Tackle some of the issues with Elytra but without end rod (unfinished).

Missing:
* More testing and adjusting.
* Other cases found, but not yet done. E.g. multiple 0-ydistchange.
* Jumping with oddd gain (2x 3.8 instead 0.42 + 0.33333).
* Lost ground and all the cases apply here (use only sf or refactor).

NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/moving/MovingListener.java

@@ -68,6 +68,7 @@
 import fr.neatmonster.nocheatplus.checks.moving.velocity.SimpleEntry;
 import fr.neatmonster.nocheatplus.checks.net.NetConfig;
 import fr.neatmonster.nocheatplus.checks.net.NetData;
+import fr.neatmonster.nocheatplus.compat.Bridge1_9;
 import fr.neatmonster.nocheatplus.compat.BridgeEnchant;
 import fr.neatmonster.nocheatplus.compat.BridgeHealth;
 import fr.neatmonster.nocheatplus.compat.BridgeMisc;
@@ -942,9 +943,9 @@ private Location checkExtremeMove(final Player player, final PlayerLocation from
      * @param tick
      * @param data
      */
-    private static void workaroundFlyNoFlyTransition(final Player player, final int tick, final MovingData data) {
+    private void workaroundFlyNoFlyTransition(final Player player, final int tick, final MovingData data) {
         final MoveData lastMove = data.moveData.getFirst();
-        final double amount = lastMove.hDistance * (1.0 + Magic.FRICTION_MEDIUM_AIR) / 2.0; // Allow same speed instead?
+        final double amount = guessFlyNoFlyVelocity(player, data.thisMove, lastMove, data);
         data.clearActiveHorVel(); // Clear active velocity due to adding actual speed here.
         data.addHorizontalVelocity(new AccountEntry(tick, amount, 1, MovingData.getHorVelValCount(amount)));
         data.addVerticalVelocity(new SimpleEntry(lastMove.yDistance, 2));
@@ -953,7 +954,32 @@ private static void workaroundFlyNoFlyTransition(final Player player, final int
         // Reset fall height.
         // TODO: Later (e.g. 1.9) check for the ModelFlying, if fall damage is intended.
         data.clearNoFallData();
-        player.setFallDistance(0f);
+        player.setFallDistance(0f); // TODO: Might do without this in case of elytra, needs ensure NoFall doesn't kill the player (...).
+        if (data.debug){
+            debug(player, "Fly-nofly transition: Add velocity.");
+        }
+    }
+
+    private static double guessFlyNoFlyVelocity(final Player player, final MoveData thisMove, final MoveData lastMove, final MovingData data) {
+        // Default margin: Allow slightly less than the previous speed.
+        final double defaultAmount = lastMove.hDistance * (1.0 + Magic.FRICTION_MEDIUM_AIR) / 2.0;
+        // Test for exceptions.
+        if (Bridge1_9.isWearingElytra(player) && thisMove.hDistance > defaultAmount) {
+            // Allowing the same speed won't always work on elytra (still increasing, differing modeling on client side with motXYZ).
+            final MoveData pastMove1 = data.moveData.get(1);
+            if (pastMove1.toIsValid && lastMove.modelFlying != null && pastMove1.modelFlying != null
+                    && thisMove.yDistance < Magic.GLIDE_DESCEND_PHASE_MIN
+                    && lastMove.yDistance < Magic.GLIDE_DESCEND_PHASE_MIN
+                    && pastMove1.yDistance < Magic.GLIDE_DESCEND_PHASE_MIN
+                    && Math.abs(pastMove1.yDistance - lastMove.yDistance) < Magic.GLIDE_DESCEND_GAIN_MAX
+                    && Math.abs(lastMove.yDistance - thisMove.yDistance) < Magic.GLIDE_DESCEND_GAIN_MAX
+                    && lastMove.hDistance > pastMove1.hDistance && thisMove.hDistance > lastMove.hDistance
+                    && Math.abs(lastMove.hDistance - pastMove1.hDistance) < Magic.GLIDE_HORIZONTAL_GAIN_MAX
+                    && Math.abs(thisMove.hDistance - lastMove.hDistance) < Magic.GLIDE_HORIZONTAL_GAIN_MAX) {
+                return thisMove.hDistance + Magic.GLIDE_HORIZONTAL_GAIN_MAX;
+            }
+        }
+        return defaultAmount;
     }
 
