Negative Volume Part Creation Guide for DoGa L3
====

Negative volume parts are parts that allow the modeller to cut a 'hole' in existing parts that are the shape of the negative volume part. As with
all DoGa parts these parts can be scaled and textured if created correctly and are very useful for modifying more generic parts to a specific 
purpose. 

There are two different methods of creating negative volume parts for DoGa. Both are equally effective and have similar end uses. The first
method only requires DoGa and a text editor while the second method requires a secondary program such as MetaSequoia. The first method is
typically used to take an existing part and make it partially or completely into a negative volume part. This is useful for turning something
like an existing nozzle part into a recessed nozzle or duct for instance. The second method is generally used to make a more custom part to meet
a specific purpose. It also has the advantage in that it can be used to create negative volume parts that will clip to an existing surface and 
will thusly be flush with the modified part. These parts could be used to add missile tubes or gun ports to an existing model without building up
large numbers of parts thus cutting down on the number of polygons used and decreasing render time.

====

The First Method:

In this example we will use a cylinder as the sample part. You can use nearly anything as long as it has some thickness to the walls but a
cylinder is one of the most useful shapes so we'll start with that.

Take a double walled cyclinder first and size it appropriately. Cap one end with a plane or other part then duplicate both parts and position 
them one on top of the other. It's important that they be exactly on top of each other. Be careful not to use the 'duplicate front and back' or
either of the other mirroring functions as it is important that all the points and lines be right on top of each other. 

Place a circular plane just above the end of the open cyclinder so that it is not touching the open end but is only slightly above it. Make sure 
it is spaced to overlap the inner cylinder wall but not the outer cylinder wall. This should be the last step done in DoGa so as to make the 
rest of the steps easier.

Export the whole thing as a part then open the .atr file associated with whatever you named the part. Erase everything and replace it with the 
following:

atr edgecancel {
	tra ( 1.0 )
	opt ( edgecancel )
}
atr supertrans
{
	tra ( 2 )
}
atr BodyD
{
	col ( rgb ( 0.65 0.65 0.65 ) )
	opt ( nocastshadow )
}

Save the file and then open the .suf file associated with whatever you named the part and search for every segment labelled 'atr'. This will 
usually be followed by "BodyM__noname". Shorten this to just BodyM, no "'s. There will usually be 5 atr segments and for the last one you want 
to change it from "BodyM__noname" to supertrans. As long as you added the 'floating cap' as the last part before exporting this will be the last 
atr segment every time. Save it and give it a try. 

====

The Second Method:

This example is notably more complex and will require some skill with a secondary program capable of exporting parts in .SUF format. Again we 
will use a cylinder as the example part.

The first step is to create a 

====

What are those atr's and what do they do?

Atr's are part attributes. They are somewhat similar to the materials you apply to parts when you model but they cover a wider range of both
the materials and special attributes for each polygon as well. 

The first attribute listed, edgecancel, does not actually cancel an edge but instead makes it so you 'see' the various edges in the preview 
window before you render. These cancelled edges will appear as white instead of black lines in the renderer window. The second attribute is the 
most important for our purposes: supertrans. Supertrans is literally super-transparent. It cuts right through the next few polygons as the model
is rendered. You can modify this by changing the 'tra' option though do it with care! If you reduce this to 1 it will only cut through the first
polygon the supertrans property is applied to. Since supertrans is applied to a polygon already it will then only cancel that specific polygon. 
Useful if you want an object with a number of holes in it. At two it will cut through both it's own polygon and the next one it encounters. This 
is generally enough to do the job as generally a negative volume will only be applied to a single part or plane of a part. You can increase this
for very custom parts that you might want to have cut through absolutely everything for whatever reason - a cut-away of a model for instance. 

The last attribute is a material attribute. It sets the color of the polygons via the 'col' sub-attribute. In this case that's RGB (Red/Green/
Blue) with the listed percentages. It then also sets any number of the normal material flags such as nocastshadow - meaning the part will not
cast a shadow when rendering. If you consult the list of material attributes in the part file converter you will notice a number of 'BodyX'
attributes. These attributes will allow textures and additional coloring to be laid down on top of them. Other attributes might set the part
to a specific color and not allow texturing. In most cases you never want to use anything but the 'BodyX' attributes for any polygons, even if
you have a specific purpose in mind. Otherwise you may have to go back and change that attribute later on. It's like painting a LEGO block - you 
never know when you might want that block for a different model.

----

Written by Sunset,
Researched by Scolo & Sunset

Contact either of us on irc.gamesurge.net, #nationstates.