioned.instancing.VertexArrayObject;
 
@@ -32,6 +33,7 @@ public class GlCompat {
 	public final BufferStorage bufferStorage;
 
 	public final RGPixelFormat pixelFormat;
+	public final BaseVertex baseVertex;
 
 	public GlCompat(GLCapabilities caps) {
 		mapBufferRange = getLatest(MapBufferRange.class, caps);
@@ -39,6 +41,7 @@ public class GlCompat {
 		vao = getLatest(VertexArrayObject.class, caps);
 		instancedArrays = getLatest(InstancedArrays.class, caps);
 		drawInstanced = getLatest(DrawInstanced.class, caps);
+		baseVertex = getLatest(BaseVertex.class, caps);
 		blit = getLatest(Blit.class, caps);
 		fbo = getLatest(Framebuffer.class, caps);
 		bufferStorage = getLatest(BufferStorage.class, caps);

src/main/java/com/jozufozu/flywheel/backend/gl/versioned/instancing/BaseVertex.java

@@ -0,0 +1,62 @@
+package com.jozufozu.flywheel.backend.gl.versioned.instancing;
+
+import org.lwjgl.opengl.ARBDrawElementsBaseVertex;
+import org.lwjgl.opengl.ARBDrawInstanced;
+import org.lwjgl.opengl.EXTDrawInstanced;
+import org.lwjgl.opengl.GL32;
+import org.lwjgl.opengl.GLCapabilities;
+
+import com.jozufozu.flywheel.backend.gl.GlNumericType;
+import com.jozufozu.flywheel.backend.gl.GlPrimitive;
+import com.jozufozu.flywheel.backend.gl.versioned.GlVersioned;
+
+public enum BaseVertex implements GlVersioned {
+	GL31_CORE {
+		@Override
+		public boolean supported(GLCapabilities caps) {
+			return caps.OpenGL31;
+		}
+
+		@Override
+		public void drawElementsInstancedBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int instanceCount, int baseVertex) {
+			GL32.glDrawElementsInstancedBaseVertex(mode.glEnum, elementCount, type.getGlEnum(), indices, instanceCount, baseVertex);
+		}
+
+		@Override
+		public void drawElementsBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int baseVertex) {
+			GL32.glDrawElementsBaseVertex(mode.glEnum, elementCount, type.getGlEnum(), indices, baseVertex);
+		}
+	},
+	ARB {
+		@Override
+		public boolean supported(GLCapabilities caps) {
+			return caps.GL_ARB_draw_elements_base_vertex;
+		}
+
+		@Override
+		public void drawElementsInstancedBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int instanceCount, int baseVertex) {
+			ARBDrawElementsBaseVertex.glDrawElementsInstancedBaseVertex(mode.glEnum, elementCount, type.getGlEnum(), indices, instanceCount, baseVertex);
+		}
+
+		@Override
+		public void drawElementsBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int baseVertex) {
+			ARBDrawElementsBaseVertex.glDrawElementsBaseVertex(mode.glEnum, elementCount, type.getGlEnum(), indices, baseVertex);
+		}
+	},
+	UNSUPPORTED {
+		@Override
+		public boolean supported(GLCapabilities caps) {
+			return true;
+		}
+	};
+
+
+	public void drawElementsInstancedBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int instanceCount, int baseVertex) {
+		throw new UnsupportedOperationException();
+	}
+
+
+	public void drawElementsBaseVertex(GlPrimitive mode, int elementCount, GlNumericType type, long indices, int baseVertex) {
+		throw new UnsupportedOperationException();
+	}
+}

src/main/java/com/jozufozu/flywheel/backend/gl/versioned/instancing/DrawInstanced.java

