By Colin 'Chilli' Semple

The basic goal of skinning is to place UV mapping coordinates onto each face of your 3D model, these coordinates should exactly correspond to distinct areas of a 2D bitmap image.  The bitmap gets applied as a material to the object such that the 2D areas cover the 3D faces of the model.  The bitmap can then be painted in any paint package to surface skin which adds detail and realism to the model.

I use the MAX naming convention so...  three vertices are joined together by three edges to form a face.  A number of attached faces forms a polygon or poly.

Most if not all of ChilliSkinner's functions work independently so for example you can mix and match manual and ChilliSkinner steps at any time, the only exception to this is Attach Polys.

Thanks to Black Panther for the kewl Ak47 model.

Your model should be a single mesh although not necessarily a contiguous mesh.

You should check that your model has no isolated vertices, duplicate vertices (often these can be created if you used compound Boolean operations) or incomplete faces.  Sometimes these geometry inconsistencies can be very difficult to spot.

For example if you create a standard MAX 'cone' object with a pointed end you'll find that instead of a single vertex at the tip, you'll have something like 18 vertices on exactly the same spot.  Another good example is the MAX teapot, the lid is created with a number of incomplete faces, just edges.  Both of these examples will cause problems when skinning.

It's a good general rule before you begin to skin your model to select all the vertices on your model and attempt a 'Weld All' operation (either in MAX or with ChilliSkinner) with a low (0.1)  tolerance, if you get a 'No Vertices To Weld' error then that means your model is in good shape as far as duplicate vertices are concerned, if you don't get the error then you had a problem but it should now be fixed.

Step 2 - Break Up Your Model
Break the model up into separate groups of faces (polys).  These polys are the areas of your 3D model that will be laid out flat and will go on to form the paint-able areas on the 2D bitmap.  Objectives here are to end up with a) polys that will be recognisable when you come to paint them  b) polys that are sensibly orientated to make the painting easier c) polys that have minimal or no face distortion d) visible 'seams' (where two polys join) are kept to a minimum.

Manual:
Go round the model selecting groups of faces and detaching them as separate objects.  You should also manually rename each poly you detach using some convention that you will remember later.

ChilliSkinner:

Click 'Auto Detach' which automatically finds and detaches face groups based on a 'Detach Angle' set by the user.

Step 3 - Perfectly Legal Cloning
Once you're happy with the detached polys you need to make a copy or 'clone' of it for later reference.  After cloning you must not make any geometry changes to either the clone or the original.  By geometry changes I mean adding or deleting vertices, faces, edges etc.

Manual:
'Select All' then 'Edit' then 'Clone All'

ChilliSkinner:

Click 'Select All' and then click 'Clone.  ChilliSkinner makes an identical clone but prefixes the cloned polys' names with 'Clone' i.e Object01's clone is named 'CloneObject01'.

Step 4 - Flatten & Arrange
In order for all faces of the model to be given one set of 2D mapping coordinates and to avoid texture/skin distortion every face must be facing the same way and no faces must be hidden or angled so they aren't visible.  There should be no polys overlapping.  At this point it's often useful to rotate, move, scale polys to make the layout more logical, align identical polys, make polys that require more detail larger. 

Manual:
This is a long, tough one...  each detached poly must be manually rotated to face the same way.  Complex polys (none in this example) will need to be manually flattened out or unfolded.  MAX provides no functions to do this easily without distorting the resulting poly afaik.  Then each poly has to be moved around to avoid overlaps between polys.

ChilliSkinner:

Use 'Unfold Polys' and/or 'Flatten Polys' to unfold/flatten the polys.  Use 'Optimise Polys' to rotate polys around so they take up less space or align with each other.  Then use 'Arrange Polys' to lay the polys out in the shape of a square or rectangle.

Step 5 - Attach The Flat Polys
From the separate polys we now need to create a single object again so we must attach them together, but in a set order.

Manual:
Again, a real pain.  You must manually select each poly as you attach them together.  You also need to do it in a re-creatable order i.e. you should attach object 1 to object 2 to object 3 etc.  This is where it's best to use the names you gave each detached poly in step 2.

ChilliSkinner:

Select all polys and click 'Attach Polys'.  ChilliSkinner takes care of attaching the polys in the correct order.

Step 6 - Apply The UV Mapping Coordinates
Once you have all the polys laid out flat you can apply the mapping coordinates.

Manual:
Apply a standard MAX UVW Mapping modifier, use 'Planar', 'View Align' and 'Region Fit' options.

ChilliSkinner:

Click 'Apply Planar Map'.

Step 7 - Attach The 3D Polys
We now need to attach all the separate polys on the 3D clone copy of our model to create a single object again.  They have to be attached in exactly the same order as those in the flattened model.

Manual:
Even more of a pain.  You must manually select each poly as you attach them together in the same way and in exactly the same order as step 5.

ChilliSkinner:

Bring the clone back by clicking 'Toggle Visible', then click  'Select All' and click 'Attach Polys'.

Step 8 - Mighty Morphin'
We now have a flattened version of our model with mapping coordinates and a 3D clone version of our model without the coordinates.  Here we use MAX's Morph function to make the flattened 2D version of our model back into a 3D version again using the 3D clone model as a template.  After morphing, the new 3D object (previously flat) retains the mapping coordinates given to it.

Manual:
Unhide all objects and select the flat object as the morph source, select the 3D object as the morph target and morph them together.

ChilliSkinner:

Click 'Unhide All'.  Click and select the flat object, click and select the 3D object then click 'Morph'.

Step 9 - Weld Everything Back Together
Although the previously flat object is now a 3D model again, it is still comprised of separate polys that are positioned very close to each other.  We now need to join these separate polys together again to re-create our original model perfectly.

Manual:
Drop to sub-object vertex level, select all the vertices and click 'Weld Selected'.

ChilliSkinner:

Just select your model and click 'Weld All'.

There are a number of ways to generate this bitmap but one of the best is to get hold of a MAX plugin called Texporter.  This will create the bitmap for you.

In MAX's Material Editor, select a new material and at the bottom under it's 'Maps' rollout, check the 'Diffuse' checkbox and click the 'Map' button on the right of it  Choose 'Bitmap' as the map type and browse and select the bitmap you just saved from the previous step.  Now drag and drop the new material on top of your object.

Note which part of the bitmap goes onto which face of the model.

Now you can paint your bitmap in Photoshop, Paint Shop Pro or your favourite paint package to get it exactly as you want it.