Add RegisterRenderBuffersEvent to register fixed BufferBuilders for R…

…enderTypes (#546)

patches/net/minecraft/client/renderer/RenderBuffers.java.patch

@@ -0,0 +1,10 @@
+--- a/net/minecraft/client/renderer/RenderBuffers.java
++++ b/net/minecraft/client/renderer/RenderBuffers.java
+@@ -39,6 +_,7 @@
+             put(p_307112_, RenderType.waterMask());
+             ModelBakery.DESTROY_TYPES.forEach(p_173062_ -> put(p_307112_, p_173062_));
+         });
++        net.neoforged.fml.ModLoader.get().postEvent(new net.neoforged.neoforge.client.event.RegisterRenderBuffersEvent(sortedmap));
+         this.crumblingBufferSource = MultiBufferSource.immediate(new BufferBuilder(1536));
+         this.bufferSource = MultiBufferSource.immediateWithBuffers(sortedmap, new BufferBuilder(786432));
+         this.outlineBufferSource = new OutlineBufferSource(this.bufferSource);

src/main/java/net/neoforged/neoforge/client/event/RegisterRenderBuffersEvent.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.client.event;
+
+import com.mojang.blaze3d.vertex.BufferBuilder;
+import java.util.SortedMap;
+import net.minecraft.client.renderer.RenderType;
+import net.neoforged.bus.api.Event;
+import net.neoforged.bus.api.ICancellableEvent;
+import net.neoforged.fml.LogicalSide;
+import net.neoforged.fml.event.IModBusEvent;
+import org.jetbrains.annotations.ApiStatus;
+
+/**
+ * Fired to allow mods to register custom {@linkplain BufferBuilder render buffers}.
+ * This allows to have dedicated {@linkplain BufferBuilder render buffer} for each {@linkplain RenderType render type}
+ * that can filled and rendered in batch
+ * This event is fired after the default Minecraft render buffers have been registered.
+ *
+ * <p>This event is not {@linkplain ICancellableEvent cancellable}, and does not {@linkplain HasResult have a result}.</p>
+ *
+ * <p>This event is fired on the mod-specific event bus, only on the {@linkplain LogicalSide#CLIENT logical client}.</p>
+ */
+public class RegisterRenderBuffersEvent extends Event implements IModBusEvent {
+    private final SortedMap<RenderType, BufferBuilder> renderBuffers;
+
+    @ApiStatus.Internal
+    public RegisterRenderBuffersEvent(SortedMap<RenderType, BufferBuilder> renderBuffers) {
+        this.renderBuffers = renderBuffers;
+    }
+
+    /**
+     * Registers a default render buffer with buffer size specified in the render type.
+     *
+     * @param renderType a render type of the render buffer
+     */
+    public void registerRenderBuffer(RenderType renderType) {
+        registerRenderBuffer(renderType, new BufferBuilder(renderType.bufferSize()));
+    }
+
+    /**
+     * Registers a render buffer for specified render type.
+     *
+     * @param renderType   a render type of the render buffer
+     * @param renderBuffer a render buffer to register
+     */
+    public void registerRenderBuffer(RenderType renderType, BufferBuilder renderBuffer) {
+        if (renderBuffers.containsKey(renderType)) {
+            throw new IllegalStateException("Duplicate attempt to register render buffer: " + renderType);
+        }
+
+        renderBuffers.put(renderType, renderBuffer);
+    }
+}

tests/src/main/java/net/neoforged/neoforge/debug/client/ClientEventTests.java

@@ -5,11 +5,16 @@
 
 package net.neoforged.neoforge.debug.client;
 
+import com.mojang.blaze3d.vertex.BufferBuilder;
+import java.util.Map;
 import net.minecraft.client.Minecraft;
+import net.minecraft.client.renderer.RenderType;
 import net.minecraft.network.chat.Component;
 import net.neoforged.api.distmarker.Dist;
 import net.neoforged.neoforge.client.event.ClientChatEvent;
 import net.neoforged.neoforge.client.event.ClientPlayerChangeGameTypeEvent;
+import net.neoforged.neoforge.client.event.RegisterRenderBuffersEvent;
+import net.neoforged.neoforge.client.event.RenderLevelStageEvent;
 import net.neoforged.testframework.DynamicTest;
 import net.neoforged.testframework.annotation.ForEachTest;
 import net.neoforged.testframework.annotation.TestHolder;
@@ -31,4 +36,29 @@ static void playerClientChatEvent(final ClientChatEvent event, final DynamicTest
     static void clientPlayerChangeGameTypeEvent(final ClientPlayerChangeGameTypeEvent event, final DynamicTest test) {
         test.requestConfirmation(Minecraft.getInstance().player, Component.literal("Did you just change your game mode from " + event.getCurrentGameType() + " to " + event.getNewGameType() + "?"));
     }
+
+    @TestHolder(description = { "Tests if the RegisterRenderBuffersEvent event is fired and whether the registered render buffer is represented within a fixed render buffer map" }, enabledByDefault = true)
+    static void registerRenderBuffersEvent(final DynamicTest test) {
+        test.framework().modEventBus().addListener((final RegisterRenderBuffersEvent event) -> {
+            event.registerRenderBuffer(RenderType.lightning());
+        });
+        test.framework().modEventBus().addListener((final RenderLevelStageEvent.RegisterStageEvent event) -> {
+            try {
+                var bufferSource = Minecraft.getInstance().renderBuffers().bufferSource();
+                var field = bufferSource.getClass().getDeclaredField("fixedBuffers");
+
+                field.setAccessible(true);
+
+                var fixedBuffers = (Map<RenderType, BufferBuilder>) field.get(bufferSource);
+
+                if (fixedBuffers != null && fixedBuffers.containsKey(RenderType.lightning())) {
+                    test.pass();
+                } else {
+                    test.fail("The render buffer for the specified render type was not registered");
+                }
+            } catch (Exception e) {
+                test.fail("Failed to access fixed buffers map");
+            }
+        });
+    }
 }