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Fix slerp #26

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Fix slerp #26

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a885c68
Fix slerp
bangbangsheshotmedown Aug 8, 2025
d1d32e0
Keep same arg name
bangbangsheshotmedown Aug 8, 2025
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37 changes: 21 additions & 16 deletions src/exengine/math/mathlib.h
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Original file line number Diff line number Diff line change
Expand Up @@ -604,34 +604,39 @@ static inline void quat_lerp(quat q, quat a, quat b, float weight)

static inline void quat_slerp(quat q, quat a, quat b, float weight)
{
float dot = quat_inner_product(b, a);

quat a2 = {a[0], a[1], a[2], a[3]};

if (dot < 0) {
quat_scale(a2, a, -1);
float dot = quat_inner_product(a, b);

if (dot < 0.0f) {
dot = -dot;
quat tmp;
quat_scale(tmp, a, -1.0f);
memcpy(a, tmp, sizeof(quat));
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This line modifies what seems to be an input variable. Is this intentional?

}

if (dot > DOT_THRESHOLD) {
quat_lerp(q, a2, b, weight);
quat_lerp(q, a, b, weight);
quat_norm(q, q);
return;
}

dot = MIN(MAX(dot, -1.0f), 1.0f);
float theta_0 = acosf(dot);
float theta = theta_0 * weight;

float theta = acos(dot) * weight;
float sin_theta = sinf(theta);
float sin_theta_0 = sinf(theta_0);

quat c;
quat_scale(c, a2, dot);
quat_sub(c, b, c);
quat_norm(c, c);
float s0 = cosf(theta) - dot * sin_theta / sin_theta_0;
float s1 = sin_theta / sin_theta_0;

quat_scale(a2, a2, cos(theta));
quat_scale(c, c, sin(theta));
quat_add(q, a, c);
quat q0, q1;
quat_scale(q0, a, s0);
quat_scale(q1, b, s1);
quat_add(q, q0, q1);
quat_norm(q, q);
}


#include <float.h>
static inline void mat4x4_rotate_quat(mat4x4 mat, quat q) {
float qxx = q[0] * q[0];
Expand Down Expand Up @@ -728,4 +733,4 @@ static inline void quat_from_mat4x4(quat q, mat4x4 M)
q[3] = (M[p[2]][p[1]] - M[p[1]][p[2]])/(2.f*r);
}

#endif // EX_MATHLIB_H
#endif // EX_MATHLIB_H