From ddf3bc9d2aca338c64e2aa679d23b402e994bd3a Mon Sep 17 00:00:00 2001
From: Amy Wilder <henrythepony@gmail.com>
Date: Sun, 3 Aug 2025 12:46:41 -0400
Subject: [PATCH] Add inverse point functions

---
 src/raylib.h  |  4 ++++
 src/rshapes.c | 24 ++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/raylib.h b/src/raylib.h
index 8473fd5fe..d588084cb 100644
--- a/src/raylib.h
+++ b/src/raylib.h
@@ -1310,6 +1310,10 @@ RLAPI Vector2 GetSplinePointCatmullRom(Vector2 p1, Vector2 p2, Vector2 p3, Vecto
 RLAPI Vector2 GetSplinePointBezierQuad(Vector2 p1, Vector2 c2, Vector2 p3, float t);                     // Get (evaluate) spline point: Quadratic Bezier
 RLAPI Vector2 GetSplinePointBezierCubic(Vector2 p1, Vector2 c2, Vector2 c3, Vector2 p4, float t);        // Get (evaluate) spline point: Cubic Bezier
 
+// Spline inverse point functions, for evenly-spaced points on the curve
+RLAPI void GetSplineControlBezierQuad(Vector2 startPos, Vector2 midPos, Vector2 endPos, Vector2 *controlPos); // Get (evaluate) spline control point: Quadratic Bezier
+RLAPI void GetSplineControlBezierCubic(Vector2 startPos, Vector2 oneThirdsPos, Vector2 twoThirdsPos, Vector2 endPos, Vector2 *startControlPos, Vector2 *endControlPos); // Get (evaluate) spline control points: Cubic Bezier
+
 // Spline segment slope evaluation functions, for a given t [0.0f .. 1.0f]
 RLAPI Vector2 GetSplineVelocityLinear(Vector2 startPos, Vector2 endPos);                                 // Get (evaluate) spline velocity: Linear
 RLAPI Vector2 GetSplineVelocityBezierQuad(Vector2 startPos, Vector2 controlPos, Vector2 endPos, float t); // Get (evaluate) spline velocity: Quadratic Bezier
diff --git a/src/rshapes.c b/src/rshapes.c
index 8674917df..976a2c69a 100644
--- a/src/rshapes.c
+++ b/src/rshapes.c
@@ -2358,6 +2358,14 @@ Vector2 GetSplinePointBezierQuad(Vector2 startPos, Vector2 controlPos, Vector2 e
     return point;
 }
 
+// Get spline control point given evenly-spaced points on that curve, Quadratic Bezier
+// NOTE: Assumes startPos has 0 entry velocity and endPos has 0 exit velocity
+void GetSplineControlBezierQuad(Vector2 startPos, Vector2 midPos, Vector2 endPos, Vector2 *controlPos)
+{
+    controlPos->y = 2.0f*midPos.y - 0.5f*(startPos.y + endPos.y);
+    controlPos->x = 2.0f*midPos.x - 0.5f*(startPos.x + endPos.x);
+}
+
 // Get spline point for a given t [0.0f .. 1.0f], Cubic Bezier
 Vector2 GetSplinePointBezierCubic(Vector2 startPos, Vector2 startControlPos, Vector2 endControlPos, Vector2 endPos, float t)
 {
@@ -2374,6 +2382,22 @@ Vector2 GetSplinePointBezierCubic(Vector2 startPos, Vector2 startControlPos, Vec
     return point;
 }
 
+// Get spline control points given evenly-spaced points on that curve, Cubic Bezier
+// NOTE: Assumes startPos has 0 entry velocity and endPos has 0 exit velocity
+void GetSplineControlBezierCubic(Vector2 startPos, Vector2 oneThirdsPos, Vector2 twoThirdsPos, Vector2 endPos, Vector2 *startControlPos, Vector2 *endControlPos)
+{
+    const float a = -5.0f/6.0f;
+    const float b = 3.0f;
+    const float c = -3.0f/2.0f;
+    const float d = 1.0f/3.0f;
+
+    startControlPos->x = a*startPos.x + b*oneThirdsPos.x + c*twoThirdsPos.x + d*endPos.x;
+    startControlPos->y = a*startPos.y + b*oneThirdsPos.y + c*twoThirdsPos.y + d*endPos.y;
+
+    endControlPos->x = a*endPos.x + b*twoThirdsPos.x + c*oneThirdsPos.x + d*startPos.x;
+    endControlPos->y = a*endPos.y + b*twoThirdsPos.y + c*oneThirdsPos.y + d*startPos.y;
+}
+
 // Get spline direction and speed, Linear Bezier
 //
 // Normalize to get the "forward" direction of the curve