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[mathlib] Clean up AngleVectors comments a little 

They're still slightly confusing, but the situation itself is confusing,
but the comments should be a little more helpful now as they are more
explicit about the orientation of the matrices and just which axis
points where.
This commit is contained in:
Bill Currie 2022-03-14 11:51:50 +09:00
parent ef850d97ea
commit 16440bce2d
1 changed files with 18 additions and 11 deletions
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29
libs/util/mathlib.c
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@ -504,13 +504,21 @@ BoxOnPlaneSide (const vec3_t emins, const vec3_t emaxs, plane_t *p)
#endif
/*
angles is a left(?) handed system: 'pitch yaw roll' with x (pitch) axis to
the right, y (yaw) axis up and z (roll) axis forward.
angles is a left handed system: 'pitch yaw roll' with x (pitch) axis to
the right, y (yaw) axis up and z (roll) axis forward. However, the
rotations themselves are right-handed in that they follow the right-hand
rule for the world axes: pitch around +y, yaw around +z, and roll around
+x.
The math in AngleVectors has the entity frame as left handed with x
(forward) axis forward, y (right) axis to the right and z (up) up. However,
the world is a right handed system with x forward, y to the left and
z up, thus the negation for right.
This results in the entity frame having forward pointed along the world +x
axis, right along the world -y axis, and up along the world +z axis.
Whether this means the entity frame is left-handed depends on whether
forward is local X and right is local Y (left handed), or forward is local
Y and right is local X (right handed).
NOTE: these matrices have forward, left and up vectors horizontal rather
than vertical and are thus the inverse of the matrices to produce the
actual rotation.
pitch =
cp 0 -sp
@ -551,11 +559,10 @@ AngleVectors (const vec3_t angles, vec3_t forward, vec3_t right, vec3_t up)
forward[0] = cp * cy;
forward[1] = cp * sy;
forward[2] = -sp;
// need to flip right because it's a left handed system in a right handed
// world
right[0] = -1 * (sr * sp * cy + cr * -sy);
right[1] = -1 * (sr * sp * sy + cr * cy);
right[2] = -1 * (sr * cp);
// need to flip right because the trig produces +Y but right is -Y
right[0] = -(sr * sp * cy + cr * -sy);
right[1] = -(sr * sp * sy + cr * cy);
right[2] = -(sr * cp);
up[0] = (cr * sp * cy + -sr * -sy);
up[1] = (cr * sp * sy + -sr * cy);
up[2] = cr * cp;