add easing functions

Author: g-harel

internal/animate/ease.ts

@@ -0,0 +1,17 @@
+import {InterpolationFunc} from "./types";
+
+export const linear: InterpolationFunc = (progress: number) => {
+    return progress;
+}
+
+export const ease: InterpolationFunc = (progress: number) => {
+    return 0.5 + 0.5 * Math.sin(Math.PI * (progress + 1.5));
+};
+
+export const easeStart: InterpolationFunc = (progress: number) => {
+    return progress ** 2;
+};
+
+export const easeEnd: InterpolationFunc = (progress: number) => {
+    return 1 - (progress - 1) ** 2;
+};

internal/animate/interpolate.ts

@@ -2,7 +2,6 @@ import {Shape} from "../types";
 import {split, splitLine, mod} from "../util";
 
 // TODO percentage > 1
-// TODO interpolation function (ex. easing)
 
 const interpolateAngle = (percentage: number, a: number, b: number): number => {
     const tau = Math.PI * 2;

internal/animate/types.ts

@@ -1,11 +1,3 @@
-import {Shape} from "../types";
-
-export interface EasingFunc {
+export interface InterpolationFunc {
     (progress: number): number;
 }
-
-export interface Keyframe {
-    shape: Shape;
-    easeIn: EasingFunc;
-    easeOut: EasingFunc;
-}