Better onGround check

Thanks to @AJ-Ferguson for the suggestion.

Includes hacks to still maintain pre-1.21.30, but that will likely lose support very soon, anyway.

core/src/main/java/org/geysermc/geyser/level/physics/CollisionManager.java

@@ -154,10 +154,11 @@ public class CollisionManager {
      * the two versions. Will also send corrected movement packets back to Bedrock if they collide with pistons.
      *
      * @param bedrockPosition the current Bedrock position of the client
+     * @param onGround whether the Bedrock player is on the ground
      * @param teleported whether the Bedrock player has teleported to a new position. If true, movement correction is skipped.
      * @return the position to send to the Java server, or null to cancel sending the packet
      */
-    public @Nullable CollisionResult adjustBedrockPosition(Vector3f bedrockPosition, boolean teleported) {
+    public @Nullable CollisionResult adjustBedrockPosition(Vector3f bedrockPosition, boolean onGround, boolean teleported) {
         PistonCache pistonCache = session.getPistonCache();
         // Bedrock clients tend to fall off of honey blocks, so we need to teleport them to the new position
         if (pistonCache.isPlayerAttachedToHoney()) {
@@ -198,9 +199,9 @@ public class CollisionManager {
 
         position = playerBoundingBox.getBottomCenter();
 
-        boolean onGround = (adjustedMovement.getY() != movement.getY() && movement.getY() < 0) || isOnGround();
+        boolean newOnGround = adjustedMovement.getY() != movement.getY() && movement.getY() < 0 || onGround;
         // Send corrected position to Bedrock if they differ by too much to prevent de-syncs
-        if (movement.distanceSquared(adjustedMovement) > INCORRECT_MOVEMENT_THRESHOLD) {
+        if (onGround != newOnGround || movement.distanceSquared(adjustedMovement) > INCORRECT_MOVEMENT_THRESHOLD) {
             PlayerEntity playerEntity = session.getPlayerEntity();
             // Client will dismount if on a vehicle
             if (playerEntity.getVehicle() == null && pistonCache.getPlayerMotion().equals(Vector3f.ZERO) && !pistonCache.isPlayerSlimeCollision()) {
@@ -208,7 +209,7 @@ public class CollisionManager {
             }
         }
 
-        if (!onGround) {
+        if (!newOnGround) {
             // Trim the position to prevent rounding errors that make Java think we are clipping into a block
             position = Vector3d.from(position.getX(), Double.parseDouble(DECIMAL_FORMAT.format(position.getY())), position.getZ());
         }
@@ -415,8 +416,8 @@ public class CollisionManager {
         return BlockUtils.getCollision(blockId);
     }
 
-    private boolean isOnGround() {
-        // Someone smarter than me at collisions plz check this.
+    public boolean isOnGround() {
+        // Temporary until pre-1.21.30 support is dropped.
         Vector3d bottomCenter = playerBoundingBox.getBottomCenter();
         Vector3i groundPos = Vector3i.from(bottomCenter.getX(), bottomCenter.getY() - 1, bottomCenter.getZ());
         BlockCollision collision = BlockUtils.getCollisionAt(session, groundPos);

core/src/main/java/org/geysermc/geyser/network/GameProtocol.java

@@ -111,6 +111,10 @@ public final class GameProtocol {
         return session.getUpstream().getProtocolVersion() < Bedrock_v686.CODEC.getProtocolVersion();
     }
 
+    public static boolean isPre1_21_30(GeyserSession session) {
+        return session.getUpstream().getProtocolVersion() < Bedrock_v729.CODEC.getProtocolVersion();
+    }
+
     public static boolean isPre1_21_40(GeyserSession session) {
         return session.getUpstream().getProtocolVersion() < Bedrock_v748.CODEC.getProtocolVersion();
     }

core/src/main/java/org/geysermc/geyser/translator/protocol/bedrock/entity/player/input/BedrockMovePlayer.java

@@ -25,6 +25,7 @@
 
 package org.geysermc.geyser.translator.protocol.bedrock.entity.player.input;
 
