The version vision

- Implement rudimentary backend version requirements
- Backends ship with a hard coded backend version
- Mods can specify a minimum major/minor backend version
- If a backend's version is below any mod's required version it is
  considered disabled

common/src/api/java/dev/engine_room/flywheel/api/backend/Backend.java

@@ -13,6 +13,13 @@ public interface Backend {
 	 */
 	Engine createEngine(LevelAccessor level);
 
+	/**
+	 * The version of flywheel this backend was written against.
+	 *
+	 * @return A backend version.
+	 */
+	BackendVersion version();
+
 	/**
 	 * The priority of this backend.
 	 * <p>The backend with the highest priority upon first launch will be chosen as the default backend.

common/src/api/java/dev/engine_room/flywheel/api/backend/BackendVersion.java

@@ -0,0 +1,11 @@
+package dev.engine_room.flywheel.api.backend;
+
+public record BackendVersion(int major, int minor) implements Comparable<BackendVersion> {
+	@Override
+	public int compareTo(BackendVersion o) {
+		if (major != o.major) {
+			return Integer.compare(major, o.major);
+		}
+		return Integer.compare(minor, o.minor);
+	}
+}

common/src/backend/java/dev/engine_room/flywheel/backend/Backends.java

@@ -2,6 +2,7 @@
 
 import dev.engine_room.flywheel.api.Flywheel;
 import dev.engine_room.flywheel.api.backend.Backend;
+import dev.engine_room.flywheel.api.backend.BackendVersion;
 import dev.engine_room.flywheel.backend.compile.IndirectPrograms;
 import dev.engine_room.flywheel.backend.compile.InstancingPrograms;
 import dev.engine_room.flywheel.backend.engine.EngineImpl;
@@ -12,11 +13,14 @@
 import dev.engine_room.flywheel.lib.util.ShadersModHelper;
 
 public final class Backends {
+	private static final BackendVersion VERSION = new BackendVersion(1, 0);
+
 	/**
 	 * Use GPU instancing to render everything.
 	 */
 	public static final Backend INSTANCING = SimpleBackend.builder()
 			.engineFactory(level -> new EngineImpl(level, new InstancedDrawManager(InstancingPrograms.get()), 256))
+			.version(VERSION)
 			.priority(500)
 			.supported(() -> GlCompat.SUPPORTS_INSTANCING && InstancingPrograms.allLoaded() && !ShadersModHelper.isShaderPackInUse())
 			.register(Flywheel.rl("instancing"));
@@ -26,6 +30,7 @@ public final class Backends {
 	 */
 	public static final Backend INDIRECT = SimpleBackend.builder()
 			.engineFactory(level -> new EngineImpl(level, new IndirectDrawManager(IndirectPrograms.get()), 256))
+			.version(VERSION)
 			.priority(1000)
 			.supported(() -> GlCompat.SUPPORTS_INDIRECT && IndirectPrograms.allLoaded() && !ShadersModHelper.isShaderPackInUse())
 			.register(Flywheel.rl("indirect"));

common/src/lib/java/dev/engine_room/flywheel/lib/backend/SimpleBackend.java

@@ -4,7 +4,10 @@
 import java.util.function.BooleanSupplier;
 import java.util.function.Function;
 
+import org.jetbrains.annotations.Nullable;
+
 import dev.engine_room.flywheel.api.backend.Backend;
+import dev.engine_room.flywheel.api.backend.BackendVersion;
 import dev.engine_room.flywheel.api.backend.Engine;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.level.LevelAccessor;
@@ -13,11 +16,13 @@ public final class SimpleBackend implements Backend {
 	private final Function<LevelAccessor, Engine> engineFactory;
 	private final int priority;
 	private final BooleanSupplier isSupported;
+	private final BackendVersion version;
 
-	public SimpleBackend(int priority, Function<LevelAccessor, Engine> engineFactory, BooleanSupplier isSupported) {
+	public SimpleBackend(int priority, Function<LevelAccessor, Engine> engineFactory, BooleanSupplier isSupported, BackendVersion version) {
 		this.priority = priority;
 		this.engineFactory = engineFactory;
 		this.isSupported = isSupported;
+		this.version = version;
 	}
 
 	public static Builder builder() {
@@ -29,6 +34,11 @@ public Engine createEngine(LevelAccessor level) {
 		return engineFactory.apply(level);
 	}
 