@@ -3,6 +3,7 @@ package com.jozufozu.flywheel.backend.gl.versioned.instancing;
 import org.lwjgl.opengl.ARBDrawInstanced;
 import org.lwjgl.opengl.EXTDrawInstanced;
 import org.lwjgl.opengl.GL31;
+import org.lwjgl.opengl.GL46;
 import org.lwjgl.opengl.GLCapabilities;
 
 import com.jozufozu.flywheel.backend.gl.GlNumericType;
@@ -10,7 +11,7 @@ import com.jozufozu.flywheel.backend.gl.GlPrimitive;
 import com.jozufozu.flywheel.backend.gl.versioned.GlVersioned;
 
 public enum DrawInstanced implements GlVersioned {
-	GL31_DRAW_INSTANCED {
+	GL31_CORE {
 		@Override
 		public boolean supported(GLCapabilities caps) {
 			return caps.OpenGL31;
@@ -26,7 +27,7 @@ public enum DrawInstanced implements GlVersioned {
 			GL31.glDrawElementsInstanced(mode.glEnum, elementCount, type.getGlEnum(), indices, primcount);
 		}
 	},
-	ARB_DRAW_INSTANCED {
+	ARB {
 		@Override
 		public boolean supported(GLCapabilities caps) {
 			return caps.GL_ARB_draw_instanced;
@@ -42,7 +43,7 @@ public enum DrawInstanced implements GlVersioned {
 			ARBDrawInstanced.glDrawElementsInstancedARB(mode.glEnum, elementCount, type.getGlEnum(), indices, primcount);
 		}
 	},
-	EXT_DRAW_INSTANCED {
+	EXT {
 		@Override
 		public boolean supported(GLCapabilities caps) {
 			return caps.GL_EXT_draw_instanced;

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

@@ -2,7 +2,6 @@ package com.jozufozu.flywheel.backend.instancing;
 
 import java.util.ArrayList;
 import java.util.BitSet;
-import java.util.function.Supplier;
 
 import com.jozufozu.flywheel.backend.Backend;
 import com.jozufozu.flywheel.backend.gl.GlVertexArray;
@@ -11,8 +10,8 @@ import com.jozufozu.flywheel.backend.gl.buffer.GlBuffer;
 import com.jozufozu.flywheel.backend.gl.buffer.GlBufferType;
 import com.jozufozu.flywheel.backend.gl.buffer.MappedBuffer;
 import com.jozufozu.flywheel.backend.material.MaterialSpec;
+import com.jozufozu.flywheel.backend.model.ModelPool;
 import com.jozufozu.flywheel.backend.model.IBufferedModel;
-import com.jozufozu.flywheel.backend.model.IndexedModel;
 import com.jozufozu.flywheel.core.model.IModel;
 import com.jozufozu.flywheel.util.AttribUtil;
 
@@ -36,25 +35,27 @@ import com.jozufozu.flywheel.util.AttribUtil;
  */
 public class Instancer<D extends InstanceData> {
 
-	protected final Supplier<IModel> gen;
+	private final ModelPool modelAllocator;
-	protected final VertexFormat instanceFormat;
+	private final IModel modelData;
-	protected final IInstanceFactory<D> factory;
+	private final VertexFormat instanceFormat;
+	private final IInstanceFactory<D> factory;
 
-	protected IBufferedModel model;
+	private IBufferedModel model;
-	protected GlVertexArray vao;
+	private GlVertexArray vao;
-	protected GlBuffer instanceVBO;
+	private GlBuffer instanceVBO;
-	protected int glBufferSize = -1;
+	private int glBufferSize = -1;
-	protected int glInstanceCount = 0;
+	private int glInstanceCount = 0;
 	private boolean deleted;
 	private boolean initialized;
 
-	protected final ArrayList<D> data = new ArrayList<>();
+	private final ArrayList<D> data = new ArrayList<>();
 
 	boolean anyToRemove;
 	boolean anyToUpdate;
 
