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Modonize: FAQs
General 3D
What is Sub Division, and what is Tab Doing?
Posted by
Leefmc
on
Sunday, December 17, 2006
(GST)
A question was asked on the Luxology forums on what exactly modo is doing when you hit tab. Compared to hitting D and manually Sub Dividing a mesh. This can be confusing to new users, and hopefully i can clarify it some. (In Theory)
Well the answer is that Tab is doing two things. It is Sub Dividing your mesh to a specified amount (Your "Sub Division Level") with the Catmull-Clark Algorithm (I believe), and it is turning Smoothing on. To better illustrate this, we can turn Smoothing off and see that there is roughly no difference between a group of physical, real polygons, and a Sub Divided group of polygons. (Also note that "technically" Smoothing is not turned on/off, it is just used differently when you hit tab on an object.)
Example: The below picture shows on the right, a cube, that has been manually divided two times (by hitting D), and on the left, a cube that simply has Sub Division turned on with a level of 2 and no Smoothing. You'll notice they are nearly identical.
Example 2: Here you can see i have selected some polygons on each object. You can see 4 selected on the right, which illustrates that those are real physical polygons. Where as the one selected on the left, you can see that it is only one real polygon, and the Sub Divided ones are just there because of the Temporary Sub Division Algorithm being applied to it.
Example 3: Here you can see the same two objects, with smoothing on. You'll notice they both change slightly. The one to the right, which is all real polygons, still shows all the faces. This is because all though it is being smoothed, those faces are all real and modo will not try and hide them from you. Where as the one to the left, modo is smoothing the object, and although the cube only shows 6 faces, modo is still rendering the same amount as the one to the right, they just happen to be none editable polygons.
(Note that although i do not know for sure, i believe modo does use slightly different algorithms to render these. So true faces (right) do render to the screen slower than subdivision faces (left).)
The two terms can be confusing, and although i confused myself, hopefully the illustrations explained it more than my words did. Another way to see this process is to take a cube, hit tab, then freeze the object. Make sure you fully understand that before you freeze the object, you only have 6 real faces; however, with a Sub Division level of two, after you freeze you end up with 96 real faces. The same as my cube above (right).
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