Splinters
Making a surface mesh breakable clips it with the Tet Mesh. The fracture geometry is very angular and straight. This fine for crystalline materials but not for things made of other materials like wood or bricks. With DMM "splinters" are used to describe detailed fracture geometry. Splinter "cages" are optionally attached to DMM objects to assign splinters to the object after a surface mesh is attached, and this affects how the attached surface mesh is prepared for fracture.
A library of splinter cages is provided as a set of .obj files. Use the "Import..." menu item (under the "File" menu of Maya) to load a splinter cage from an .obj file or simply drag the .obj files into Maya (provided that the .obj export plugin is loaded). Once loaded a splinter cage is positioned and oriented and can be expanded or contracted in any dimension to encase the entire surface mesh for the DMM Object. The splinter cage can be duplicated if it needs to be larger without making it less dense. After placing the resulting copy beside the original too small splinter cage, it must be combined with the original because a DMM Object can have only one single polymesh as a splinter cage.
To associate a splinter mesh with the DMM Object after it is positioned properly,
select both the DMM Object and the splinter cage then select "DMM Asset >> Add Splinters to DMM Object"
menu item. Alternatively, click on the appropriate shelf icon.
Splinter cages can also be made from a 2D texture map (currently only .bmp format supported).
The splinter cage is an extrusion of the pattern found in the texture map.
A single layer splinter cage made from a 2D texture map is good for brick walls and glass.
For materials that tend to have more depth, like wood, several 2D texture maps can be used
to produce multiple layers.
The layers are combined into a single mesh, then the result can be attached to a DMM Object
as a splinter cage.
Choose "DMM Asset >> Create Splinters from Image..." menu item and pick an appropriate bitmap.
A Splinter Cage will be added as a polymesh to the scene.
The appropriate icon of the DMM shelf can also be used.
Splinters are seen in the output simulated surface mesh when fracture occurs and only in the area of fracture. Setting the DMM Object node "Start Splintered" attribute as true will show splinters even before fracture occurs.
It's important to realize that, once there are fractures, each involved splinter cell is controlled
by one tetrahedron (which is the one with its centroid the closest to the splinter cell centroid).
If the splinter cells are much bigger than the tetrahedra, then only a few tetrahedra will end up
controlling the splinters cells. This can lead to a visual result that differs quite a lot from
the simulation.
In the example below, the splinters are drawn in blue and the tetrahedra are drawn with
a semi-transparent red shader, and for better visual differenciation the edges are green.
The two results are quite different because the splinter cells are much bigger than the
tetrahedra. It is recommended to keep the volume of each splinter cell equal to or smaller
than the volume of a few combined tetrahedra. A good rule of thumb is to have about three
splinter cells per tetrahedron.
Requirements for Splinter Cages
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