-	public Instancer(Supplier<IModel> model, MaterialSpec<D> spec) {
+	public Instancer(ModelPool modelAllocator, IModel model, MaterialSpec<D> spec) {
-		this.gen = model;
+		this.modelAllocator = modelAllocator;
+		this.modelData = model;
 		this.factory = spec.getInstanceFactory();
 		this.instanceFormat = spec.getInstanceFormat();
 	}
@@ -80,7 +81,6 @@ public class Instancer<D extends InstanceData> {
 	}
 
 	public void render() {
-		if (!isInitialized()) init();
 		if (invalid()) return;
 
 		vao.bind();
@@ -98,28 +98,28 @@ public class Instancer<D extends InstanceData> {
 		return deleted || model == null;
 	}
 
-	private void init() {
+	public void init() {
+		if (isInitialized()) return;
+
 		initialized = true;
-		IModel iModel = gen.get();
 
-		if (iModel.empty()) {
-			return;
-		}
-
-		model = new IndexedModel(iModel);
 		vao = new GlVertexArray();
-		instanceVBO = GlBuffer.requestPersistent(GlBufferType.ARRAY_BUFFER);
+
+		model = modelAllocator.alloc(modelData)
+				.setReallocCallback(arenaModel -> {
+					vao.bind();
+
+					model.setupState();
+
+					vao.unbind();
+				});
 
 		vao.bind();
 
-		// bind the model's vbo to our vao
+		instanceVBO = GlBuffer.requestPersistent(GlBufferType.ARRAY_BUFFER);
-		model.setupState();
-
 		AttribUtil.enableArrays(model.getAttributeCount() + instanceFormat.getAttributeCount());
 
 		vao.unbind();
-
-		model.clearState();
 	}
 
 	public boolean isInitialized() {

src/main/java/com/jozufozu/flywheel/backend/material/InstanceMaterial.java

@@ -1,7 +1,6 @@
 package com.jozufozu.flywheel.backend.material;
 
 import java.util.concurrent.ExecutionException;
-import java.util.function.Consumer;
 import java.util.function.Supplier;
 
 import com.google.common.cache.Cache;
@@ -9,6 +8,7 @@ import com.google.common.cache.CacheBuilder;
 import com.jozufozu.flywheel.backend.RenderWork;
 import com.jozufozu.flywheel.backend.instancing.InstanceData;
 import com.jozufozu.flywheel.backend.instancing.Instancer;
+import com.jozufozu.flywheel.backend.model.ModelPool;
 import com.jozufozu.flywheel.core.PartialModel;
 import com.jozufozu.flywheel.core.model.BlockModel;
 import com.jozufozu.flywheel.core.model.IModel;
@@ -25,12 +25,14 @@ import net.minecraft.util.Direction;
  */
 public class InstanceMaterial<D extends InstanceData> {
 
+	final ModelPool modelPool;
 	protected final Cache<Object, Instancer<D>> models;
 	protected final MaterialSpec<D> spec;
 
 	public InstanceMaterial(MaterialSpec<D> spec) {
 		this.spec = spec;
 
+		modelPool = new ModelPool(spec.getModelFormat(), spec.getModelFormat().getStride() * 64);
 		this.models = CacheBuilder.newBuilder()
 				.removalListener(notification -> {
 					Instancer<?> instancer = (Instancer<?>) notification.getValue();
@@ -48,7 +50,7 @@ public class InstanceMaterial<D extends InstanceData> {
 	 */
 	public Instancer<D> model(Object key, Supplier<IModel> modelSupplier) {
 		try {
-			return models.get(key, () -> new Instancer<>(modelSupplier, spec));
+			return models.get(key, () -> new Instancer<>(modelPool, modelSupplier.get(), spec));
 		} catch (ExecutionException e) {
 			throw new RuntimeException("error creating instancer", e);
 		}
@@ -79,6 +81,7 @@ public class InstanceMaterial<D extends InstanceData> {
 
 	public void delete() {
 		models.invalidateAll();
+		modelPool.delete();
 	}
 
 	/**
@@ -90,11 +93,4 @@ public class InstanceMaterial<D extends InstanceData> {
 				.forEach(Instancer::clear);
 	}
 