+import net.kyori.adventure.util.TriState;
 import org.cloudburstmc.math.vector.Vector3d;
 import org.cloudburstmc.math.vector.Vector3f;
 import org.cloudburstmc.protocol.bedrock.data.PlayerAuthInputData;
@@ -32,6 +33,7 @@ import org.cloudburstmc.protocol.bedrock.packet.PlayerAuthInputPacket;
 import org.geysermc.geyser.entity.EntityDefinitions;
 import org.geysermc.geyser.entity.type.player.SessionPlayerEntity;
 import org.geysermc.geyser.level.physics.CollisionResult;
+import org.geysermc.geyser.network.GameProtocol;
 import org.geysermc.geyser.session.GeyserSession;
 import org.geysermc.geyser.text.ChatColor;
 import org.geysermc.mcprotocollib.network.packet.Packet;
@@ -86,6 +88,14 @@ final class BedrockMovePlayer {
             session.setLookBackScheduledFuture(null);
         }
 
+        TriState maybeOnGround;
+        if (GameProtocol.isPre1_21_30(session)) {
+            // VERTICAL_COLLISION input data does not exist.
+            maybeOnGround = TriState.NOT_SET;
+        } else {
+            // Client is telling us it wants to move down, but something is blocking it from doing so.
+            maybeOnGround = TriState.byBoolean(packet.getInputData().contains(PlayerAuthInputData.VERTICAL_COLLISION) && packet.getDelta().getY() < 0);
+        }
         // This takes into account no movement sent from the client, but the player is trying to move anyway.
         // (Press into a wall in a corner - you're trying to move but nothing actually happens)
         boolean horizontalCollision = packet.getInputData().contains(PlayerAuthInputData.HORIZONTAL_COLLISION);
@@ -94,7 +104,7 @@ final class BedrockMovePlayer {
         // This isn't needed, but it makes the packets closer to vanilla
         // It also means you can't "lag back" while only looking, in theory
         if (!positionChanged && rotationChanged) {
-            ServerboundMovePlayerRotPacket playerRotationPacket = new ServerboundMovePlayerRotPacket(entity.isOnGround(), horizontalCollision, yaw, pitch);
+            ServerboundMovePlayerRotPacket playerRotationPacket = new ServerboundMovePlayerRotPacket(maybeOnGround.toBooleanOrElse(entity.isOnGround()), horizontalCollision, yaw, pitch);
 
             entity.setYaw(yaw);
             entity.setPitch(pitch);
@@ -103,10 +113,10 @@ final class BedrockMovePlayer {
             session.sendDownstreamGamePacket(playerRotationPacket);
         } else if (positionChanged) {
             if (isValidMove(session, entity.getPosition(), packet.getPosition())) {
-                CollisionResult result = session.getCollisionManager().adjustBedrockPosition(packet.getPosition(), packet.getInputData().contains(PlayerAuthInputData.HANDLE_TELEPORT));
+                CollisionResult result = session.getCollisionManager().adjustBedrockPosition(packet.getPosition(), maybeOnGround.toBooleanOrElse(false), packet.getInputData().contains(PlayerAuthInputData.HANDLE_TELEPORT));
                 if (result != null) { // A null return value cancels the packet
                     Vector3d position = result.correctedMovement();
-                    boolean onGround = result.onGround().toBooleanOrElse(entity.isOnGround());
+                    boolean onGround = maybeOnGround.toBooleanOrElseGet(() -> session.getCollisionManager().isOnGround());
                     boolean isBelowVoid = entity.isVoidPositionDesynched();
 
                     boolean teleportThroughVoidFloor, mustResyncPosition;
@@ -155,7 +165,6 @@ final class BedrockMovePlayer {
                     }
 
                     entity.setPositionManual(packet.getPosition());
-                    entity.setOnGround(onGround);
 
                     // Send final movement changes
                     session.sendDownstreamGamePacket(movePacket);
@@ -174,11 +183,12 @@ final class BedrockMovePlayer {
                 session.getGeyser().getLogger().debug("Recalculating position...");
                 session.getCollisionManager().recalculatePosition();
             }
-        } else if (horizontalCollision != session.getInputCache().lastHorizontalCollision()) {
-            session.sendDownstreamGamePacket(new ServerboundMovePlayerStatusOnlyPacket(entity.isOnGround(), horizontalCollision));
+        } else if (horizontalCollision != session.getInputCache().lastHorizontalCollision() || maybeOnGround.toBooleanOrElse(entity.isOnGround()) != entity.isOnGround()) {
+            session.sendDownstreamGamePacket(new ServerboundMovePlayerStatusOnlyPacket(maybeOnGround.toBooleanOrElse(false), horizontalCollision));
         }
 
         session.getInputCache().setLastHorizontalCollision(horizontalCollision);
+        entity.setOnGround(maybeOnGround.toBooleanOrElse(entity.isOnGround()));
 
         // Move parrots to match if applicable
         if (entity.getLeftParrot() != null) {