[libhandy] animation: Add hdy_ease_in_cubic()

[Adrien Plazas <aplazas src gnome org>]

commit 1ed33ec217cf85647707a0cdf393e7a8d1af2edc
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Sun Sep 13 02:14:18 2020 +0500

    animation: Add hdy_ease_in_cubic()

 src/hdy-animation-private.h | 1 +
 src/hdy-animation.c         | 6 ++++++
 2 files changed, 7 insertions(+)
---
diff --git a/src/hdy-animation-private.h b/src/hdy-animation-private.h
index ed6362f0..a24f3daa 100644
--- a/src/hdy-animation-private.h
+++ b/src/hdy-animation-private.h
@@ -45,5 +45,6 @@ gdouble       hdy_animation_get_value (HdyAnimation *self);
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (HdyAnimation, hdy_animation_unref)
 
 gdouble hdy_lerp (gdouble a, gdouble b, gdouble t);
+gdouble hdy_ease_in_cubic (gdouble t);
 
 G_END_DECLS
diff --git a/src/hdy-animation.c b/src/hdy-animation.c
index 66ed3d64..db71612a 100644
--- a/src/hdy-animation.c
+++ b/src/hdy-animation.c
@@ -248,3 +248,9 @@ hdy_ease_out_cubic (gdouble t)
   gdouble p = t - 1;
   return p * p * p + 1;
 }
+
+gdouble
+hdy_ease_in_cubic (gdouble t)
+{
+  return t * t * t;
+}