-	public void forEachInstancer(Consumer<Instancer<D>> f) {
-		for (Instancer<D> model : models.asMap()
-				.values()) {
-			f.accept(model);
-		}
-	}
-
 }

src/main/java/com/jozufozu/flywheel/backend/material/MaterialManager.java

@@ -17,7 +17,6 @@ import com.jozufozu.flywheel.core.shader.WorldProgram;
 import com.jozufozu.flywheel.util.WeakHashSet;
 
 import net.minecraft.client.renderer.ActiveRenderInfo;
-import net.minecraft.client.renderer.RenderType;
 import net.minecraft.inventory.container.PlayerContainer;
 import net.minecraft.util.ResourceLocation;
 import net.minecraft.util.math.BlockPos;

src/main/java/com/jozufozu/flywheel/backend/material/MaterialRenderer.java

@@ -1,5 +1,6 @@
 package com.jozufozu.flywheel.backend.material;
 
+import java.util.Collection;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
@@ -24,6 +25,14 @@ public class MaterialRenderer<P extends WorldProgram> {
 	public void render(Matrix4f viewProjection, double camX, double camY, double camZ) {
 		if (material.nothingToRender()) return;
 
+		Collection<? extends Instancer<?>> instancers = material.models.asMap()
+				.values();
+
+		// initialize all uninitialized instancers...
+		instancers.forEach(Instancer::init);
+		// ...and then flush the model arena in case anything was marked for upload
+		material.modelPool.flush();
+
 		P program = this.program.get();
 
 		program.bind();
@@ -32,7 +41,7 @@ public class MaterialRenderer<P extends WorldProgram> {
 
 		setupFunc.accept(program);
 
-		material.forEachInstancer(Instancer::render);
+		instancers.forEach(Instancer::render);
 	}
 
 }

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

@@ -2,6 +2,8 @@ package com.jozufozu.flywheel.backend.model;
 
 import static org.lwjgl.opengl.GL20.glDrawArrays;
 
+import org.lwjgl.opengl.GL44;
+
 import com.jozufozu.flywheel.backend.Backend;
 import com.jozufozu.flywheel.backend.gl.GlPrimitive;
 import com.jozufozu.flywheel.backend.gl.attrib.VertexFormat;
@@ -37,6 +39,10 @@ public class BufferedModel implements IBufferedModel {
 		vbo.unbind();
 	}
 
+	public boolean isDeleted() {
+		return deleted;
+	}
+
 	public VertexFormat getFormat() {
 		return model.format();
 	}
@@ -45,10 +51,6 @@ public class BufferedModel implements IBufferedModel {
 		return model.vertexCount();
 	}
 
-	public boolean valid() {
-		return getVertexCount() > 0 && !deleted;
-	}
-
 	/**
 	 * The VBO/VAO should be bound externally.
 	 */

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

@@ -8,8 +8,6 @@ public interface IBufferedModel {
 
 	int getVertexCount();
 
-	boolean valid();
-
 	/**
 	 * The VBO/VAO should be bound externally.
 	 */
@@ -24,8 +22,14 @@ public interface IBufferedModel {
 	 */
 	void drawInstances(int instanceCount);
 
+	boolean isDeleted();
+
 	void delete();
 
+	default boolean valid() {
+		return getVertexCount() > 0 && !isDeleted();
+	}
+
 	default int getAttributeCount() {
 		return getFormat().getAttributeCount();
 	}

