From 0a0f53ffda0a609a843372fbf7d854a72df54c22 Mon Sep 17 00:00:00 2001
From: David Rose <david@ddrose.com>
Date: Sun, 23 Jun 2002 00:02:10 +0000
Subject: [PATCH] fix quaternion multiply order

---
 panda/src/linmath/lquaternion_src.I   | 12 ++++++------
 panda/src/linmath/lquaternion_src.cxx |  4 ++--
 panda/src/pgraph/transformState.cxx   |  4 ++--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/panda/src/linmath/lquaternion_src.I b/panda/src/linmath/lquaternion_src.I
index 05054949fe..80a1cc95e0 100644
--- a/panda/src/linmath/lquaternion_src.I
+++ b/panda/src/linmath/lquaternion_src.I
@@ -56,7 +56,7 @@ xform(const FLOATNAME(LVecBase3) &v) const {
   FLOATNAME(LQuaternion) v_quat(0.0f, v[0], v[1], v[2]);
 
   FLOATNAME(LQuaternion) inv(_v.data[0], -_v.data[1], -_v.data[2], -_v.data[3]);
-  v_quat = (*this) * v_quat * inv;
+  v_quat = inv * v_quat * (*this);
 
   return FLOATNAME(LVecBase3)(v_quat[1], v_quat[2], v_quat[3]);
 }
@@ -67,11 +67,11 @@ xform(const FLOATNAME(LVecBase3) &v) const {
 //  Description: actual multiply call (non virtual)
 ////////////////////////////////////////////////////////////////////
 INLINE_LINMATH FLOATNAME(LQuaternion) FLOATNAME(LQuaternion)::
-multiply(const FLOATNAME(LQuaternion)& rhs) const {
-  FLOATTYPE r = (_v.data[0] * rhs._v.data[0]) - (_v.data[1] * rhs._v.data[1]) - (_v.data[2] * rhs._v.data[2]) - (_v.data[3] * rhs._v.data[3]);
-  FLOATTYPE i = (_v.data[1] * rhs._v.data[0]) + (_v.data[0] * rhs._v.data[1]) - (_v.data[3] * rhs._v.data[2]) + (_v.data[2] * rhs._v.data[3]);
-  FLOATTYPE j = (_v.data[2] * rhs._v.data[0]) + (_v.data[3] * rhs._v.data[1]) + (_v.data[0] * rhs._v.data[2]) - (_v.data[1] * rhs._v.data[3]);
-  FLOATTYPE k = (_v.data[3] * rhs._v.data[0]) - (_v.data[2] * rhs._v.data[1]) + (_v.data[1] * rhs._v.data[2]) + (_v.data[0] * rhs._v.data[3]);
+multiply(const FLOATNAME(LQuaternion) &rhs) const {
+  FLOATTYPE r = (rhs._v.v._0 * _v.v._0) - (rhs._v.v._1 * _v.v._1) - (rhs._v.v._2 * _v.v._2) - (rhs._v.v._3 * _v.v._3);
+  FLOATTYPE i = (rhs._v.v._1 * _v.v._0) + (rhs._v.v._0 * _v.v._1) - (rhs._v.v._3 * _v.v._2) + (rhs._v.v._2 * _v.v._3);
+  FLOATTYPE j = (rhs._v.v._2 * _v.v._0) + (rhs._v.v._3 * _v.v._1) + (rhs._v.v._0 * _v.v._2) - (rhs._v.v._1 * _v.v._3);
+  FLOATTYPE k = (rhs._v.v._3 * _v.v._0) - (rhs._v.v._2 * _v.v._1) + (rhs._v.v._1 * _v.v._2) + (rhs._v.v._0 * _v.v._3);
 
   return FLOATNAME(LQuaternion)(r, i , j, k);
 }
diff --git a/panda/src/linmath/lquaternion_src.cxx b/panda/src/linmath/lquaternion_src.cxx
index 400fca176f..9796514e1d 100644
--- a/panda/src/linmath/lquaternion_src.cxx
+++ b/panda/src/linmath/lquaternion_src.cxx
@@ -106,11 +106,11 @@ set_hpr(const FLOATNAME(LVecBase3) &hpr) {
   csincos(a, &s, &c);
   quat_r.set(c, v[0] * s, v[1] * s, v[2] * s);
 
-  (*this) = quat_h * quat_p * quat_r;
+  (*this) = quat_r * quat_p * quat_h;
 
   if (!temp_hpr_fix) {
     // Compute the old, broken hpr.
-    (*this) = invert(quat_r) * quat_h * quat_p;
+    (*this) = quat_p * quat_h * invert(quat_r);
   }
 
 #ifndef NDEBUG
diff --git a/panda/src/pgraph/transformState.cxx b/panda/src/pgraph/transformState.cxx
index eb429c3d3c..2add73f293 100644
--- a/panda/src/pgraph/transformState.cxx
+++ b/panda/src/pgraph/transformState.cxx
@@ -705,7 +705,7 @@ do_compose(const TransformState *other) const {
     float scale = get_uniform_scale();
 
     pos += quat.xform(other->get_pos()) * scale;
-    quat *= other->get_quat();
+    quat = other->get_quat() * quat;
     quat.normalize();
     scale *= other->get_uniform_scale();
 
@@ -768,7 +768,7 @@ do_invert_compose(const TransformState *other) const {
     // Now compose the inverted transform with the other transform.
     if (!other->is_identity()) {
       pos += quat.xform(other->get_pos()) * scale;
-      quat *= other->get_quat();
+      quat = other->get_quat() * quat;
       quat.normalize();
       scale *= other->get_uniform_scale();
     }