# RE: Vertex blending.

```
On 30-Mar-2000 Keith Lucas wrote:
>
>>I think I see what you mean...
>>
>>normalizing the vectors as the final calculation will produce equal vectors,
>>but may produce some distortion at the joints... depending on what you're
>>using
>>the bone system for, it may be ok :) If you're modeling a human (or other
>>bony
>>creature), then the final vector probably SHOULD be longer on more extreme
>>angles.
>
> This is what I thought. I'll have to give it a go. I just didn't want to
> start
> patching up something that might actually be fundamentally broken if you see
> what I mean.
>

it may be fundamentally broken, the exact behavior depends on what you're using
it for... there are also plenty of methods for interpolating between two
vectors, I'm not exactly sure what kind you're doing... *shrug*

v.i = (a.i + b.i)/2;
v.j = (a.j + b.j)/2;
v.k = (a.k + b.k)/2;

that'll provide a symmetric bisection with a magnitude equal to the average of
the two... (if both your vectors are of length 10, then it will be length 10.
if one vector is 10 and another is 30, it will be 20.)

that's just one simple straightforward way, another way is to convert them to
quaternions, sum them, and convert it back to a vector (pretty popular for
handling 3d orientations, like camera facing, air/space craft orientation, etc.)

I think you don't see a lot of general "all purpose" reverse kinematic code...
for the same reason you don't see a lot of all purpose general game code. It's
designed for the application... :)

> I've not actually seen any code for doing any of this. I've seen lots of
> discussions, but nothing that actually has the nitty gritty in it. I can't
> believe it's still so cutting edge that no-one will talk about it in
> detail...
>

normalizing vectors, or reverse kinematics (bone systems) ? vectors are
trivial, and there're plenty of reverse kinematic demos and snippets...

>>Is the generated vector replacing, or supplementing the existing vertices?
>>For
>>visual quality, it should be supplementing I think
>
> It's providing extra ones essentially, on the outsides of bends.
>

then it's supplementing :) If you're simulating like a flexible pipe or
tenticles or something, then you want them normalized, if you're modeling an
enclosed joint (like an elbow), then you want it to extend out some...

-Erik <erik@smluc.org> [http://math.smsu.edu/~br0ke]

The opinions expressed by me are not necessarily opinions. In all
probability, they are random rambling, and to be ignored. Failure to ignore
may result in severe boredom or confusion. Shake well before opening. Keep
Refrigerated.

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