Overview Page Added

The JPatch Documentation Project has been launched in the Wiki. It's aim is to create a complete, in-depth documentation for JPatch. This forum should be used for discussion related to JPatch's documentation.

Overview Page Added

Postby dcuny » Mon Jan 23, 2006 10:21 am

I started working on a General Overview to Animating with JPatch page. I'm a bit confused with how the Wiki is organized, so I might have put it in the wrong place.

The intent is to give someone who might not be familar with computer animation a general overview of how to use JPatch to do animation. It tries to cover really basic stuff at a conceptual level, like why the timeline shows time using fractional frame amounts, what overshoot is, what FK and IK are, and so on. I've held off on adding graphics, mostly because everything being discussed will look different in the next release.

I suspect this would ultimately be better served by a tutorial, but it's a start anyway.
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Postby sascha » Mon Jan 23, 2006 10:53 am

Cool, thanks a lot!

I'll read through it later today.
I'm a bit confused with how the Wiki is organized, so I might have put it in the wrong place.


Well, the docs: folder contained the "original" documentation that I wrote. Torf started the "JPatch Documentation Project" in parallel, it's in the jdp: folder. I think that eventually the jpd will become the "official" documentation. Feel free to alter the table of contents on the index page.

One thing I noted was some explainatory text about timecodes and frame-numbers. I wander if it really is a good thing to start with frame 1, I've posted my arguments for starting with frame 0 in another thread:
sascha wrote:After some thought, I now tend to support frame numbers starting at 0 instead of 1.

It's obvious that the timecode should start with 00:00:00.0 - that's what we're used from our clocks anyway.

The only reason for starting frame numbers with 1 would be the paradigm that we think of the first frame as frame number 1.
But when designing the ruler, I suddenly had a problem:
It's common to label e.g. every tenth frame - starting from 0 this would be 0, 10, 20,... - but starting from 1 would make this 1, 11, 21,... which looks quite odd.

So I think that frame numbers should start from 0. Computer nerds will have no problem with counting from zero, but there are also a lot of everyday items that start counting from 0: Clocks, rulers, thermometers, game scores, all sorts of counters, just to name a few.
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Postby dcuny » Mon Jan 23, 2006 11:08 am

Yes, I was wondering about that as well. I'll see what other programs use as their defaults. Although it's not good to slavishly following other programs, I think it's a good idea to follow their lead where possible. If JPatch strays too much, I suspect people will recommend beginners stay away from it, to avoid learning bad habits. People used to other software will also avoid it.
    Edit: Blender's frame numbers start with 1. Some feedback from people experienced with other software would be helpful (hint, hint).
I've added a screenshot of the timeline, and a couple to illustrate the morph targets. I think the discussion about overshoot and keys will be much more clear with images of the timeline to accompany it.
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Re: Overview Page Added

Postby Torf » Mon Jan 23, 2006 6:25 pm

dcuny wrote:I started working on a General Overview to Animating with JPatch page.

Cool!

I'm a bit confused with how the Wiki is organized, so I might have put it in the wrong place.

It's a wiki, there's no wrong place :D No, seriously: It seems that outside the JDP the wiki has not much structure (simply because there's not much content). With the JDP, I started the other way round, creating the structure before the content. If you want to add your tour to the JDP (And that would be nice!), I'd insert it as follows:
Code: Select all
Contents
    * Introduction to JPatch
    * Downloading and installing JPatch
    * A quick tour through JPatch and its features
--> insert it here
    * Reference
    * Tutorials
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Postby sascha » Sat Jan 28, 2006 11:30 am

I took another look at the General Overview to Animating with JPatch wiki-page.

I think that the joint in the example with the bending elbow is in the wrong place (the lower arm bone is too short):
Image

From what I've found out, I think it is best to use three segments at the joint, and place the joint in the middle of the center segment.
If the limb is too thik, you can also "rotate" the outer segments (like on the right side):
Image
The image shows the arm after bending, whitout any muscle-morphs (weighting mode is default "soft"). Muscle morph targets could be added for muscle bulges and of course to fix the intersection problem when the elbow is fully bent, but in general this layout yields a good starting point.

You've asked what "Joint rotation" is:
I initially planned to allow an arbitrary axis for each rotation-dof - but this is unneccesary and painful to setup.
So I implemented it this way: A rotation DOF can either be yaw, pitch or roll. Roll is always aligned to the bones axis, yaw and pitch are perpendicular to the bones axis (and to eachother). This doesn't fully determine the exact axes for yaw and pitch though - so a heuristic is used to set them up. If you are not happy with them, you can use the joint-rotation slider to rotate the yaw and pitch axes around the bone (the slider ranges from 0 to 360 degrees). This is not a DOF and it can not be changed during the animation - in fact changing it after a model was rigged will lead to some strange results. It is only meant to determine the axes for the yaw and pitch DOFs and should be set immediately after creating the bone (or these DOFs) and before working on them.
If your model's reference pose is approximately world x/y/z axis aligned (e.g. standing upright, looking into +/- z direction, arms outstretched) you'll most likely don't have to use the "joint rotation" slider.

dcuny wrote: 1. Pitch: Rotation about the x axis.
2. Yaw: Rotation about the y axis
3. Roll: Roation about the z axis

Well, yes and no. I'm not sure if this will lead to confusion. You're right about the axes, but these are the axes in the bone's local coordinate system (which depends on the bones initial orientation and the setting of the joint rotation, and of course the rotation of the parent bones if they are not in their reference position).
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Postby dcuny » Sat Jan 28, 2006 12:26 pm

You're right - the bone is placed in the wrong part of the arm. The example (in itself) is valid; it's would be better to show a good example in the documentation. :)

I've also read that the three segment joint design is best, and I may just filch your graphic. I didn't actually design the arm in the example myself, I was in a hurry and grabbed it off a free A:M model someone had built.

I also agree that describing the three axis is confusing - I've been puzzling over the last couple of days exactly how to describe this correctly. Dropping the x/y/z part of the description is a good idea. I think an image would be best here - I recall one in the original Blender documentation that I especially liked which showed bones with arrows showing the degrees for freedom. It would also be good to include an elbow joint, since that's the classic example of a limited DOF.

Thanks for the feedback! :D
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