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

@@ -0,0 +1,229 @@
+package com.jozufozu.flywheel.backend.model;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.jozufozu.flywheel.backend.Backend;
+import com.jozufozu.flywheel.backend.gl.GlPrimitive;
+import com.jozufozu.flywheel.backend.gl.attrib.VertexFormat;
+import com.jozufozu.flywheel.backend.gl.buffer.GlBuffer;
+import com.jozufozu.flywheel.backend.gl.buffer.GlBufferType;
+import com.jozufozu.flywheel.backend.gl.buffer.MappedBuffer;
+import com.jozufozu.flywheel.backend.gl.buffer.MappedGlBuffer;
+import com.jozufozu.flywheel.core.model.IModel;
+import com.jozufozu.flywheel.util.AttribUtil;
+import com.jozufozu.flywheel.util.StringUtil;
+
+public class ModelPool {
+
+	protected final VertexFormat format;
+
+	private final List<PooledModel> models = new ArrayList<>();
+
+	private final List<PooledModel> pendingUpload = new ArrayList<>();
+
+	private final GlBuffer vbo;
+	private int bufferSize;
+
+	private int vertices;
+
+	private boolean dirty;
+	private boolean anyToRemove;
+
+	public ModelPool(VertexFormat format, int initialSize) {
+		this.format = format;
+		bufferSize = initialSize;
+
+		vbo = new MappedGlBuffer(GlBufferType.ARRAY_BUFFER);
+
+		vbo.bind();
+		vbo.alloc(bufferSize);
+		vbo.unbind();
+	}
+
+	/**
+	 * Allocate a model in the arena.
+	 *
+	 * @param model The model to allocate.
+	 * @return A handle to the allocated model.
+	 */
+	public PooledModel alloc(IModel model) {
+		PooledModel bufferedModel = new PooledModel(model, vertices);
+		vertices += model.vertexCount();
+		models.add(bufferedModel);
+		pendingUpload.add(bufferedModel);
+
+		setDirty();
+		return bufferedModel;
+	}
+
+	public void flush() {
+		if (dirty) {
+			if (anyToRemove) processDeletions();
+
+			vbo.bind();
+			if (realloc()) {
+				uploadAll();
+			} else {
+				uploadPending();
+			}
+			vbo.unbind();
+
+			dirty = false;
+			pendingUpload.clear();
+		}
+	}
+
+	private void processDeletions() {
+
+		// remove deleted models
+		models.removeIf(PooledModel::isDeleted);
+
+		// re-evaluate first vertex for each model
+		int vertices = 0;
+		for (PooledModel model : models) {
+			if (model.first != vertices)
+				pendingUpload.add(model);
+
+			model.first = vertices;
+
+			vertices += model.getVertexCount();
+		}
+
+		this.vertices = vertices;
+		this.anyToRemove = false;
+	}
+
+	/**
+	 * Assumes vbo is bound.
+	 *
+	 * @return true if the buffer was reallocated
+	 */
+	private boolean realloc() {
+		int neededSize = vertices * format.getStride();
+		if (neededSize > bufferSize) {
+			bufferSize = neededSize + 128;
+			vbo.alloc(bufferSize);
+
+			return true;
+		}
+
+		return false;
+	}
+
+	private void uploadAll() {
+		MappedBuffer buffer = vbo.getBuffer(0, bufferSize);
+
+		for (PooledModel model : models) {
+			model.model.buffer(buffer);
+			if (model.callback != null)
+				model.callback.invoke(model);
+		}
+
+		buffer.flush();
+	}
+
+	private void uploadPending() {
+		MappedBuffer buffer = vbo.getBuffer(0, bufferSize);
+
+		int stride = format.getStride();
+		for (PooledModel model : pendingUpload) {
+			int pos = model.first * stride;
+			buffer.position(pos);
+			model.model.buffer(buffer);
+			if (model.callback != null)
+				model.callback.invoke(model);
+		}
+		pendingUpload.clear();
+
+		buffer.flush();
+	}
+
+	private void setDirty() {
+		dirty = true;
+	}
+
+	public void delete() {
+		vbo.delete();
+	}
+
+	public class PooledModel implements IBufferedModel {
+
+		private final ElementBuffer ebo;
+		private Callback callback;
+
+		private final IModel model;
+		private int first;
+
+		private boolean remove;
+
+		public PooledModel(IModel model, int first) {
+			this.model = model;
+			this.first = first;
+			ebo = model.createEBO();
+		}
+
+		@Override
+		public VertexFormat getFormat() {
+			return model.format();
+		}
+
+		@Override
+		public int getVertexCount() {
+			return model.vertexCount();
+		}
+
+		@Override
+		public void setupState() {
+			vbo.bind();
+			ebo.bind();
+			AttribUtil.enableArrays(getAttributeCount());
+			getFormat().vertexAttribPointers(0);
+		}
+
+		@Override
+		public void clearState() {
+			AttribUtil.disableArrays(getAttributeCount());
+			ebo.unbind();
+			vbo.unbind();
+		}
+
+		@Override
+		public void drawCall() {
+			Backend.getInstance().compat.baseVertex.drawElementsBaseVertex(GlPrimitive.TRIANGLES, ebo.elementCount, ebo.eboIndexType, 0, first);
+		}
+
+		@Override
+		public void drawInstances(int instanceCount) {
+			if (!valid()) return;
+
+			ebo.bind();
+
+			Backend.log.info(StringUtil.args("drawElementsInstancedBaseVertex", GlPrimitive.TRIANGLES, ebo.elementCount, ebo.eboIndexType, 0, instanceCount, first));
+
+			Backend.getInstance().compat.baseVertex.drawElementsInstancedBaseVertex(GlPrimitive.TRIANGLES, ebo.elementCount, ebo.eboIndexType, 0, instanceCount, first);
+		}
+
+		@Override
+		public boolean isDeleted() {
+			return false;
+		}
+
+		@Override
+		public void delete() {
+			setDirty();
+			anyToRemove = true;
+			remove = true;
+		}
+
+		public PooledModel setReallocCallback(Callback callback) {
+			this.callback = callback;
+			return this;
+		}
+	}
+
+	@FunctionalInterface
+	public interface Callback {
+		void invoke(PooledModel arenaModel);
+	}
+}

