Add TRANS_SPRING to Tween

doc/classes/Tween.xml

@@ -501,6 +501,9 @@
 		<constant name="TRANS_BACK" value="10" enum="TransitionType">
 			The animation is interpolated backing out at ends.
 		</constant>
+		<constant name="TRANS_SPRING" value="11" enum="TransitionType">
+			The animation is interpolated like a spring towards the end.
+		</constant>
 		<constant name="EASE_IN" value="0" enum="EaseType">
 			The interpolation starts slowly and speeds up towards the end.
 		</constant>

scene/animation/easing_equations.h

@@ -413,4 +413,33 @@ static real_t out_in(real_t t, real_t b, real_t c, real_t d) {
 }
 }; // namespace back
 
+namespace spring {
+static real_t out(real_t t, real_t b, real_t c, real_t d) {
+	t /= d;
+	real_t s = 1.0 - t;
+	t = (sin(t * Math_PI * (0.2 + 2.5 * t * t * t)) * pow(s, 2.2) + t) * (1.0 + (1.2 * s));
+	return c * t + b;
+}
+
+static real_t in(real_t t, real_t b, real_t c, real_t d) {
+	return c - out(d - t, 0, c, d) + b;
+}
+
+static real_t in_out(real_t t, real_t b, real_t c, real_t d) {
+	if (t < d / 2) {
+		return in(t * 2, b, c / 2, d);
+	}
+	real_t h = c / 2;
+	return out(t * 2 - d, b + h, h, d);
+}
+
+static real_t out_in(real_t t, real_t b, real_t c, real_t d) {
+	if (t < d / 2) {
+		return out(t * 2, b, c / 2, d);
+	}
+	real_t h = c / 2;
+	return in(t * 2 - d, b + h, h, d);
+}
+}; // namespace spring
+
 #endif // EASING_EQUATIONS_H

scene/animation/tween.cpp

@@ -50,6 +50,7 @@ Tween::interpolater Tween::interpolaters[Tween::TRANS_MAX][Tween::EASE_MAX] = {
 	{ &circ::in, &circ::out, &circ::in_out, &circ::out_in },
 	{ &bounce::in, &bounce::out, &bounce::in_out, &bounce::out_in },
 	{ &back::in, &back::out, &back::in_out, &back::out_in },
+	{ &spring::in, &spring::out, &spring::in_out, &spring::out_in },
 };
 
 void Tweener::set_tween(const Ref<Tween> &p_tween) {
@@ -483,6 +484,7 @@ void Tween::_bind_methods() {
 	BIND_ENUM_CONSTANT(TRANS_CIRC);
 	BIND_ENUM_CONSTANT(TRANS_BOUNCE);
 	BIND_ENUM_CONSTANT(TRANS_BACK);
+	BIND_ENUM_CONSTANT(TRANS_SPRING);
 
 	BIND_ENUM_CONSTANT(EASE_IN);
 	BIND_ENUM_CONSTANT(EASE_OUT);

scene/animation/tween.h

@@ -87,6 +87,7 @@ public:
 		TRANS_CIRC,
 		TRANS_BOUNCE,
 		TRANS_BACK,
+		TRANS_SPRING,
 		TRANS_MAX
 	};