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stubbed out the carpet and lily pad collision fixes for Mojang 1.20.5… #99

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stubbed out the carpet and lily pad collision fixes for Mojang 1.20.5… #99

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814df3d
stubbed out the carpet and lily pad collision fixes for Mojang 1.20.5…
Wolf1098 Jul 11, 2026
ff8e2b0
Fix lillypad
Wolf1098 Jul 11, 2026
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132 changes: 93 additions & 39 deletions src/main/java/com/viaversion/viarewind/legacysupport/feature/BlockCollisionChanges.java
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Original file line number Diff line number Diff line change
Expand Up @@ -34,19 +34,70 @@
import static com.viaversion.viarewind.legacysupport.util.ReflectionUtil.getFieldAccessible;

public class BlockCollisionChanges {

public static void fixLilyPad(final Logger logger, final ProtocolVersion serverVersion) {
try {
// Modern Mojang runtime (1.20.5+ including 26.x)
if (serverVersion.newerThanOrEqualTo(ProtocolVersion.v1_20_5)) {
// Try both names depending on version
Class<?> lilyClass;
try {
lilyClass = Class.forName("net.minecraft.world.level.block.WaterlilyBlock");
} catch (ClassNotFoundException ex) {
lilyClass = Class.forName("net.minecraft.world.level.block.LilyPadBlock");
}

// Build replacement VoxelShape (old-style lily pad box)
Class<?> shapesClass = Class.forName("net.minecraft.world.phys.shapes.Shapes");
Method boxMethod = shapesClass.getMethod(
"box",
double.class, double.class, double.class,
double.class, double.class, double.class
);

Object newShape = boxMethod.invoke(null,
0.0625D, 0.0D, 0.0625D,
0.9375D, 0.015625D, 0.9375D
);

// Bypass: use Unsafe to smash static final SHAPE
Field shapeField = lilyClass.getDeclaredField("SHAPE");
shapeField.setAccessible(true);

Class<?> unsafeClass = Class.forName("sun.misc.Unsafe");
Field theUnsafeField = unsafeClass.getDeclaredField("theUnsafe");
theUnsafeField.setAccessible(true);
Object unsafe = theUnsafeField.get(null);

Method staticFieldOffset = unsafeClass.getMethod("staticFieldOffset", Field.class);
Method staticFieldBase = unsafeClass.getMethod("staticFieldBase", Field.class);
Method putObjectVolatile = unsafeClass.getMethod("putObjectVolatile", Object.class, long.class, Object.class);

long offset = (long) staticFieldOffset.invoke(unsafe, shapeField);
Object baseObj = staticFieldBase.invoke(unsafe, shapeField);

// This actually overwrites the static final field
putObjectVolatile.invoke(unsafe, baseObj, offset, newShape);

logger.info("Patched lily pad SHAPE for 1.20.5+ via Unsafe bypass");
return;
}

// Legacy path (pre 1.20.5)
final Field boundingBoxField = getFieldAccessible(getNMSBlockClass("BlockWaterLily"), serverVersion.olderThanOrEqualTo(ProtocolVersion.v1_20_2) ? "a" : "b");

setBoundingBox(boundingBoxField.get(null), 0.0625, 0.0, 0.0625, 0.9375, 0.015625, 0.9375);
} catch (Exception ex) {
logger.log(Level.SEVERE, "Could not fix lily pad bounding box.", ex);
}
}

public static void fixCarpet(final Logger logger, final ProtocolVersion serverVersion) {
try {
// Modern Mojang runtime (1.20.5+ including 26.x)
if (serverVersion.newerThanOrEqualTo(ProtocolVersion.v1_20_5)) {
logger.warning("Skipping carpet collision fix on Mojang 1.20.5+ (SHAPE is static final).");
return;
}
// Legacy path (pre 1.20.5)
final Class<?> blockCarpetClass = serverVersion.olderThanOrEqualTo(ProtocolVersion.v1_16_4) ? getNMSBlockClass("BlockCarpet") : getNMSBlockClass("CarpetBlock");

