Working on slerp

test/HandmadeMath.cpp

@@ -3,3 +3,89 @@
 #define HANDMADE_MATH_CPP_MODE
 #define HANDMADE_MATH_NO_INLINE
 #include "../HandmadeMath.h"
+
+#ifndef gb_abs
+#define gb_abs(x) ((x) > 0 ? (x) : -(x))
+#endif
+
+#define GB_MATH_TAU_OVER_2   3.14159265358979323846264338327950288f
+#define GB_MATH_TAU_OVER_4   1.570796326794896619231321691639751442f
+#define GB_MATH_TAU_OVER_8   0.785398163397448309615660845819875721f
+
+static float gb_arctan(float a);
+static float gb_arctan2(float y, float x);
+
+float gb_arccos(float a) { return gb_arctan2(HMM_SquareRootF((1.0f + a) * (1.0 - a)), a); }
+
+float
+gb_arctan(float a)
+{
+	float u = a*a;
+	float u2 = u*u;
+	float u3 = u2*u;
+	float u4 = u3*u;
+	float f = 1.0f + 0.33288950512027f*u - 0.08467922817644f*u2 + 0.03252232640125f*u3 - 0.00749305860992f*u4;
+	return a / f;
+}
+
+float
+gb_arctan2(float y, float x)
+{
+	if (gb_abs(x) > gb_abs(y)) {
+		float a = gb_arctan(y / x);
+		if (x > 0.0f)
+			return a;
+		else
+			return y > 0.0f ? a + GB_MATH_TAU_OVER_2 : a - GB_MATH_TAU_OVER_2;
+	}
+	else {
+		float a = gb_arctan(x / y);
+		if (x > 0.0f)
+			return y > 0.0f ? GB_MATH_TAU_OVER_4 - a : -GB_MATH_TAU_OVER_4 - a;
+		else
+			return y > 0.0f ? GB_MATH_TAU_OVER_4 + a : -GB_MATH_TAU_OVER_4 + a;
+	}
+}
+
+int main() {
+
+	hmm_quaternion q1 = { 0,1,0 };
+	hmm_quaternion q2 = { 0,0,0 };
+	hmm_quaternion Result = { 0 };
+	float time = 0.5f;
+
+	hmm_quaternion x, y, z;
+	float cos_theta, angle;
+	float s1, s2, is;
+
+	z = q2;
+	cos_theta = HMM_DotQuat(q1, q2);
+
+	angle = gb_arccos(cos_theta);
+
+	s1 = HMM_SinF(1.0f - time*angle);
+	s2 = HMM_SinF(time*angle);
+	is = 1.0f / HMM_SinF(angle);
+
+	x.X = z.X * s1;
+	x.Y = z.Y * s1;
+	x.Z = z.Z * s1;
+	x.W = z.W * s1;
+
+	y.X = z.X * s2;
+	y.Y = z.Y * s2;
+	y.Z = z.Z * s2;
+	y.W = z.W * s2;
+
+	Result.X = x.X + y.X;
+	Result.Y = x.Y + y.Y;
+	Result.Z = x.Z + y.Z;
+	Result.W = x.W + y.W;
+
+	Result.X = Result.X * is;
+	Result.Y = Result.Y * is;
+	Result.Z = Result.Z * is;
+	Result.W = Result.W * is;
+
+return 0;
+}