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

@@ -30,14 +30,14 @@ import net.minecraftforge.fml.common.Mod;
 @Mod.EventBusSubscriber(Dist.CLIENT)
 public class QuadConverter {
 
-	public static final int STARTING_CAPACITY = 42;
+	public static final int STARTING_CAPACITY = 42; // 255 / 6 = 42
 
 	private static QuadConverter INSTANCE;
 
 	@Nonnull
 	public static QuadConverter getInstance() {
 		if (INSTANCE == null) {
-			INSTANCE = new QuadConverter(STARTING_CAPACITY); // 255 / 6 = 42
+			INSTANCE = new QuadConverter(STARTING_CAPACITY);
 		}
 
 		return INSTANCE;
@@ -157,14 +157,14 @@ public class QuadConverter {
 	 * </pre>
 	 */
 	private static GlNumericType getSmallestIndexType(int indexCount) {
-		indexCount = indexCount >>> 8;
+//		indexCount = indexCount >>> 8;
-		if (indexCount == 0) {
+//		if (indexCount == 0) {
-			return GlNumericType.UBYTE;
+//			return GlNumericType.UBYTE;
-		}
+//		}
-		indexCount = indexCount >>> 8;
+//		indexCount = indexCount >>> 8;
-		if (indexCount == 0) {
+//		if (indexCount == 0) {
-			return GlNumericType.USHORT;
+//			return GlNumericType.USHORT;
-		}
+//		}
 
 		return GlNumericType.UINT;
 	}

src/main/java/com/jozufozu/flywheel/util/StringUtil.java

@@ -1,6 +1,17 @@
 package com.jozufozu.flywheel.util;
 
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
 public class StringUtil {
+
+	public static String args(String functionName, Object... args) {
+
+		return functionName + '(' + Arrays.stream(args)
+				.map(Object::toString)
+				.collect(Collectors.joining(", ")) + ')';
+	}
+
 	public static String trimEnd(String value) {
 		int len = value.length();
 		int st = 0;