[isugamedev-devel] 3D aster code

[Kevin M. <ke...@vr...>]

Hi, 

some guys were asking me after the club about my example app "aster".  
I don't think I caught their names, so hopefully they are on the list...

anyway, I was talking to Josh about how to do the rotations in 3D using 
sin/cos as aster currently does it.  If matrices scare you, then I have a 
much easier way for you:

first, aster kept track of ship rotation using [theta].
since you want to include pitch (rotation about x axis), then you'll want 
another rotation variable, lets call it [phi].  you manipulate this var to 
control your ship's pitch.

ok, so [theta] is rotation about Y axis, and [phi] is rotation about X 
axis.  

then for each one, calculate your heading.  for [theta] we did this 
according to what we've learned in trig class:

// get the forward vector of ship in the XZ plane
yaw_vector_x = cos( deg2rad( theta + 90 ) );
yaw_vector_y = sin( deg2rad( theta + 90 ) );

well, for [phi[, you'll do something very similar...

// get the forward vector of ship in the ZY plane
pitch_vector_z = cos( phi + 180 );
pitch_vector_y = sin( phi + 180 );

that 180 might be off, so you may want to play with it.


THEN... you'll simply add the vectors to get your ship's forward vector:

shipForward[0] = yaw_vector_x;
shipForward[1] = yaw_vector_y + pitch_vector_y;
shipForward[2] = pitch_vector_z;

then you should normalize this vector:
norm( shipForward )

now the length is 1.0 instead of 2.0...




hope this works, I haven't tried it but the math looks right...

-- 
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Kevin Meinert                                  __  _   __  
http://www.vrac.iastate.edu/~kevn         \  ||  \| \ /  ` 
Virtual Reality Applications Center        \ ||.-'|--\\    
Howe Hall, Iowa State University, Ames Iowa \||  \|   \`__,
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