+	@Override
+	public BackendVersion version() {
+		return version;
+	}
+
 	@Override
 	public int priority() {
 		return priority;
@@ -40,9 +50,13 @@ public boolean isSupported() {
 	}
 
 	public static final class Builder {
-		private Function<LevelAccessor, Engine> engineFactory;
 		private int priority = 0;
+		@Nullable
+		private Function<LevelAccessor, Engine> engineFactory;
+		@Nullable
 		private BooleanSupplier isSupported;
+		@Nullable
+		private BackendVersion version;
 
 		public Builder engineFactory(Function<LevelAccessor, Engine> engineFactory) {
 			this.engineFactory = engineFactory;
@@ -59,11 +73,17 @@ public Builder supported(BooleanSupplier isSupported) {
 			return this;
 		}
 
+		public Builder version(BackendVersion version) {
+			this.version = version;
+			return this;
+		}
+
 		public Backend register(ResourceLocation id) {
 			Objects.requireNonNull(engineFactory);
 			Objects.requireNonNull(isSupported);
+			Objects.requireNonNull(version);
 
-			return Backend.REGISTRY.registerAndGet(id, new SimpleBackend(priority, engineFactory, isSupported));
+			return Backend.REGISTRY.registerAndGet(id, new SimpleBackend(priority, engineFactory, isSupported, version));
 		}
 	}
 }

common/src/main/java/dev/engine_room/flywheel/impl/BackendManagerImpl.java

@@ -1,9 +1,11 @@
 package dev.engine_room.flywheel.impl;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import dev.engine_room.flywheel.api.Flywheel;
 import dev.engine_room.flywheel.api.backend.Backend;
+import dev.engine_room.flywheel.api.backend.BackendVersion;
 import dev.engine_room.flywheel.impl.visualization.VisualizationManagerImpl;
 import dev.engine_room.flywheel.lib.backend.SimpleBackend;
 import net.minecraft.client.multiplayer.ClientLevel;
@@ -15,6 +17,7 @@ public final class BackendManagerImpl {
 				throw new UnsupportedOperationException("Cannot create engine when backend is off.");
 			})
 			.supported(() -> true)
+			.version(new BackendVersion(0, 0))
 			.register(Flywheel.rl("off"));
 
 	public static final Backend DEFAULT_BACKEND = findDefaultBackend();
@@ -33,7 +36,7 @@ public static boolean isBackendOn() {
 	}
 
 	// Don't store this statically because backends can theoretically change their priorities at runtime.
-	private static ArrayList<Backend> backendsByPriority() {
+	private static List<Backend> backendsByPriority() {
 		var backends = new ArrayList<>(Backend.REGISTRY.getAll());
 
 		// Sort with keys backwards so that the highest priority is first.
@@ -53,27 +56,46 @@ private static Backend findDefaultBackend() {
 	}
 
 	private static void chooseBackend() {
+		var requirements = FlwImplXplat.INSTANCE.modRequirements();
+
 		var preferred = FlwConfig.INSTANCE.backend();
 		if (preferred.isSupported()) {
-			backend = preferred;
-			return;
+			if (meetsModRequirements(requirements, preferred)) {
+				backend = preferred;
+				return;
+			} else {
+				var minVersion = requirements.minimumBackendVersion();
+				FlwImpl.LOGGER.warn("Preferred backend '{}' does not meet minimum version requirement {}.{}", Backend.REGISTRY.getIdOrThrow(preferred), minVersion.major(), minVersion.minor());
+			}
 		}
 
+		backend = fallback(preferred, requirements);
+
+		FlwImpl.LOGGER.warn("Flywheel backend fell back from '{}' to '{}'", Backend.REGISTRY.getIdOrThrow(preferred), Backend.REGISTRY.getIdOrThrow(backend));
+	}
+
+	private static Backend fallback(Backend preferred, ModRequirements requirements) {
 		var backendsByPriority = backendsByPriority();
 
 		var startIndex = backendsByPriority.indexOf(preferred) + 1;
 
