The new 'Unfold Poly' function in ChilliSkinner is one of its most powerful features, however if you don't understand the rules by which it works you won't be able to exploit its power. This tutorial attempts to show some basic concepts which hopefully will help you to understand how the 'Unfold Poly' routine works.This tutorial is only for those who want to really decide themselves how to break their models up. 'Unfold Polys' is not an automated function, you need to make decisions and intervene manually to detach the bits of your model to be unfolded by 'Unfold Polys'. If you don't want to do this simply use 'Find & Detach Polys' to do the detaching for you. But the results won't be as nice ;)
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A |
| Look at the picture of a box object created in MAX. You can see that each 'side' or polygon of the box is constructed from two triangular faces. So on this object we have 6 polys and therefore 6x2=12 faces.
Note: I use the MAX naming convention for these tutorials so... three vertices are joined together by edges to form a face. A number of attached faces form a polygon or poly.
At each corner of a face and where faces are joined there is a vertex, shown in the diagram as a red dot. In this example all faces share common vertices with other faces. You can see that in total this object has 8 vertices (one is
hidden in the picture).
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B |
| Now let's 'detach' poly 2 from the box object. I've shown it moved away from the main box for the sake of clarity but in reality when you detach a face it retains its original position.
You will see that the detached poly (2 faces) has its own vertices, the green dots. These vertices were newly created by MAX during the detach process. Notice that the box object still has 8 vertices as before (red dots).
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C |
| Now we do exactly the same with poly 3. Again notice that the original box object, although now missing 2 polys (4 faces), still has 8 vertices.
We now have 3 objects in the scene.
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D |
| Same again, we detach poly 4, the one on the left-hand side facing away from us. You can see 2 of its vertices marked as blue dots.
The box object now has 3 polys (6 faces) and still 8 vertices. The three detached objects (poly 2, 3 & 4) each have 1 poly (2 faces) and 4 vertices.
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E |
| Now it gets a little bit more complicated... imagine if we 're-attach' the 3 separate sides back into position on the original box. Attaching in MAX doesn't automatically join (weld) vertices back together so although we now have only one object (6 polys, 12 faces) again, polys 2, 3 & 4 still have 4 vertices each in addition to the original 8 vertices of our box object.
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F |
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The way in which 'Unfold Polys' actually unfolds polys is determined by how the vertices of adjacent faces are joined or not joined to each other.
In this example we can weld the vertices at the four corners of poly 1. Shown in the diagram as the large red dots, this is where there were 2 (at the bottom) or 3 (at the top) vertices in exactly the same position, we've now 'welded' them together to make a single vertex at each of these points.
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G |
| Now when we run 'Unfold Poly' on the box object it is able to unfold the polys of the object and we end up with the flat object shown. If your visual-spatial reasoning is good you can see that the flat shape can be folded back up to form the box object.
This is the basic rule of 'Unfold Poly'... if the poly could physically be unfolded and laid out flat then 'Unfold Poly' can unfold the poly.
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H |
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| Here are some examples of what can't be unfolded by 'Unfold Polys'
Example 1
Here the triangular face on the right-hand side is only attached by one vertex, 'Unfold Poly' requires polys to be joined by two vertices in order for the poly to be unfolded correctly. |
I |
| To get around this problem the only way would be to make the single object into two separate objects.
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J |
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| Example 2
Here unfolding is not possible without distortion of one or more faces. Visualize the two square sides folded flat and you will see that the triangular face at the top would be stretched until it disappeared.
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| This could be solved by splitting the vertex at top left or top right (as shown) into two vertices... then the triangular face could be unfolded upwards.
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L |
| Like so...
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| Example 3
Here we have the box object without the top or bottom polys. Logically, if this were a real physical object, it couldn't be laid out flat without first making a break vertically somewhere along its circumference.
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| This applies equally to CSv2's 'Unfold Poly' routine, two vertices where a side poly meets another side poly would have to be split into two (the green dots) to enable 'Unfold Poly' to unfold it and create a long flat rectangle.
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O |
| Like so...
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P |
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Hopefully, by now you are saying to yourself: 'OK I understand the theory, now show me how to do it in MAX' in which case you should click here
OR
'Hey... I don't understand something here...?' in which case you should drop me a quick email and I'll do my very best to help you.
If you think this tutorial could be better or you spot a mistake please drop me a quick email with your comments.
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