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 Author Topic: I'm haveing trouble with some geometry  (Read 2294 times)
Nate_Bro
Newbie

Posts: 31

 « on: January 08, 2008, 02:47:55 pm »

I'm working on a particle system, but I'm haveing trouble with reflections. I have colision detection, but when the particles need to change direction, my formula is not very good.

all i'm doing now is fliping the axis...

like (4,5) == (-4,5)

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My computer specs for Anim8or and other graphics:
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2.  3.0 GHz Pent D 4 MB L2, with ATI 512 MB Vid Card
3.  1.7 GHz Pent Celeron M, with ATI 64 MB Vid Card
Steve
Sr. Member

Posts: 456

 « Reply #1 on: January 11, 2008, 12:20:33 pm »

You need to reflect the incomming vector off the plane of reflection.  Your computation assumes that the plane is x=0.  In general the direction of the outgoing vector is:

Vout = Vin + 2N*Dot(Vin, N)

where N is the plane normal, Vin is the normalized incomming direction and Vout is the outgoing direction,  (You need to normalize Vout after this computation.)

Here is a detailed description.  See equation (3) (but not that the normal is reversed from my formula so the subtract the terms instead of adding them).

http://mathworld.wolfram.com/Reflection.html
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sciwizeh
Newbie

Posts: 22

 « Reply #2 on: January 11, 2008, 05:22:45 pm »

when i read the first post i wasn't sure what you were asking, but now i get it.

had i known i would have said: to make bouncing realistic would require a bit of vector math, i don't know the specifics.

i believe steve has put it in pretty good terms
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Nate_Bro
Newbie

Posts: 31

 « Reply #3 on: January 11, 2008, 05:37:44 pm »

Thank you Steve, that helps a lot! I'm still new to vector math and normals, but I'm slowly learning
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My computer specs for Anim8or and other graphics:
1.  3.2 GHz Pent 4 HT 1 MB L2, with ATI 128 MB Vid Card
2.  3.0 GHz Pent D 4 MB L2, with ATI 512 MB Vid Card
3.  1.7 GHz Pent Celeron M, with ATI 64 MB Vid Card
lppena
Full Member

Posts: 198

Anim8or, does a body good.

 « Reply #4 on: February 07, 2013, 12:24:13 pm »

Thank you Steve, that helps a lot! I'm still new to vector math and normals, but I'm slowly learning

I hear what you're saying about vector math and it's role in 3D modeling software like Anim8or. I wish that someone would post some articles on how Anim8or uses this information to do stuff in Anim8or. Steve, you created a quite awesome product with some very advanced features. I use Anim8or all the time now and seem to grow more fond of it the more that I play with it. Leroy.
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