From 9c75ea795dec316cfa2c33c237ec5bb44c813f6f Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Wed, 17 Jul 2024 17:41:47 +0530
Subject: [PATCH] Recognize more linear bezier curves

---
 kitty/animation.c      | 12 +++++++++++-
 kitty_tests/options.py | 13 +++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/kitty/animation.c b/kitty/animation.c
index 8f8a40e26..f90775b80 100644
--- a/kitty/animation.c
+++ b/kitty/animation.c
@@ -194,10 +194,20 @@ init_function(Animation *a, double y_at_start, double y_at_end, easing_curve cur
     return f;
 }
 
+static bool
+is_bezier_linear(double p1x, double p1y, double p2x, double p2y) {
+    return (
+        (p1x == 0 && p1y == 0 && p2x == 1 && p2y == 1) ||
+        (p1x == 0 && p1y == 0 && p2x == 0 && p2y == 0) ||
+        (p1x == 1 && p1y == 1 && p2x == 1 && p2y == 1) ||
+        (p1x != 0 && p2x != 0 && p1y != 0 && p2y != 0 && p1y / p1x == p2y / p2x)
+    );
+}
+
 void
 add_cubic_bezier_animation(Animation *a, double y_at_start, double y_at_end, double p1x, double p1y, double p2x, double p2y) {
     p1x = unit_value(p1x); p2x = unit_value(p2x);
-    if (p1x == 0 && p1y == 0 && p2x == 1 && p2y == 1) {
+    if (is_bezier_linear(p1x, p1y, p2x, p2y)) {
         init_function(a, y_at_start, y_at_end, identity_easing_curve);
         return;
     }
diff --git a/kitty_tests/options.py b/kitty_tests/options.py
index 5a7700cce..43a5bd206 100644
--- a/kitty_tests/options.py
+++ b/kitty_tests/options.py
@@ -157,16 +157,21 @@ class TestConfParsing(BaseTest):
         cb('linear(0, 0.25 25% 75%, 1)', first=EasingFunction('linear', linear_x=(0.0, 0.25, 0.75, 1.0), linear_y=(0, 0.25, 0.25, 1.0)))
 
         # test that easing functions give expected values
-        def ef(spec, tests, duration=0.5):
+        def ef(spec, tests, duration=0.5, accuracy=0):
             cfv = p('cursor_blink_interval ' + spec).cursor_blink_interval
             self.set_options({'cursor_blink_interval': cfv})
             for t, expected in tests.items():
                 actual = test_cursor_blink_easing_function(t, duration)
-                self.ae(expected, actual, f'Failed for {spec=} with {t=}: {expected} != {actual}')
+                if abs(actual - expected) > accuracy:
+                    self.ae(expected, actual, f'Failed for {spec=} with {t=}: {expected} != {actual}')
 
         ef('linear(0, 0.25 25% 75%, 1)', {0: 0, 0.25: 0.25, 0.3: 0.25, 0.75: 0.25, 1:1})
-        for spec in ('linear', 'linear(0, 1)'):
-            ef(spec, {0: 0, 1: 1, 0.1234: 0.1234, 0.6453: 0.6453})
+        linear_vals = {0: 0, 1: 1, 0.1234: 0.1234, 0.6453: 0.6453}
+        for spec in ('linear', 'linear(0, 1)', 'cubic-bezier(0, 0, 1, 1)', 'cubic-bezier(0.2, 0.2, 0.7, 0.7)'):
+            ef(spec, linear_vals)
+        # test an almost linear function to test cubic bezier implementation
+        ef('cubic-bezier(0.2, 0.2, 0.7, 0.71)', linear_vals, accuracy=0.01)
+        ef('cubic-bezier(0.23, 0.2, 0.7, 0.71)', linear_vals, accuracy=0.01)
 
         ef('steps(5)', {0: 0, 0.1: 0, 0.3: 0.2, 0.9:0.8})
         ef('steps(5, start)', {0: 0.2, 0.1: 0.2, 0.3: 0.4, 0.9:1})