Surfacing is the process of applying shading attributes to the 3D geometry in the scene. The various shading attributes will make a surface red and shiny or dull and pitted or any of the millions of variations a surface can posses. Surfacing in MODO uses a layer and mask based metaphor to assign these attributes to a surface. Masks determine the area where the surfacing properties are applied. Within these masks the attributes are defined. This is similar conceptually to how silk-screening works for the garment industry. Take for instance the graphic on the t-shirt you are likely wearing right now. Each color on the shirt requires a new screen (mask!) and when the next color (layer!) is applied it supersedes the previous color where they overlap. Of course transparent ink could be used to allow the other colors to show through - this is the same in MODO too, changing a layers transparency will allow the lower layers to show through, but thats getting a little ahead of ourselves. The screens for the shirt are made by an artist manually drawing them out and going through a complex process that allows ink to flow through only certain areas. A screen or mask in MODO doesn't need to be defined in such a tedious, manual way.
In order to create the mask that confines the surfacing to just the target area, a Polygon Tag will need to be defined. Polygon tags are simply user defined labels associating any number of polygons together as a group. The tag definitions are stored in the geometry itself and can be easily recalled by MODO for a variety of purposes. MODO does have several tag types but the main tag used for surfacing is the 'Material' tag ('Parts' and 'Selection Set' tags are the other types and offer additional functionality for layering materials for different effects, but thats really getting ahead of ourselves). For 'Material' tags, simply defining the tag prompts MODO to create the mask for the surfacing. When tagging geometry for surfacing in this way, the geometry itself determines the shape of the mask, that way when the model moves, so does the mask (with all surfacing going along for the ride as well).
So the important summary here is that MODO surfacing uses a simple mask and layered metaphor for surfacing and tags define the masks that limit that surfacing to the intended areas of the geometry. Lets look at whats involved in applying a tag to a surface-
Assigning Material Tags
In order to assign a tag, you will first need some geometry in the scene. As an example I have created a default 1m sphere.
In 'Polygons' selection mode, select the target polygons you wish to apply the material to, here I have selected the upper half of the sphere. For information on making selections, please reference that page of the documentation.
With the selection active, select the menu bar command "Texture > Assign Material Group" or press the 'm' keyboard shortcut to open the 'Polygon Set Material' dialog box. Here you define the 'Name' of the tag as well as set some basic surfacing attributes. Here I have chosen a red color and named my surface 'Sphere Top'.
Once you have modified the values in the dialogue box to your liking, LMB-clicking the 'OK' button or pressing the 'Return' (Enter) key on the keyboard assign the tag to the selected polygons and defines a material in the 'Shading' viewport. In doing so now, you can see that a tag "
" was added to the Materials panel showing the name that was defined and a new material item "
" has been added to it. If you can't see the material item, click the arrow widget "
" next to the named tag to make it visible. Now any any changes made to this new material item will be limited to only polygons in the scene with the tag 'Sphere Top' (Simply selecting the 'Material' item layer in the Materials panel will displays its associated attributes in the 'Properties' panel for further editing).
You can continue recursively adding additional material tags to define all the various surfaces in a scene in the same way, just remember that a polygon can only have a single Material tag at a time, so if you accidentally assign a second material, it will overwrite the previous value. To fix this, simply select the offending polygon(s) and reassign the previous tag. If you wish to apply complex layering to materials, this requires additional alternative tag types (such as applying a label onto a bottle of wine). Users can define these groupings through the addition of 'Part' tags and 'Selection Sets'.
TIP: In complex scenes, users should consider a strategy for assigning material tags to the various surfaces. Descriptive names are often better than cryptic ones. Consider the case of a car model. One naming scheme might title materials based on their type, such as "Glass", "Rubber", "Leather" and "Chrome", or by what the item itself is; "Windshield", "Tire", "Seat" and "Bumper". Both are much better than "Upper Front", "Inside", "Lower Left" and "Underside" because when you hand off a file or return to it at a later date, the descriptive names will still make sense.
Parts work in a similar fashion to 'Material' tags offering an additional means of defining polygon groupings. Parts can be a useful way to define additional surfacing layers in the shader tree, especially in cases where the surface layer spans across two or more Material tags boundaries. They can also be useful when exporting geometry to other applications. Parts can be easily defined in the following manner.
In 'Polygons' mode, select the geometry you wish to assign the part tag to, in this case the lid of the teapot.
Select the menu bar command "Geometry > Polygon > Set Part..." to open the 'Polygon Set Part' dialog box. You can assign a new name or use the drop down context menu choose an existing part tag from the list. LMB-click the 'OK' button or press the 'Return' (Enter) key on the keyboard to assign the Part tag to the selection.
Once applied, part tags can be recalled in two ways. If you create a shader tree 'Material Group' item, within its properties panel, one can define the 'Polygon Tag Type' as a 'Part', and in the 'Polygon Tag' drop down menu, select the a part you defined in the previous step. When defined in this way, the affect of any shader tree items added to this group would be confined to the polygons grouped by the tag, masking the layers in the same manner as a material tag.
The second way to recall a 'Part' is to use the 'Statistics' viewport panel under the 'Lists' tab. Within the viewport, under the "Polygon > Part" section, users can recall part selections by using the +/- buttons in the left column of the panel. Here I clicked on the '+' symbol to activate the 'Teapot Lid' selection. Pressing the '-' button would deselect any polygons that contained that tag.
TIP: Users can add tags to curve elements in the same way that tags are added to polygons. Simply select the Curve itself while in 'Polygons' mode and apply the tags as demonstrated above. This can be useful when defining alternate/additional guides when styling a 'Fur' layer.
