Execute world-aware placement modifiers

tools/VanillaPlacementVectors.java

@@ -0,0 +1,47 @@
+import java.util.List;
+import java.util.stream.Stream;
+
+import net.minecraft.SharedConstants;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.Bootstrap;
+import net.minecraft.util.RandomSource;
+import net.minecraft.util.valueproviders.ClampedNormalInt;
+import net.minecraft.util.valueproviders.TrapezoidInt;
+import net.minecraft.world.level.levelgen.LegacyRandomSource;
+import net.minecraft.world.level.levelgen.placement.CountPlacement;
+import net.minecraft.world.level.levelgen.placement.PlacementModifier;
+import net.minecraft.world.level.levelgen.placement.RandomOffsetPlacement;
+
+// Emits placement stream vectors from the official 26.1.2 runtime. These
+// modifiers do not read PlacementContext, so no world or registry is required.
+public final class VanillaPlacementVectors {
+    public static void main(String[] args) {
+        SharedConstants.tryDetectVersion();
+        Bootstrap.bootStrap();
+
+        RandomSource offsetRandom = new LegacyRandomSource(12345L);
+        List<PlacementModifier> modifiers = List.of(
+                CountPlacement.of(3),
+                RandomOffsetPlacement.of(
+                        TrapezoidInt.of(-4, 4, 0),
+                        TrapezoidInt.of(-2, 2, 0)));
+        Stream<BlockPos> positions = Stream.of(new BlockPos(32, 10, -16));
+        for (PlacementModifier modifier : modifiers) {
+            positions = positions.flatMap(position -> modifier.getPositions(null, offsetRandom, position));
+        }
+        System.out.println("offset=" + positions.map(VanillaPlacementVectors::position).toList());
+
+        RandomSource normalRandom = new LegacyRandomSource(12345L);
+        ClampedNormalInt normal = ClampedNormalInt.of(0.0F, 3.0F, -10, 10);
+        StringBuilder samples = new StringBuilder();
+        for (int i = 0; i < 8; i++) {
+            if (i > 0) samples.append(',');
+            samples.append(normal.sample(normalRandom));
+        }
+        System.out.println("normal=" + samples);
+    }
+
+    private static String position(BlockPos position) {
+        return position.getX() + ":" + position.getY() + ":" + position.getZ();
+    }
+}