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MD5 swizzle

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I just got a Doom 3 MD5 model to render correctly, but i want to have it in XYZ coordinates rather than XZY coordinates. I tried flipping just the vertex positions, but then (of course) the skeleton won't be flipped. Then i tried flipping the quaternion values directly when i read the joints, and i got some really strange result (the model "marine" looks like some scary hellish alien. It could actually have been a real model [grin]). Is there a simple way to do this, like flipping some values, or do i have to re-calculate all quaternions in some "proper" way?

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I managed to figure it out by myself. The secret is to rotate both the quaternion part and the pos part by a 90 degree axis quaternion. Here's the source if anyone should need it:

* Quternion functions from

float posVec[3] = { pos_x, pos_y, pos_z };
float orientQuat[4] = { orient_x, orient_y, orient_z, 0.0f };

// create 90 degree rotation quat
float angle = (-90.0f / 180.0f) * 3.1415f;
float axis[3] = { 1.0f, 0.0f, 0.0f };
float rotQuat[4] = { axis[0] * sin(angle/2), axis[1] * sin(angle/2), axis[2] * sin(angle/2), cos(angle/2) };

// rotate model from z-up to y-up
Quat_rotatePoint(rotQuat, posVec, m->skeleton[jointCounter].pos);
Quat_multQuat(rotQuat, orientQuat, m->skeleton[jointCounter].quat_orient);

void Quat_computeW( quat4_t q )
float t = 1.0f - (q[0] * q[0]) - (q[1] * q[1]) - (q[2] * q[2]);

if( t < 0.0f ) {
q[3] = 0.0f;
else {
q[3] = -sqrt( t );

void Quat_multQuat( const quat4_t qa, const quat4_t qb, quat4_t out )
out[3] = (qa[3] * qb[3]) - (qa[0] * qb[0]) - (qa[1] * qb[1]) - (qa[2] * qb[2]);
out[0] = (qa[3] * qb[0]) + (qa[0] * qb[3]) + (qa[1] * qb[2]) - (qa[2] * qb[1]);
out[1] = (qa[3] * qb[1]) + (qa[1] * qb[3]) + (qa[2] * qb[0]) - (qa[0] * qb[2]);
out[2] = (qa[3] * qb[2]) + (qa[2] * qb[3]) + (qa[0] * qb[1]) - (qa[1] * qb[0]);

void Quat_rotatePoint( const quat4_t q, const vec3_t in, vec3_t out )
quat4_t tmp, inv, final;

inv[0] = -q[0]; inv[1] = -q[1];
inv[2] = -q[2]; inv[3] = q[3];

Quat_normalize( inv );
Quat_multVec( q, in, tmp );
Quat_multQuat( tmp, inv, final );

out[0] = final[0];
out[1] = final[1];
out[2] = final[2];

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