Rename VectorUtils to OsuHitObjectGenerationUtils

osu.Game.Rulesets.Osu/Utils/OsuHitObjectGenerationUtils.cs

@@ -0,0 +1,104 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Game.Rulesets.Osu.UI;
+using osuTK;
+
+namespace osu.Game.Rulesets.Osu.Utils
+{
+    public static class OsuHitObjectGenerationUtils
+    {
+        // The relative distance to the edge of the playfield before objects' positions should start to "turn around" and curve towards the middle.
+        // The closer the hit objects draw to the border, the sharper the turn
+        private const float playfield_edge_ratio = 0.375f;
+
+        private static readonly float border_distance_x = OsuPlayfield.BASE_SIZE.X * playfield_edge_ratio;
+        private static readonly float border_distance_y = OsuPlayfield.BASE_SIZE.Y * playfield_edge_ratio;
+
+        private static readonly Vector2 playfield_middle = OsuPlayfield.BASE_SIZE / 2;
+
+        /// <summary>
+        /// Rotate a hit object away from the playfield edge, while keeping a constant distance
+        /// from the previous object.
+        /// </summary>
+        /// <remarks>
+        /// The extent of rotation depends on the position of the hit object. Hit objects
+        /// closer to the playfield edge will be rotated to a larger extent.
+        /// </remarks>
+        /// <param name="prevObjectPos">Position of the previous hit object.</param>
+        /// <param name="posRelativeToPrev">Position of the hit object to be rotated, relative to the previous hit object.</param>
+        /// <param name="rotationRatio">
+        /// The extent of rotation.
+        /// 0 means the hit object is never rotated.
+        /// 1 means the hit object will be fully rotated towards playfield center when it is originally at playfield edge.
+        /// </param>
+        /// <returns>The new position of the hit object, relative to the previous one.</returns>
+        public static Vector2 RotateAwayFromEdge(Vector2 prevObjectPos, Vector2 posRelativeToPrev, float rotationRatio = 0.5f)
+        {
+            var relativeRotationDistance = 0f;
+
+            if (prevObjectPos.X < playfield_middle.X)
+            {
+                relativeRotationDistance = Math.Max(
+                    (border_distance_x - prevObjectPos.X) / border_distance_x,
+                    relativeRotationDistance
+                );
+            }
+            else
+            {
+                relativeRotationDistance = Math.Max(
+                    (prevObjectPos.X - (OsuPlayfield.BASE_SIZE.X - border_distance_x)) / border_distance_x,
+                    relativeRotationDistance
+                );
+            }
+
+            if (prevObjectPos.Y < playfield_middle.Y)
+            {
+                relativeRotationDistance = Math.Max(
+                    (border_distance_y - prevObjectPos.Y) / border_distance_y,
+                    relativeRotationDistance
+                );
+            }
+            else
+            {
+                relativeRotationDistance = Math.Max(
+                    (prevObjectPos.Y - (OsuPlayfield.BASE_SIZE.Y - border_distance_y)) / border_distance_y,
+                    relativeRotationDistance
+                );
+            }
+
+            return RotateVectorTowardsVector(
+                posRelativeToPrev,
+                playfield_middle - prevObjectPos,
+                Math.Min(1, relativeRotationDistance * rotationRatio)
+            );
+        }
+
+        /// <summary>
+        /// Rotates vector "initial" towards vector "destination".
+        /// </summary>
+        /// <param name="initial">The vector to be rotated.</param>
+        /// <param name="destination">The vector that "initial" should be rotated towards.</param>
+        /// <param name="rotationRatio">How much "initial" should be rotated. 0 means no rotation. 1 means "initial" is fully rotated to equal "destination".</param>
+        /// <returns>The rotated vector.</returns>
+        public static Vector2 RotateVectorTowardsVector(Vector2 initial, Vector2 destination, float rotationRatio)
+        {
+            var initialAngleRad = Math.Atan2(initial.Y, initial.X);
+            var destAngleRad = Math.Atan2(destination.Y, destination.X);
+
+            var diff = destAngleRad - initialAngleRad;
+
+            while (diff < -Math.PI) diff += 2 * Math.PI;
+
+            while (diff > Math.PI) diff -= 2 * Math.PI;
+
+            var finalAngleRad = initialAngleRad + rotationRatio * diff;
+
+            return new Vector2(
+                initial.Length * (float)Math.Cos(finalAngleRad),
+                initial.Length * (float)Math.Sin(finalAngleRad)
+            );
+        }
+    }
+}