Fix animation bug

src/math/quaternion.c

@@ -239,16 +239,19 @@ void quatLook(struct Vector3* lookDir, struct Vector3* up, struct Quaternion* ou
 }
 
 void quatLerp(struct Quaternion* a, struct Quaternion* b, float t, struct Quaternion* out) {
-    if (a->x * b->x + a->y * b->y + a->z * b->z + a->w * b->w < 0) {
-        quatNegate(a, a);
-    }
-
     float tInv = 1.0f - t;
 
+    if (quatDot(a, b) < 0) {
+        out->x = tInv * a->x - t * b->x;
+        out->y = tInv * a->y - t * b->y;
+        out->z = tInv * a->z - t * b->z;
+        out->w = tInv * a->w - t * b->w;
+    } else {
         out->x = tInv * a->x + t * b->x;
         out->y = tInv * a->y + t * b->y;
         out->z = tInv * a->z + t * b->z;
         out->w = tInv * a->w + t * b->w;
+    }
 
     quatNormalize(out, out);
 }
@@ -284,3 +287,7 @@ void quatDecompose(struct Quaternion* input, struct Vector3* axis, float* angle)
     axis->z = input->z * magInv;
     *angle = sinf(axisMag) * 2.0f;
 }
+
+float quatDot(struct Quaternion* a, struct Quaternion* b) {
+    return a->x * b->x + a->y * b->y + a->z * b->z + a->w * b->w;
+}

src/math/quaternion.h

@@ -30,4 +30,6 @@ void quatLerp(struct Quaternion* a, struct Quaternion* b, float t, struct Quater
 void quatApplyAngularVelocity(struct Quaternion* input, struct Vector3* w, float timeStep, struct Quaternion* output);
 void quatDecompose(struct Quaternion* input, struct Vector3* axis, float* angle);
 
+float quatDot(struct Quaternion* a, struct Quaternion* b);
+
 #endif

src/sk64/skelatool_animator.c

@@ -118,11 +118,19 @@ void skAnimatorBlendTransform(struct SKAnimationBoneFrame* frame, struct Transfo
         
         vector3AddScaled(&transforms[i].position, &boneTransform.position, weight, &transforms[i].position);
 
+        if (quatDot(&transforms[i].rotation, &boneTransform.rotation) < 0) {
+            transforms[i].rotation.x -= boneTransform.rotation.x * weight;
+            transforms[i].rotation.y -= boneTransform.rotation.y * weight;
+            transforms[i].rotation.z -= boneTransform.rotation.z * weight;
+            transforms[i].rotation.w -= boneTransform.rotation.w * weight;
+        } else {
             transforms[i].rotation.x += boneTransform.rotation.x * weight;
             transforms[i].rotation.y += boneTransform.rotation.y * weight;
             transforms[i].rotation.z += boneTransform.rotation.z * weight;
             transforms[i].rotation.w += boneTransform.rotation.w * weight;
         }
+        
+    }
 }
 
 void skAnimatorReadTransformWithWeight(struct SKAnimator* animator, struct Transform* transforms, float weight) {