/* http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/glu/lookat.html
http://msdn.microsoft.com/en-us/library/bb205343.aspx
*/
void
RMtx4LookAtRH( RMtx4* out, const RVec3* eye, const RVec3* at, const RVec3* up )
{
#define AX(i) RVec3GetElement( &axis_x, i )
#define AY(i) RVec3GetElement( &axis_y, i )
#define AZ(i) RVec3GetElement( &axis_z, i )
RVec3 axis_x, axis_y, axis_z;
RMtx4Identity( out );
RVec3Sub( &axis_z, eye, at );
RVec3Normalize( &axis_z, &axis_z );
RVec3Cross( &axis_x, up, &axis_z );
RVec3Normalize( &axis_x, &axis_x );
RVec3Cross( &axis_y, &axis_z, &axis_x );
SET_ELEMENT( out, 0, 0, AX(0) );
SET_ELEMENT( out, 0, 1, AX(1) );
SET_ELEMENT( out, 0, 2, AX(2) );
SET_ELEMENT( out, 0, 3, -RVec3Dot(&axis_x, eye) );
SET_ELEMENT( out, 1, 0, AY(0) );
SET_ELEMENT( out, 1, 1, AY(1) );
SET_ELEMENT( out, 1, 2, AY(2) );
SET_ELEMENT( out, 1, 3, -RVec3Dot(&axis_y, eye) );
SET_ELEMENT( out, 2, 0, AZ(0) );
SET_ELEMENT( out, 2, 1, AZ(1) );
SET_ELEMENT( out, 2, 2, AZ(2) );
SET_ELEMENT( out, 2, 3, -RVec3Dot(&axis_z, eye) );
#undef AX
#undef AY
#undef AZ
}
void
RQuatToAxisAngle( const RQuat* in, struct RVec3* axis, rmReal* radian )
{
if ( axis )
{
RVec3 a;
RVec3SetElements( &a, in->x, in->y, in->z );
RVec3Normalize( axis, &a );
}
if ( radian )
{
*radian = 2.0f * rmAcos( in->w );
}
}