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Old 7th November 2004, 08:35 AM   #1
Malekovits
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Hi everybody !
I 'm sure that most of you have played, or see (a review propably) the new DOOM 3. A magazine for computer games, had a review. The review had some screenshots of the game and one of them shows a monster (like a spider with fliped human head) that walks on a surface like grid (I can't tell it in other words) and its not walking like one object but each of its legs goes on the grid and not in the space of the grid. The magazine does't says anything about it's motions / animations and I am very curious to learn how they make these motions. I am 100% sure that this is not bone animation. Does anyone know how these motins are made? This would very usefull for animation/motion system on AC3D.
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Old 7th November 2004, 02:50 PM   #2
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I'm not quite sure I follow you, but I believe you're talking about "inverse kinematics" (IK). This requires a skeleton (so it would use bones) and some kind of animation data to tweak using an IK solver.

Alternatively, it could be a fully scripted animation with no real magic behind it at all.

--Jeff
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Old 7th November 2004, 04:56 PM   #3
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Thank's for the reply! But what is this "inverse kinematics" and what do you mean "data to tweak using an IK solver" (what is solver?)?
Also, any program that has IK ?
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Old 7th November 2004, 06:17 PM   #4
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first, it is done with "bones" -- just a system of setting up individual matrices for specific parts of the body(model).
second, you move/tweak the matrices to there next saved position(most commonly called keyframes).

imagine a person walking, every second you "snap shot" his postion(remeber every postion of every major part of his body), until he has taken a full two steps, then save the data.
now pretend you can move/tween his parts between every snap shot, in sequence.
yea, thats basically the idea, it of course is a lot more complicated to acculy do it in code.

hope that helps.
--Philip
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Old 7th November 2004, 06:38 PM   #5
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I know about bone animation (not the "advanced" I suppose that there are). Nice idea ! But i have one also: Let' s say that we already have made a monster (like that one in DOOM 3 )and it's bone animation. When each of it's legs, the edge (vertices) goes near the grid, not in the space, automaticaly snap in the grid. I can't say it better with words but if I knew how to put an image over here it would be diferent.
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Old 7th November 2004, 07:00 PM   #6
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im not quite getting what your trying to say. :?

but to post images you have to first find a web host that you can up load your images to.
http://photobucket.com/ is the best ive found for this.
then just post the URL's they give you.
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Old 7th November 2004, 07:50 PM   #7
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IK (short for 'Inverse Kinematics'). When you take a skeleton and you create a 'reaching' animation by moving the shoulder, then the elbow, then the forearm, then you are doing 'forward kinematics'. If you were to grab the hand and 'pull' the whole skeleton to reach an object, then you are doing 'inverse kinematics'.

An IK solver takes a point in space that you want a given bone to reach and then adjusts the bones so that you get what you asked for. IK is most easily done during authoring, but it is most *interesting* when done at runtime.

Blender had IK the last time I checked. I don't remember how well it was supported, though. I have not touched that product in many years. That was an authoring-time solution, though, and would not adapt to the environment like what you are wanting. Do a search on 'inverse kinematics algorithms' and you'll probably turn up something like what you want.

-- Jeff
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Old 8th November 2004, 03:31 AM   #8
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Hi,

don't think of bone-animation as a MD2 like keyframe animation, only. That is used very often since modelling with bones is easier, and interpolation keyframes is faster. However, the HalfLife game had a level, where you had to climb down a tube, and in the middle there was a one armed plant thingy, that could hear you and attack where there was a lud sound. You cannot do this with keyframe animation - it's bones, that are moved towards the sound position. All the child-bone's positions have to be calculatied according to their length and linkage to the moved bone. That's a very high CPU loading process. I bet DOOM3 uses a pre-calculated version for speed reasons, but I'm not sure.
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Old 8th November 2004, 05:13 PM   #9
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Thank's for your explaination Thaellin. I have get an idea about whow IK works. I thing that AC3D must have IK. Except from blender, any other programs that have IK? Does 3d studio?
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Old 8th November 2004, 05:57 PM   #10
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I'm pretty sure Maya and 3DStudioMAX have IK solvers, but when you are doing this at content-creation time, you will not see the results that you get if you're doing it in the game at runtime.

IK is a convenient way to create some animations during content-creation time. For some effects, though, it is the only efficient way to create them at runtime. Actually placing a character's feet on a sloped terrain or staircase, for example, might be best done using runtime IK.

Runtime IK is not something any content creation program can help you with - you need to modify the game engine to support it and to know when to use it.

IK would make AC3D a better product, but basic animation support is definitely the first step.
-- Jeff
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