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 eye and up vectors from view matrix
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Reply Quoting This MessageEdit Message Vexator    Member since: 5/24/2005  From: Heidelberg, Germany
 Posted - 6/15/2008 1:56:33 PM
how do i extract the eye and up vectors from a view matrix?

thank you!
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Reply Quoting This MessageEdit Message Lord_Evil    Member since: 8/27/2004  From: Ulm, Germany
 Posted - 6/15/2008 2:54:54 PM
assuming the following matrix layout:

m11 m21 m31 m41
m12 m22 m32 m42
m13 m23 m33 m43
m14 m24 m34 m44

You get the up vector from the view matrix like this:

up = (m12, m22, m32)

For the position/eye vector you need the inverse view matrix and then it's
eye = (m41, m42, m43)
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Reply Quoting This MessageEdit Message Vexator    Member since: 5/24/2005  From: Heidelberg, Germany
 Posted - 6/15/2008 3:06:11 PM
mh but position != eye vector, isn't it? in my matrix class, translation is stored in m14, m24, m34. if the camera looks along the negative z-axis, then the up vector should be (0, 1, 0) and the view vector (0, 0, -1), right? with your suggestion, however, the view vector is (0, 0, 0).. any idea what's wrong?
thanks!


[Edited by - Vexator on June 15, 2008 3:06:32 PM]
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Reply Quoting This MessageEdit Message Lord_Evil    Member since: 8/27/2004  From: Ulm, Germany
 Posted - 6/15/2008 5:50:37 PM
No, eye = position of camera. What you talk of is the lookAt vector or the looking direction. The eye-vector (0,0,0) is the default camera position.
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Reply Quoting This MessageEdit Message Vexator    Member since: 5/24/2005  From: Heidelberg, Germany
 Posted - 6/15/2008 6:08:08 PM
ok sry, so what i need then is the lookAt-vector.. how would i get that? m13, m23, m33?

[Edited by - Vexator on June 15, 2008 5:08:33 PM]
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Reply Quoting This MessageEdit Message Lord_Evil    Member since: 8/27/2004  From: Ulm, Germany
 Posted - 6/16/2008 2:37:48 AM
Using the layout I described earlier, yes!
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Reply Quoting This MessageEdit Message Trienco    Member since: 8/23/2001  From: Munich, Germany
 Posted - 6/16/2008 10:41:31 AM
Only problem is that most people say look-at and mean a point (position + view_direction). Getting just the direction from the matrix is simple (as above).
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