final Field boundingBoxField = getFieldAccessible(blockCarpetClass, serverVersion.olderThanOrEqualTo(ProtocolVersion.v1_20_2) ? "a" : "b");
Expand All @@ -59,43 +110,46 @@ public static void fixCarpet(final Logger logger, final ProtocolVersion serverVe
public static void fixLadder(final Logger logger, final ProtocolVersion serverVersion) {
try {
if (serverVersion.newerThanOrEqualTo(ProtocolVersion.v1_20_5)) {
final Class<?> blockLadderClass = getNMSBlockClass("BlockLadder");

final Map<String, double[]> overrides = new HashMap<String, double[]>();
overrides.put("EAST", new double[]{0.0D, 0.0D, 0.0D, 0.125D, 1.0D, 1.0D});
overrides.put("WEST", new double[]{0.875D, 0.0D, 0.0D, 1.0D, 1.0D, 1.0D});
overrides.put("SOUTH", new double[]{0.0D, 0.0D, 0.0D, 1.0D, 1.0D, 0.125D});
overrides.put("NORTH", new double[]{0.0D, 0.0D, 0.875D, 1.0D, 1.0D, 1.0D});

Map<Object, Object> shapesMap = null;
for (Field field : blockLadderClass.getDeclaredFields()) {
if (!Modifier.isStatic(field.getModifiers())) {
continue;
}
if (!Map.class.isAssignableFrom(field.getType())) {
continue;
}
field.setAccessible(true);
final Object value = field.get(null);
if (value instanceof Map<?, ?>) {
@SuppressWarnings("unchecked") final Map<Object, Object> casted = (Map<Object, Object>) value;
shapesMap = casted;
break;
}
}

boolean updated = false;
if (shapesMap != null) {
updated = updateShapesMap(shapesMap, overrides);
}

if (!updated) {
updated = updateShapeConstants(blockLadderClass, overrides);
}

if (!updated) {
throw new IllegalStateException("Could not adjust ladder shapes for modern versions");
}

// Mojang class name
Class<?> ladderBlockClass = Class.forName("net.minecraft.world.level.block.LadderBlock");

// Shapes.box(...) for VoxelShape creation
Class<?> shapesClass = Class.forName("net.minecraft.world.phys.shapes.Shapes");
Method boxMethod = shapesClass.getMethod(
"box",
double.class, double.class, double.class,
double.class, double.class, double.class
);

Class<?> directionClass = Class.forName("net.minecraft.core.Direction");
// Direction enum
Object EAST = directionClass.getField("EAST").get(null);
Object WEST = directionClass.getField("WEST").get(null);
Object SOUTH = directionClass.getField("SOUTH").get(null);
Object NORTH = directionClass.getField("NORTH").get(null);

// Build shapes
Object eastShape = boxMethod.invoke(null, 0.0D, 0.0D, 0.0D, 0.125D, 1.0D, 1.0D);
Object westShape = boxMethod.invoke(null, 0.875D, 0.0D, 0.0D, 1.0D, 1.0D, 1.0D);
Object southShape = boxMethod.invoke(null, 0.0D, 0.0D, 0.0D, 1.0D, 1.0D, 0.125D);
Object northShape = boxMethod.invoke(null, 0.0D, 0.0D, 0.875D, 1.0D, 1.0D, 1.0D);

// Replace LadderBlock.SHAPES contents (cannot reassign final field!)
Field shapesField = ladderBlockClass.getDeclaredField("SHAPES");
shapesField.setAccessible(true);

@SuppressWarnings("unchecked")
Map<Object, Object> shapesMap = (Map<Object, Object>) shapesField.get(null);

shapesMap.clear();
shapesMap.put(EAST, eastShape);
shapesMap.put(WEST, westShape);
shapesMap.put(SOUTH, southShape);
shapesMap.put(NORTH, northShape);

logger.info("Successfully patched ladder collision shapes for Mojang 26.2+");
return;
} else {
final boolean pre1_12_2 = serverVersion.olderThanOrEqualTo(ProtocolVersion.v1_12_2);
final boolean pre1_13_2 = serverVersion.olderThanOrEqualTo(ProtocolVersion.v1_13_2);
Expand Down