 		// For safety in case we don't find anything
-		backend = OFF_BACKEND;
+		var out = OFF_BACKEND;
 		for (int i = startIndex; i < backendsByPriority.size(); i++) {
 			var candidate = backendsByPriority.get(i);
 			if (candidate.isSupported()) {
-				backend = candidate;
-				break;
+				if (meetsModRequirements(requirements, candidate)) {
+					out = candidate;
+					break;
+				}
 			}
 		}
+		return out;
+	}
 
-		FlwImpl.LOGGER.warn("Flywheel backend fell back from '{}' to '{}'", Backend.REGISTRY.getIdOrThrow(preferred), Backend.REGISTRY.getIdOrThrow(backend));
+	private static boolean meetsModRequirements(ModRequirements requirements, Backend candidate) {
+		return candidate.version()
+				.compareTo(requirements.minimumBackendVersion()) >= 0;
 	}
 
 	public static String getBackendString() {

common/src/main/java/dev/engine_room/flywheel/impl/FlwImplXplat.java

@@ -17,4 +17,6 @@ public interface FlwImplXplat {
 	boolean useSodium0_6Compat();
 
 	boolean useIrisCompat();
+
+	ModRequirements modRequirements();
 }

common/src/main/java/dev/engine_room/flywheel/impl/ModRequirements.java

@@ -0,0 +1,10 @@
+package dev.engine_room.flywheel.impl;
+
+import java.util.List;
+
+import dev.engine_room.flywheel.api.backend.BackendVersion;
+
+public record ModRequirements(BackendVersion minimumBackendVersion, List<Entry> entries) {
+	public record Entry(String modId, BackendVersion version) {
+	}
+}

fabric/src/main/java/dev/engine_room/flywheel/impl/FlwImplXplatImpl.java

@@ -1,9 +1,17 @@
 package dev.engine_room.flywheel.impl;
 
+import java.util.ArrayList;
+import java.util.List;
+
+import org.jetbrains.annotations.Nullable;
+
+import dev.engine_room.flywheel.api.backend.BackendVersion;
 import dev.engine_room.flywheel.api.event.ReloadLevelRendererCallback;
 import dev.engine_room.flywheel.impl.compat.CompatMod;
 import dev.engine_room.flywheel.impl.compat.FabricSodiumCompat;
 import net.fabricmc.loader.api.FabricLoader;
+import net.fabricmc.loader.api.ModContainer;
+import net.fabricmc.loader.api.metadata.CustomValue;
 import net.minecraft.client.multiplayer.ClientLevel;
 
 public class FlwImplXplatImpl implements FlwImplXplat {
@@ -36,4 +44,54 @@ public boolean useSodium0_6Compat() {
 	public boolean useIrisCompat() {
 		return CompatMod.IRIS.isLoaded;
 	}
+
+	@Override
+	public ModRequirements modRequirements() {
+		List<ModRequirements.Entry> entries = new ArrayList<>();
+
+		for (ModContainer mod : FabricLoader.getInstance()
+				.getAllMods()) {
+			var metadata = mod.getMetadata();
+
+			var custom = metadata.getCustomValue("flywheel");
+
+			if (custom != null && custom.getType() == CustomValue.CvType.OBJECT) {
+				var object = custom.getAsObject();
+
+				var major = getCustomValueAsInt(object.get("backend_major_version"));
+				var minor = getCustomValueAsInt(object.get("backend_minor_version"));
+
+				// Major version is required
+				if (major != null) {
+					// Minor version defaults to 0
+					var version = new BackendVersion(major, minor == null ? 0 : minor);
+
+					entries.add(new ModRequirements.Entry(metadata.getId(), version));
+				} else {
+					FlwImpl.LOGGER.warn("Mod {} has invalid required backend version", metadata.getId());
+				}
+			}
+		}
+
+		if (!entries.isEmpty()) {
+			var minVersion = entries.stream()
+					.map(ModRequirements.Entry::version)
+					.min(BackendVersion::compareTo)
+					.get();
+
+			return new ModRequirements(minVersion, entries);
+		} else {
+			return new ModRequirements(new BackendVersion(0, 0), List.of());
+		}
+	}
+
+	@Nullable
+	private static Integer getCustomValueAsInt(@Nullable CustomValue major) {
+		if (major != null && major.getType() == CustomValue.CvType.NUMBER) {
+			return major.getAsNumber()
+					.intValue();
+		}
+
+		return null;
+	}
 }

