0.15 Release Notes: Easing curves (#1790)

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

release-content/0.15/release-notes/15675_Add_most_common_interpolations.md

@@ -1,4 +1,31 @@
 <!-- Add most common interpolations -->
 <!-- https://github.com/bevyengine/bevy/pull/15675 -->
 
-<!-- TODO -->
+"Easing functions" can be used to easily construct curves that interpolate between two values.
+There are many "common" easing functions that each have a different "character" to them. These
+are often used in "tweening" scenarios to give life to the interpolation.
+
+<video controls><source src="ease-functions.mp4" type="video/mp4"/></video>
+
+**Bevy 0.15** adds a new `Ease` trait, which defines how to interpolate a value of a given type. The `Ease` types include:
+
+* vector types (`f32`, `Vec2`, `Vec3`, ...);
+* direction types (`Dir2`, `Dir3`, `Dir3A`);
+* rotation types (`Rot2`, `Quat`).
+
+We've also added an `EaseFunction` enum, which defines many common easing functions. The new `easing_curve` constructor uses these as inputs to define a final `Curve` from the given easing parameters.
+
+For example, we can use an easing function to interpolate between two rotations:
+
+```rust
+// Ease between no rotation and a rotation of angle PI/2 about the y-axis.
+let rotation_curve = easing_curve(
+    Quat::IDENTITY,
+    Quat::from_rotation_y(FRAC_PI_2),
+    EaseFunction::ElasticInOut,
+)
+.reparametrize_linear(interval(0.0, 4.0).unwrap())
+.unwrap();
+```
+
+<video controls><source src="eased-rotation.mp4" type="video/mp4"/></video>

release-content/0.15/release-notes/_release-notes.toml

@@ -383,9 +383,9 @@ file_name = "15627_Add_more_tools_for_traversing_hierarchies.md"
 
 [[release_notes]]
 title = "Add most common interpolations"
-authors = ["@mockersf"]
-contributors = []
-prs = [15675]
+authors = ["@RobWalt", "@mockersf", "@mweatherley"]
+contributors = ["@NthTensor", "@eckz", "@alice-i-cecile"]
+prs = [14788, 15675, 15711]
 file_name = "15675_Add_most_common_interpolations.md"
 
 [[release_notes]]