Add easing functions.

src/textual/_animator.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import asyncio
 import sys
+from math import pi, cos, sin, sqrt
 from time import time
 from tracemalloc import start
 from typing import Callable, TypeVar
@@ -27,14 +28,96 @@ class Animatable(Protocol):
         ...
 
 
+def in_out_expo(x):
+    """https://easings.net/#easeInOutExpo"""
+    if 0 < x < 0.5:
+        return pow(2, 20 * x - 10) / 2
+    elif 0.5 <= x < 1:
+        return (2 - pow(2, -20 * x + 10)) / 2
+    else:
+        return x    # x in (0, 1)
+
+
+def in_out_circ(x):
+    """https://easings.net/#easeInOutCirc"""
+    if x < 0.5:
+        return (1 - sqrt(1 - pow(2 * x, 2))) / 2
+    else:
+        return (sqrt(1 - pow(-2 * x + 2, 2)) + 1) / 2
+
+
+def in_out_back(x):
+    """https://easings.net/#easeInOutBack"""
+    c = 1.70158 * 1.525
+    if x < 0.5:
+        return (pow(2 * x, 2) * ((c + 1) * 2 * x - c)) / 2
+    else:
+        return (pow(2 * x - 2, 2) * ((c + 1) * (x * 2 - 2) + c) + 2) / 2
+
+
+def in_elastic(x):
+    """https://easings.net/#easeInElastic"""
+    c = 2 * pi / 3;
+    if 0 < x < 1:
+        return -pow(2, 10 * x - 10) * sin((x * 10 - 10.75) * c)
+    else:
+        return x
+
+
+def in_out_elastic(x):
+    """https://easings.net/#easeInOutElastic"""
+    c = 2 * pi / 4.5
+    if 0 < x < 0.5:
+        return -(pow(2, 20 * x - 10) * sin((20 * x - 11.125) * c)) / 2
+    elif 0.5 <= x < 1:
+        return (pow(2, -20 * x + 10) * sin((20 * x - 11.125) * c)) / 2 + 1
+    else:
+        return x    # x in (0, 1)
+
+
+def out_elastic(x):
+    """https://easings.net/#easeInOutElastic"""
+    c = 2 * pi / 4.5
+    if 0 < x < 0.5:
+        return -(pow(2, 20 * x - 10) * sin((20 * x - 11.125) * c)) / 2
+    elif 0.5 <= x < 1:
+        return (pow(2, -20 * x + 10) * sin((20 * x - 11.125) * c)) / 2 + 1
+    else:
+        return x    # x in (0, 1)
+
+
 # https://easings.net/
 EASING = {
     "none": lambda x: 1.0,
     "round": lambda x: 0.0 if x < 0.5 else 1.0,
     "linear": lambda x: x,
+    "in_sine": lambda x: 1 - cos((x * pi) / 2),
+    "in_out_sine": lambda x: -(cos(x * pi) - 1) / 2,
+    "out_sine": lambda x: sin((x * pi) / 2),
+    "in_quad": lambda x: x * x,
+    "in_out_quad": lambda x: 2 * x * x if x < 0.5 else 1 - pow(-2 * x + 2, 2) / 2,
+    "out_quad": lambda x: 1 - pow(1 - x, 2),
     "in_cubic": lambda x: x * x * x,
     "in_out_cubic": lambda x: 4 * x * x * x if x < 0.5 else 1 - pow(-2 * x + 2, 3) / 2,
     "out_cubic": lambda x: 1 - pow(1 - x, 3),
+    "in_quart": lambda x: pow(x, 4),
+    "in_out_quart": lambda x: 8 * pow(x, 4) if x < 0.5 else 1 - pow(-2 * x + 2, 4) / 2,
+    "out_quart": lambda x: 1 - pow(1 - x, 4),
+    "in_quint": lambda x: pow(x, 5),
+    "in_out_quint": lambda x: 16 * pow(x, 5) if x < 0.5 else 1 - pow(-2 * x + 2, 5) / 2,
+    "out_quint": lambda x: 1 - pow(1 - x, 5),
+    "in_expo": lambda x: pow(2, 10 * x - 10) if x else 0,
+    "in_out_expo": in_out_expo,
+    "out_expo": lambda x: 1 - pow(2, -10 * x) if x != 1 else 1,
+    "in_circ": lambda x: 1 - sqrt(1 - pow(x, 2)),
+    "in_out_circ": in_out_circ,
+    "out_circ": lambda x: sqrt(1 - pow(x - 1, 2)),
+    "in_back": lambda x: 2.70158 * pow(x, 3) - 1.70158 * pow(x, 2),
+    "in_out_back": in_out_back,
+    "out_back": lambda x: 1 + 2.70158 * pow(x - 1, 3) + 1.70158 * pow(x - 1, 2),
+    "in_elastic": in_elastic,
+    "in_out_elastic": in_out_elastic,
+    "out_elastic": out_elastic,
 }
 
 DEFAULT_EASING = "in_out_cubic"