Discovering Blender Sculpt: The Third Installment

The real benefits of blender sculpt mode is achieved when a model is using multires(multiple resolution) mesh. There are a few things though that we have to take into consideration before we begin using multires.

The Base model.

This is the core, the model before multires has been applied and I have noticed that there are some do’s and don’ts when it comes to creating the base model.

Don’t over complicated it, speaking from my own experience I find that because I’m used to sub-surf modeling I will try to add detail when I don’t have to. Leave the detail to the multires levels. A simple base model can be more flexible to work with than a complicated one.

Complex topolagy vs Simple

Avoid Triangular faces/polygons(tri’s) if possible or at least hide them somewhere they wont be noticed.

Think like a game modeler, simplicity is the key and no one strives for simplicity like a game modeler. Look on the internet for low polygon modeling to give you an idea.

Face/polygon’s should be as square shaped as possible, avoid rectangular shapes these can cause  unwanted lines in the displacement.

Rectangular face vs Quad

I hold the view that mulitres biggest benefit is in the creation of displacement and normal maps, therefore the base model itself does not have to be animation ready. What I mean by animation ready is that I don’t need to take special consideration on how and where parts of the mesh will bend(for rigging).

Getting the most by crashing Blender

(The following is a bit sketchy but I feel that its still worth the mention.)

I found that the best way to get the most from multires modeling is by crashing blender. Be warned though I will not be held responsible if you loose data or your computer goes BOOM, BAAM or starts making a funny beeping noise (although the chances of something like that happoneening is next to nil). You should be aware that you will most likely have to restart your computer afterwards, to free up your RAM. At first it may sound a little odd that I would want to crash blender(or even my own computer) but there is logic in my thinking as I will explain… When I add a multires level to an object, it will divide up a single square face up into a multiple of four. Simply put 1 face/polygon becomes 4 faces/polygons.

1to4

This fact is clearly obvious when brought to light but I found that I only started to take it into consideration after trying to improve performance in multires. Let us begin by looking at a single face we can see how the number escalates after adding on one level after another.

level 1-> 1
level 2-> 4
level 3-> 16
level 4-> 64
level 5-> 256
level 6-> 1024
level 7-> 4096

OK now consider this… I have a base model at level 1 with a face count of 2000, which means at level 7 that face count will be 8192000. The math is simple but clearly demonstrates the problem because while the face count goes up and up in multiple of 4, so can the strain on my computer(RAM, CPU and graphics card). This is where crashing blender comes into play. I need to know at which multires level blender will get too before it crashes or becomes unstable and unusable. Lets use the previous example of level 7 with a face count of 8192000, I mananged to get to level 7 but I find it to be very sluggish, to the point of unusable. Clearly there’s no point in adding another level. However at level 6(2048000 faces) blender was running smoothly, now consider the difference in face count between the two levels, isn’t it a waste? I could still get more out of it. The guessing game starts here, I ask myself at what face count the multires could increase too yet still allowing me to model/sculpt without any serious lag, 4000000, 5000000? Ideally I would want my model at face count of 5000000, so I take that number and start to divide it by 4.

5000000
1250000
312500
78125
19531
4882
1220

19531 faces is too high for a character base mesh, I would be looking for a face count of either 4882 or 1220 and when I create the base mesh I will try to get the polygon count as close to that number as possible. This though is the perfect theory for the perfect model, like a cube or a mesh completely comprised solely of square faces(quads). Its extremely difficult in character modeling to have a model composed entirely of quads without a single tri.  When tri’s are added to a model, dividing 5000000 by the value of 4, is thrown out the window. Not to worry though, I thought it best to start with the simplest example and work form there. The following is how I would approach the problem of base mesh estimation. First I need a base model to practice on. When modeling the base model I take advantage of useful features like the mirror modifier which will cut work load in half. Once I’m happy with base model model (make sure that its the only object  in the scene) I take note(write it down) of the face value which can be fond along the top most bar.

facecount

Then I add a subsurf modifier to the model. Reason why I do this is that the subsurf modifier will divide up a faces in a similar way as multires.In object mode take note of the face count value. So now we have two values, my base model 468 and the subsurf level 1 value 1864, now for the simple math first we divide the the subsurf value by the base value.

1864 / 468 = 3.982905983 (important do not round off!)

Then take the 5000000 estimate value and divide it by 3.982905983 to the power of 7(its quicker than continually dividing the result by 3.982…)

5000000 / 3.982095983 ^ 7 = 314.46

314 should be the ideal face count for the base model, I now need to get as close to that number as possible. Obviously though if I had a simple base model to begin with, I might not be able to get close to that value by removing faces/polygons.  I have no choice but to go up to the next value(5000000 / 3.982095983 ^ 6 = 1252). Apply the subsurf modifier at level 1 to the model. With that I have more faces to work with and I managed to get my face from 1864 count down to 1244 without to much bother. When removing faces from the model I look for face loops in areas like the arms, legs and waist and remove them from areas where the wont be missed(functions like collapse and edge slide help). Avoid removing tri’s. To see if it has worked I will use the subsurf modifier again and then start increasing the levels until it gets to around the 5000000. If I’m happy with base model I’ll deactivate the subsurf modifier then apply the mirror modifier to the mesh to make it whole. Now all that I have to do is start using Multires.

The Multires Panel rundown

Multires Panel

Add multires: This button is self explanatory. I will mention this however that if you have you where using the subsurf modifier before applying multires, make sure its removed.

Add level: Adds a level which will contain more faces than the previous allowing greater detail to be added

Del Lower: I you are on level 2 for example and level 1 has become useless or you don’t need it any more press Del lower.

Del Higher: If you are on level 6 for example but you made a mistake on level 7 or maybe level 7 put to much of a strain on your system press Del higher. Edges: you may have in the past played about with this button but noticed that it wasn’t doing anything. To actually understand what this does we have to first go to the object settings(F7) and select the “Wire” button. Magically a wire frame has appeared on the solid model. Go back to the multres panel, now let say that I am already on multires level 5, edge 1 views the wire frame of level one. If I wanted to view the wire frame of level 3 I would set “Edge” to 3. It is very handy visualisation tool and will eventually  become indispensable the more you use it.

Edges

Pin: … haven’t really used this option yet but supposedly has something to do with how much of an effect a modifier will have on the multires model.

Render: determines the multires level to be rendered, comes in handy when render baking.

Modeling with multires

I honestly feel that this can not be taught by reading a tutorial. Saying that though after viewing many websites and tutorials on mudbox and zbrush there seems to be one bit of advise that pops up again and again… Focus on one level at a time and do as much as can be done in that level then proceed to the next. Other than that its just getting used to the tools and gaining experience.

<-Discovering Blender Sculpt: The Second Installment

Discovering Blender Sculpt: The Final Installment->

Content Copyright© 2009 Lindsay C. Kerr

Advertisements

About this entry