     /**

NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/moving/magic/Magic.java

@@ -45,8 +45,24 @@ public class Magic {
     /** Maximal horizontal buffer. It can be higher, but normal resetting should keep this limit. */
 
     public static final double hBufMax          = 1.0;
+
+    /**
+     * Somewhat arbitrary horizontal speed gain maximum for advance glide phase.
+     */
+    public static final double GLIDE_HORIZONTAL_GAIN_MAX = GRAVITY_SPAN;
+
     // Vertical speeds/modifiers. 
     public static final double climbSpeed       = WALK_SPEED * 1.3; // TODO: Check if the factor is needed!
+    /**
+     * Some kind of minimum y descend speed (note the negative sign), for an
+     * already advanced gliding/falling phase with elytra.
+     */
+    public static final double GLIDE_DESCEND_PHASE_MIN = -Magic.GRAVITY_MAX - Magic.GRAVITY_SPAN;
+    /**
+     * Somewhat arbitrary, advanced glide phase, maximum descend speed gain.
+     * This value is positive.
+     */
+    public static final double GLIDE_DESCEND_GAIN_MAX = GRAVITY_MAX;
 
     // On-ground.
     public static final double Y_ON_GROUND_MIN = 0.00001;

NCPCore/src/main/java/fr/neatmonster/nocheatplus/checks/moving/magic/MagicAir.java

@@ -5,6 +5,7 @@
 import fr.neatmonster.nocheatplus.checks.moving.model.LiftOffEnvelope;
 import fr.neatmonster.nocheatplus.checks.moving.model.MoveData;
 import fr.neatmonster.nocheatplus.checks.workaround.WRPT;
+import fr.neatmonster.nocheatplus.compat.Bridge1_9;
 import fr.neatmonster.nocheatplus.utilities.PlayerLocation;
 
 public class MagicAir {
@@ -327,6 +328,56 @@ private static boolean oddFriction(final double yDistance, final double yDistDif
                                 ;
     }
 
+    /**
+     * Odd behavior with/after wearing elytra. End rod is not in either hand,
+     * elytra is equipped (not checked in here).
+     * 
+     * @param yDistance
+     * @param yDistDiffEx
+     * @param lastMove
+     * @param data
+     * @return
+     */
+    private static boolean oddElytra(final double yDistance, final double yDistDiffEx, final MoveData lastMove, final MovingData data) {
+        // Organize cases differently here, at the cost of reaching some nesting level, in order to see if it's better to overview.
+        final MoveData thisMove = data.thisMove;
+        final MoveData pastMove1 = data.moveData.get(1); // Checked below, if needed.
+        // Both descending moves.
+        if (thisMove.yDistance < 0.0 && lastMove.yDistance < 0.0) {
+            // Falling too slow.
+            if (yDistDiffEx > 0.0) {
+                final double yDistChange = thisMove.yDistance - lastMove.yDistance;
+                // Increase falling speed somehow.
+                if (yDistChange < 0.0) {
+                    // pastMove1 valid, decreasing speed envelope like above.
+                    if (pastMove1.toIsValid && pastMove1.yDistance < 0.0) {
+                        final double lastDecrease = lastMove.yDistance - pastMove1.yDistance;
+                        // Increase falling speed from past to last.
+                        if (lastDecrease < 0.0) {
+                            // Relate sum of decrease to gravity somehow. 
+                            // TODO: Inaugurate by the one below?
+                            if (Math.abs(yDistChange + lastDecrease) > Magic.GRAVITY_ODD / 2.0) {
+                                // TODO: Might further test for a workaround count down or relate to total gain / jump phase.
+                                return true;
+                            }
+                        }
+                    }
+                }
+                // Independently of increasing/decreasing.
+                // Gliding possibly.
+                if (thisMove.yDistance < Magic.GLIDE_DESCEND_PHASE_MIN
+                        && lastMove.yDistance < Magic.GLIDE_DESCEND_PHASE_MIN
+                        && Math.abs(yDistChange) < Magic.GLIDE_DESCEND_GAIN_MAX) {
+                    // Restrict to early falling.
+                    if (data.sfJumpPhase < 20) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
+
     /**
      * Several types of odd in-air moves, mostly with gravity near maximum,
      * friction, medium change. Needs lastMove.toIsValid.
@@ -364,6 +415,10 @@ public static boolean oddJunction(final PlayerLocation from, final PlayerLocatio
             // Odd behavior with moving up or (slightly) down, accounting for more than one past move.
             return true;
         }
+        if (Bridge1_9.isWearingElytra(from.getPlayer()) && MagicAir.oddElytra(yDistance, yDistDiffEx, lastMove, data)) {
+            // Odd behavior with/after wearing elytra.
+            return true;
+        }
         return false;
     }