From fc175dbb72f80764431c1fe82ab8996b114831da Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sat, 4 Feb 2023 11:07:21 -0800
Subject: Add slerp and qslerp.

---
 test/vec3_test.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 test/vec3_test.c

(limited to 'test/vec3_test.c')

diff --git a/test/vec3_test.c b/test/vec3_test.c
new file mode 100644
index 0000000..886fee3
--- /dev/null
+++ b/test/vec3_test.c
@@ -0,0 +1,68 @@
+#include <math/vec3.h>
+
+#include <math/float.h>
+
+#include "test.h"
+
+#include <stdio.h>
+
+static const float eps = 1e-7;
+
+static inline void print_vec3(vec3 v) {
+  printf("{ %f, %f, %f }\n", v.x, v.y, v.z);
+}
+
+/// Slerp between two vectors forming an acute angle.
+TEST_CASE(vec3_slerp_acute_angle) {
+  const R angle1 = 0;
+  const R angle2 = PI / 4;
+  const R t      = 0.5;
+
+  const vec3 a = vec3_make(cos(angle1), sin(angle1), 0);
+  const vec3 b = vec3_make(cos(angle2), sin(angle2), 0);
+
+  const vec3 result = vec3_slerp(a, b, t);
+
+  const R    angle3   = lerp(angle1, angle2, t);
+  const vec3 expected = vec3_make(cos(angle3), sin(angle3), 0.0);
+  TEST_TRUE(vec3_eq(result, expected, eps));
+}
+
+/// Slerp between two vectors forming an obtuse angle (negative dot product).
+///
+/// The interpolation must follow the shortest path between both vectors.
+TEST_CASE(vec3_slerp_obtuse_angle) {
+  const R angle1 = 0;
+  const R angle2 = 3 * PI / 4;
+  const R t      = 0.5;
+
+  const vec3 a = vec3_make(cos(angle1), sin(angle1), 0);
+  const vec3 b = vec3_make(cos(angle2), sin(angle2), 0);
+
+  const vec3 result = vec3_slerp(a, b, t);
+
+  const R    angle3   = lerp(angle1, angle2, t);
+  const vec3 expected = vec3_make(cos(angle3), sin(angle3), 0.0);
+  TEST_TRUE(vec3_eq(result, expected, eps));
+}
+
+/// Slerp between two vectors forming a reflex angle.
+///
+/// The interpolation must follow the shortest path between both vectors.
+TEST_CASE(vec3_slerp_reflex_angle) {
+  const R angle1 = 0;
+  const R angle2 = 5 * PI / 4;
+  const R t      = 0.5;
+
+  const vec3 a = vec3_make(cos(angle1), sin(angle1), 0);
+  const vec3 b = vec3_make(cos(angle2), sin(angle2), 0);
+
+  const vec3 result = vec3_slerp(a, b, t);
+
+  // slerp goes from a to b following the shortest path, which is down from a
+  // towards b. The resulting angle is therefore +PI of the angle we get from
+  // lerping the two input angles.
+  const R    angle3   = lerp(angle1, angle2, t) + PI;
+  const vec3 expected = vec3_make(cos(angle3), sin(angle3), 0.0);
+  TEST_TRUE(vec3_eq(result, expected, 1e-5));
+}
-- 
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