Creating Patches

User support for JPatch

Creating Patches

Postby squirrelhavoc » Wed Jun 29, 2005 3:49 pm

Well, I have been playing with the demo models, so now I am ready to learn how to model with JPatch. Right now, I am still confused about what governs whether a patch is made or not. According to the docs, a patch is made from a 3-4-or 5 point "loop" created with more than one spline, am I right? If I click the "Add Point button to create a new spline, then create one. Click it again, and create another, then click it once more, create the final spline, then weld the points at the ends of each spline, hit F5 and nothing happens. After trying different things to see what makes a patch, I am still confused about what determines whether a patch is made or not.

Can anyone shed some light for me?
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Postby sascha » Wed Jun 29, 2005 4:02 pm

The rules about what defines a patch have changed for version 0.4 and the turorials have not been updated yet, sorry for that.
Basically, a 3-sided patch must be made of 3 individual curve-segments, a 4-sided patch of 4 and a 5-sided patch of 5.
This restriction was necessary to prevent so called degenerate patches (that cause troubles when rendering).
Note that it is still possible to create arbitrary topology meshes using hookes and valid 5-sided and 3-sided patches (the resulting models will actually be better and have no creases).
In 0.4 patches now have a front-and a backside, take a look at the Miscellaneous in the 0.4 modeler documentation (in the wiki).
I hope this was helpful, if you have more questions just post them here.
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Postby squirrelhavoc » Wed Jun 29, 2005 11:07 pm

Ok, I think I understand. What you're saying is that each spline in a patch has to be independant, but still connected, right? Is there anything else special about 4 point patches? I have yet to create one. But I will try with the things you told me about.

Thanks!
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Postby sascha » Thu Jun 30, 2005 11:49 am

What you're saying is that each spline in a patch has to be independant, but still connected, right?

Here's a screenshot that shows all valid (left side) and examples of invalid (right side) 3-, 4- and 5-sided patches as recognized by the new patch-finding algorithm:
Image

Is there anything else special about 4 point patches? I have yet to create one. But I will try with the things you told me about.

You'll normally use 4-point patches, they connect smoothly as long as the topology is rectangular. To change the resolution (or detail level) of the mesh you can use hooks.
Inadequatly used 3- or 5-point patches will cause creases in the surface when rendering. However, some topologies require 3- or 5-sided patches (and it is save to use them in that case). 5 sided patches are not found automatically, instead you have to select the 5 corner points and click on the "create 5-pont patch" button.

My suggestion for modeling is:
1) Whenever possible, use 4-sided patches.
2) If needed, use hooks
3) Only if you can't create the desired topology with 4-sided patches and hooks, try using one or more 5-sided patches.
4) If this isn't possible too, use 3-sided patches.
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Postby squirrelhavoc » Thu Jun 30, 2005 1:32 pm

Thank you, now it makes more sense
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Postby squirrelhavoc » Wed Jul 06, 2005 3:41 am

sascha wrote:The rules about what defines a patch have changed for version 0.4...


Just a quick question about the new way things are done. Are old models using the older way of creating patches compatible with the new preview release, or would you have to remodel it?
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Postby sascha » Wed Jul 06, 2005 7:07 am

Currently JPatch 0.4 does only support the "new" way. While it would be possible to add an option to support the "old" way as well (and let the user choose between them), I'm not sure if it is a good idea.
With a little practice, you'll quickly find out how to change an "old" model to be complient to the new patch-finding rules. To be more precise: If a patch is rejected by the new patch-finder, there is something wrong with that patch (and it will cause visible artifacts when rendering). While in sPatch and hamaPatch there was no other way than using degenerate patches, JPatch offers hooks and 5-sided patches. So when using "old" models, you should think about reworking them for JPatch, the results will look much better.

Nevertheless, I think I will add an option to use the old (sPatch compatible) rules, but you should now that this will cause problems when rendering.
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Postby sutabi » Sat Jul 09, 2005 8:24 am

I'd like to second the confusion I am having:

Image

I made that expecting a patch to show after I click the cal patch button, and nothin happened. What am I doing wrong?
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Postby dcuny » Sat Jul 09, 2005 9:04 am

You're assuming that when two splines cross, JPatch will connect them together. That's not the case. Here's an image from an excellent Basic Splinesmanship tutorial:

Image

Note that E and F are the same two splines, with the same number of points - they've just had two control points welded together. (Check out the tutorial link above for more details). Similarly, A and B have the same number of points as C - it's just that C has two of the points welded together.

To connect splines together, you have to "weld" a yellow control point on one spline to a yellow control point on another spline. Do this by dragging one control point close to another control point you want to join it to. Once they are adjacent, keep the left mouse button held down, and also click down with the right mouse button. The points should be welded together.

For more details, check out the tutorial link. (This would be a good thing to have a Wink tutorial about - especially the inevitable "How do I insert points" question ;)).
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Postby sascha » Sat Jul 09, 2005 12:05 pm

Sutabi,

I think David answered your question. If not, feel free to ask!
Note that the patches displayed in the A:M screenshot are not valid in JPatch 0.4 (you need 4 non-continguos curve-segments for a 4-sided patch).

About video or flash tutorials: What I really like about the A:M flash tutorials is the soundtrack: You can see what's going while listening to the explaination. That's much easier that looking at the action and reading what's going on at the same time. (The only thing that's missing is a visual hint about which mousebuttons or keys were pressed).

Unfortunately I'm not a native english speaker, and as you probably can see I'm having difficulties writing in english, so I'm not going to record a tutorial.

Any volunteers (David already lent his voice for two animations :wink: ) ?
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Postby dcuny » Sat Jul 09, 2005 12:27 pm

There's a neat tool called vnc2swf that will record sessions. One of the newer features is that you can add audio tracks to it.

It's not entirely turnkey, but the results look quite nice. You can even attach audio to it. Anyone want to give it a shot? :)
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Postby sascha » Sat Jul 09, 2005 2:00 pm

I've seen a someone using a "vnc proxy" to record vnc sessions, but it required the vncviewer and some hacked scripts to playback. If it can be converted to a standard .swf that would be great! I'll have a look at it.

When recording such videos we should bear in mind that they should playback in a browser window at 1024x768, so the action resolution of the "video" shouldn't be higher than that.
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Postby sutabi » Sat Jul 09, 2005 4:13 pm

Thanks as for tutorials I can make .avi tutorials with camtasia, so once I get the hand of this app Ill sure be happy to make and host one.
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Postby sutabi » Sat Jul 09, 2005 5:38 pm

=_= still having troble here.

Not sure what I am doing wrong here very few patches are made the rest are ignored. Also the auto mirror tool.... it doesn't seem to update, nor connect the center points...
Image
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Postby squirrelhavoc » Tue Jul 26, 2005 1:40 am

sascha wrote:The rules about what defines a patch have changed


Just curious, why did it change? I recently had a chance to try out A:M for a few minutes, and I found modelling a tad easier with the lighter restrictions. I was also surprised at how jpatch was pretty much as complex and robust as A:M in a lot of ways. Good work!
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