Subdivision modeling is little bit more advanced and universal technique of creating 3D models and that's why I've decided to cover it separately. There are many objects around us which have curved, organic and uneven shapes. Let's take vases from our sample picture - they consists almost only of very smooth, round surfaces with no straight, technical lines like the kitchen table from previous tutorial part. This is why we need a bit different approach to modeling and I'll try to describe its basic principles below.
Shading type defines the way Blender will display our 3D object both in 3D viewport and during the rendering. Flat Shading type was used by us in the previous chapter and works best with simple, not very detailed objects. Rounded edges are small enough so we don't actually see their angularity which is the main drawback of this shading mode. The other alternative is "smooth" shading, but it makes straight, technical geometry looks buggy.
There are two ways of solving this problem. First is adding an Edge Split| Modifier - what it does is splitting your model into different parts, (still within one object) depending on the face angles. This may work for non important, second plan details in your scene you probably need to build up quickly, however it shouldn't be used on bigger, more visible or important objects.
Second way is a bit slower but much more reliable and it's about adding new edge loops close to the existing geometry edges - this is what we actually call "Subdivision Modeling". The biggest advantage of this method is the fact that every model created this way will keep its actual shape, even if we add Subdivision Surface Modifier (which is not always working with Edge Crease technique and that's the reason I won't be covering it in my tutorial). Preparing your models this way also ensures that they will always work correctly, no matter in what 3D software you're going to use them (after exporting to obj format for example).
Subdivision Surface will be described more briefly in the next step, but I'd suggest spending just a few minutes on trying different geometry and shading types yourself. While in Edit Mode you can also assign different shading types to individually selected faces so your model has both Flat and Smooth Shading. However, keep in mind that changing the shading type later in Object Mode will overwrite all the changes you did.
After going through the previous chapter you may ask yourself - why not just use Bevel tool to round the edges and then turn the Smooth Shading on? The problem is that Bevel tool changes original positions of the starting and ending vertices of your selected edge. Even with Smooth Shading, applied, we still need to add additional edge loops that would fix the shading issues.
With all the basics described. let's now get deeper into learning "Subdivision Modeling" techniques. As I mentioned few paragraphs earlier, I still recommend trying and testing described techniques yourselves. You can use the most simple geometry types such as the ones I'm showing in my examples, or try creating some basic furniture models and see how they behave with different shading types and modifiers applied.
Let's continue with our table model we've started in the previous part. Center your 3D cursor over the sink opening and add a default cube. Scale it so it fits the hole and delete the upper face. In Object Mode, add Subdivision Modifier with at least 2 or 3 view subdivision levels.
With table model unhidden, I've adjusted shape of the sink so it fits the geometry better. It was also too deep so I had to change that. Now, without leaving the Edit Mode, select the upper edges and extrude them once outwards (just press S and scale outwards after extruding) and once downwards to create the rim. Add one more edge loop so the upper part of our sink doesn't intersect with the table.
This is our very basic, subdivision ready shape but we still need to tweak it. As you've probably noticed, what Subdivision Modifier actually does is generating new edge loops between our existing edges and loops we create in Edit Mode. If the surface is curved, the distance between vertices or edges defines how smooth or sharp the curvature will look like.
To explain it a bit better let's simply continue with our sink model. As you' can see, now it looks too even and technical which doesn't correspond to how real sinks look like. Let's start changing this by selecting our bottom faces and scaling them down in Y and X axes.
In the next few steps I will be still working on the sink geometry - this includes an overall shape as well as keeping the topology even enough so Subdivision Modifier generates nice looking mesh. At this point it would be also good to enable Smooth Shading as it gives us a better preview on rounded surfaces. You can follow my steps shown in the next picture but I would suggest using them more as a modeling reference and trying your own ways of creating the sink. You should already know some of the modeling techniques and it's a good opportunity to test them.
In this step we will be adding sink strainer opening in the bottom of our sink. One way of doing this could be using Boolean Modifier, however this usually generates messy meshes and should be avoided for precise modeling. The modifier is briefly described in the last part of my tutorial,. Now, let's focus how we can cut round, precise opening the easiest and most proper way.
As I mentioned earlier, what Subdivision Modifier actually does is generating new faces and edge loops between the ones already created in Edit mode while Subdivision Level defines the amount of newly created geometry. If we "apply" the modifier, all of the new faces and edge loops will be available for us to edit when we switch back to Edit Mode. Since our current model looks pretty simple, we definitely need to apply Subdivision Modifier with Subdivision Level set to 1.
After applying Subdivision Modifier, your object may have quite a lot of new edge loops generated. Some of these are necessary for a proper model look while others could be removed for better performance. This is especially important when creating models that will be distributed around the scene hundreds or thousand times for example: chairs in conference room. I would like to show you few quick ways for optimizing your 3D models and having a nice looking, clean meshes.
Cleaning up the mesh geometry may by a bit time consuming especially when you apply the Subdivision Modifier with high Subdivision Levels like 3 or above. What I recommend is always applying Subdivision Level 1, optimizing the geometry and then, if needed, adding and applying the modifier again.
Above you can see the result of spending few minutes in order to optimize and tweak the sink geometry a little bit. With this we also close this tutorial part.