Fix momentum

src/main/java/com/viaversion/viafabricplus/injection/mixin/features/movement/constants/MixinEntity.java

@@ -23,7 +23,9 @@
 
 import com.viaversion.viafabricplus.protocoltranslator.ProtocolTranslator;
 import com.viaversion.viaversion.api.protocol.version.ProtocolVersion;
+import net.minecraft.util.Mth;
 import net.minecraft.world.entity.Entity;
+import net.minecraft.world.phys.Vec3;
 import org.spongepowered.asm.mixin.Mixin;
 import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Constant;
@@ -45,12 +47,33 @@ private double fixBlockCollisionMargin(double constant) {
         }
     }
 
-    @ModifyConstant(method = "getInputVector", constant = @Constant(doubleValue = 1E-7))
-    private static double fixVelocityEpsilon(double epsilon) {
+    @Inject(method = "getInputVector", at = @At("HEAD"), cancellable = true)
+    private static void fixInputVector(Vec3 input, float speed, float yRot, CallbackInfoReturnable<Vec3> cir) {
         if (ProtocolTranslator.getTargetVersion().olderThanOrEqualTo(ProtocolVersion.v1_13_2)) {
-            return 1E-4;
-        } else {
-            return epsilon;
+            float x = (float) input.x;
+            float z = (float) input.z;
+
+            float length = x * x + z * z;
+
+            if (length < 1.0E-4F) {
+                cir.setReturnValue(Vec3.ZERO);
+            }
+
+            length = Math.max(Mth.sqrt(length), 1.0F);
+
+            final float scale = speed / length;
+
+            x *= scale;
+            z *= scale;
+
+            final float sin = Mth.sin(yRot * (float) (Math.PI / 180.0));
+            final float cos = Mth.cos(yRot * (float) (Math.PI / 180.0));
+
+            cir.setReturnValue(new Vec3(
+                x * cos - z * sin,
+                input.y,
+                z * cos + x * sin
+            ));
         }
     }
 

src/main/java/com/viaversion/viafabricplus/injection/mixin/features/movement/limitation/MixinLivingEntity.java

@@ -35,8 +35,10 @@
 import org.spongepowered.asm.mixin.Shadow;
 import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Constant;
+import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.ModifyConstant;
 import org.spongepowered.asm.mixin.injection.Redirect;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;
 
 @Mixin(LivingEntity.class)
 public abstract class MixinLivingEntity extends Entity {
@@ -45,6 +47,12 @@ public MixinLivingEntity(EntityType<?> type, Level world) {
         super(type, world);
     }
 
+    @Shadow
+    public abstract float getSpeed();
+
+    @Shadow
+    protected abstract float getFlyingSpeed();
+
     @Shadow
     public abstract boolean hasEffect(Holder<MobEffect> effect);
 
@@ -57,6 +65,15 @@ private double allowFrictionLessThan(double constant) {
         }
     }
 
+    @Inject(method = "getFrictionInfluencedSpeed", at = @At("HEAD"), cancellable = true)
+    private void modifyFrictionInfluencedSpeed(float blockFriction, CallbackInfoReturnable<Float> cir) {
+        if (ProtocolTranslator.getTargetVersion().olderThanOrEqualTo(ProtocolVersion.v1_13_2)) {
+            float drag = this.onGround() ? blockFriction * 0.91F : 0.91F;
+            float accel = 0.16277136F / (drag * drag * drag);
+            cir.setReturnValue(this.onGround() ? this.getSpeed() * accel : this.getFlyingSpeed());
+        }
+    }
+
     @Redirect(method = "aiStep", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/entity/LivingEntity;is(Ljava/lang/Object;)Z"))
     private boolean useEuclideanDistanceCalculation(LivingEntity instance, Object o) {
         if (ProtocolTranslator.getTargetVersion().olderThanOrEqualTo(ProtocolVersion.v1_21_4)) {