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Material Group

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Material Groups can be thought of as containers that hold any of the various shader tree items, such as Shaders, Materials, Textures, and even Render Outputs. These containers can be useful for simply organizing the shader tree, but are incredibly powerful when used to control how surfaces are applied to polygons at render time. Referred to in in the Shader Tree 'Add Layer' function as a 'Group', here they are referred to as a 'Material Group' to avoid confusion with 'Groups'.
Surfacing in MODO is separated from the geometry. Individually, Shader Tree item layers affect an entire scene, until limited to specific areas by way of a mask. The masks themselves are procedurally created, and defined by 'Polygon Tags'. Tags are simply bits of information tied to a polygon that associate it with a particular grouping. The most common tag is a 'Material' tag that, when applied to any polygon selection using the 'M' key shortcut (or 'Texture > Assign Material Group...' in the menu bar) automatically creates an appropriately named 'Material Group' layer in the shader tree with the proper tag specification and a 'Material' sub item. Once created, changes made to the various layers under the 'Material Group' will only affect the polygons with that tag. Since polygons can only have one type of material tag at a time, additional layers masks can be applied using 'Selection Sets', polygon 'Parts' and item masks.
These masks that the Material Groups define are based on the settings under the 'Group' header. They can be used individually, or in combination, and while the functions may appear simple, they are an efficient means of surfacing a scene. Understanding what each does is an important step in understanding the shader tree itself, and realizing the power that the shader tree provides.

Group Item PanelLayer--

Enable: Toggles the effect of the group (and its contained layers) on and off, duplicating the functionality of toggling visibility in the Shader Tree. When un-checked (disabled), the layer has no effect on the shading of the scene. However, disabled groups are saved with the scene and are persistent across MODO sessions.

Invert: Inverts the RGB values for the group producing a negative effect.

Blend Mode: Affects blending between different groups, allowing user the ability to stack several groups for different effects. For more on blending, please reference the 'Blend Modes' page of the documentation.

Opacity: Changes the transparency of the current group. Reducing this values will increasingly reveal lower layers in the shader tree if present, or dim the effect of the layer itself on the surface.


Item: The 'Item' selector can be used to limit the application of the layers contained within a material group to a specific mesh item (these are the mesh item layers of the Item List). When defined, these are considered an 'Item Mask'. The '(all)' setting applies the materials to the entire scene. This setting can also be used in combination with a polygon tag, further limiting the surface.

Polygon Tag Type: Users can specify the type of polygon tag; several types are possible. Each limits or masks the application of the shading items contained within the group to only the polygons tagged as such.
Material-- The most common polygon tag type, Material Groups with this type of tag and automatically created when using the 'M' keyboard shortcut. Polygons can only have one Material Tag at a time.
Part-- Parts tags are similar to a selection set, but like a material tag, a polygon can only belong to one 'Part' group at a time.
Selection Set-- Selection Sets can be useful for recalling previous polygon selections, however, when specified here as a tag type, the selection set will mask the material groups layers to the associated polygons of the specified selection set. One polygon can belong to many different selection sets.

Polygon Tag: When any type of tag is created, be it a 'Material', a 'Part' or a Selection Set, the user is presented with a dialog box requesting a name. All tags of the defined type contained in the scene will appear here, where users can use this drop down to select the particular named tag they wish to use.

Scope: The affect of the material groups layers can be further limited to only 'Fur' materials, just the polygonal 'Surface' or to both with 'All'. As a fur material typically derives its surfacing from the underlying polygons (technically from the surfaces material item layer), duplicating a material group and setting the scope to 'Fur' will allow the user to specify surfacing attributes exclusive to the fur layer(s). This is how it is possible to have green grass growing from a brown dirt surface.

Layered Fur: Enabling this checkbox will allow multiple 'Fur' item layers with different settings on a single surface.

Apply to Sub-Group: Using undefined 'Material Groups' (Groups where no tags are specified) can be a convenient way to organize shader tree layers. With the addition of the 'Apply to Sub Group' option, they can also be an effective way to apply a setting to a number of material groups all at once. In the example below, there are 3 colored spheres, a box, and a ground plane. In the shader tree, one can see that the 3 colored spheres are grouped together into an undefined 'Material Group'. Directly below the group parent, a checkerboard texture has been added (next to the red arrow). Since it is above all the other layers in the tree and the group above it is undefined, it affects the entire scene; as illustrated by example one. By simply enabling the 'Apply to Sub Groups' option to the top 'Material Group' layer, the checkerboard effect is limited to those material groups that are descendants of the group as illustrated by example two. By setting the checkerboard pattern to 'Normal Multiply' as the blending mode in example three, one can quickly see how powerful the 'Apply to Sub Group option can be for quickly and easily applying a single texture layer to multiple surfaces.

Apply to SubGroups

Tip icon

TIP: As item layers and materials add up in the shader tree, it can quickly become a long list that gets confusing and tedious to edit. While there are many functions that speed and simplify the task of locating certain layers (such as the material selection mode), good Shader Tree organization is important. Users can select (highlight) multiple related layers and press the keyboard shortcut 'Ctrl+G' which will automatically group together the selected items. In this case the Material Group creates no mask for shading, but is simply used as an organizational tool. Renaming the layer will further help in identifying it in later sessions.



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