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Set Matrix Forward Direction
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fatcoder Offline
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Post: #1
Set Matrix Forward Direction
For some reason I'm struggling with something that should be very simple. I have a Matrix with a position and scale. For my object, I also have a forward vector. I want to set the matrix so that my object faces the same direction as the forward vector. No matter what I try, it seems to affect the scale of the object.

For example, I have set the position of the object to 20, 2, 10. I have set its scale to 1.7. Now I want update the direction every frame to match the forward vector.

So I start with a matrix and position that looks like this.

x {x=1.70000000 y=0.00000000 z=0.00000000}
y {x=0.00000000 y=1.70000000 z=0.00000000}
z {x=0.00000000 y=0.00000000 z=1.70000000}
pos {x=20.00000000 y=2.00000000 z=10.00000000}

I then use the following code to set the direction I want the object to face.

Vec f = Vec(forward.x,0,forward.y);
f.normalize();
matrix.setDir(f, Vec(0,1,0));

In this example, let's say forward is equal to the following.

Vec2 forward = Vec2(0,1);

I then end up with a matrix and position that looks like this.

x {x=0.00000000 y=0.00000000 z=-1.00000000}
y {x=0.00000000 y=1.00000000 z=0.00000000}
z {x=1.00000000 y=0.00000000 z=0.00000000}
pos {x=20.00000000 y=2.00000000 z=10.00000000}

My object now faces the correct direction, but its scale is gone. If I try to set the scale back, then the object no longer faces the correct direction.

Can anyone explain to me how I scale my object and get it to face the correct direction at the same time?
(This post was last modified: 07-24-2010 01:57 AM by fatcoder.)
07-24-2010 01:57 AM
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Driklyn Offline
Member

Post: #2
RE: Set Matrix Forward Direction
I've noticed that the set methods typically seem to reset the matrix. Looks like setDir only resets the scale and not position. You just have to figure out the right combination of methods to call to get what you desire. It can be a pain sometimes. I think this might work for you.

Code:
matrix.setDir(f, Vec(0,1,0)).scale(1.7);
07-24-2010 10:07 AM
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