fabric/src/main/resources/fabric.mod.json

@@ -35,5 +35,11 @@
   "breaks": {
     "sodium": ["<0.5.0", "~0.6.0- <0.6.0-beta.2"],
     "embeddium": "*"
+  },
+  "custom" : {
+    "flywheel" : {
+      "backend_major_version" : 1,
+      "backend_minor_version" : 0
+    }
   }
 }

forge/src/main/java/dev/engine_room/flywheel/impl/FlwImplXplatImpl.java

@@ -1,10 +1,18 @@
 package dev.engine_room.flywheel.impl;
 
+import java.util.ArrayList;
+import java.util.List;
+
+import com.electronwill.nightconfig.core.Config;
+
+import dev.engine_room.flywheel.api.backend.BackendVersion;
 import dev.engine_room.flywheel.api.event.ReloadLevelRendererEvent;
 import dev.engine_room.flywheel.impl.compat.CompatMod;
 import net.minecraft.client.multiplayer.ClientLevel;
 import net.minecraftforge.common.MinecraftForge;
+import net.minecraftforge.fml.ModList;
 import net.minecraftforge.fml.loading.LoadingModList;
+import net.minecraftforge.forgespi.language.IModInfo;
 
 public class FlwImplXplatImpl implements FlwImplXplat {
 	@Override
@@ -36,4 +44,46 @@ public boolean useSodium0_6Compat() {
 	public boolean useIrisCompat() {
 		return CompatMod.IRIS.isLoaded || CompatMod.OCULUS.isLoaded;
 	}
+
+	@Override
+	public ModRequirements modRequirements() {
+		List<ModRequirements.Entry> entries = new ArrayList<>();
+
+		ModList.get()
+				.forEachModFile(file -> {
+					var info = file.getModFileInfo();
+
+					for (IModInfo mod : info.getMods()) {
+						var modProperties = mod.getModProperties()
+								.get("flywheel");
+
+						// There's no well-defined API for custom properties like in fabric.
+						// It just returns an object, but internally it's represented with nightconfig.
+						if (modProperties instanceof Config config) {
+							// Minor version defaults to 0, major is required
+							int major = config.getIntOrElse("backend_major_version", Integer.MIN_VALUE);
+							int minor = config.getIntOrElse("backend_minor_version", 0);
+
+							if (major != Integer.MIN_VALUE) {
+								entries.add(new ModRequirements.Entry(mod.getModId(), new BackendVersion(major, minor)));
+							} else {
+								FlwImpl.LOGGER.warn("Mod {} has invalid required backend version", mod.getModId());
+							}
+						} else {
+							FlwImpl.LOGGER.warn("Mod {} has invalid flywheel properties", mod.getModId());
+						}
+					}
+				});
+
+		if (!entries.isEmpty()) {
+			var minVersion = entries.stream()
+					.map(ModRequirements.Entry::version)
+					.min(BackendVersion::compareTo)
+					.get();
+
+			return new ModRequirements(minVersion, entries);
+		} else {
+			return new ModRequirements(new BackendVersion(0, 0), List.of());
+		}
+	}
 }

forge/src/main/resources/META-INF/mods.toml

@@ -14,6 +14,10 @@ authors = "Jozufozu, PepperCode1"
 displayURL = "${mod_homepage}"
 displayTest = "IGNORE_ALL_VERSION"
 
+[modproperties.${ mod_id }.flywheel]
+backend_major_version = 1
+backend_minor_version = 0
+
 [[dependencies.${mod_id}]]
 modId = "minecraft"
 mandatory = true