Simple but effective trick in ZBrush to bridge 2 curves to create organic geometry
This is going to be a quick guide to show you a simple, but really cool trick to create certain types of cloth and drapery in ZBrush. The idea for this tutorial came from a work-in-progress from the second part of the double action brushes tutorial:
I used this simple object to show the effect of a custom brush I made to sculpt folds and drapery. Some of the questions I got, were about the test object itself rather than the brush. So, I thought I should show you how you can go about creating cloth without leaving ZBrush.
Although the technique in this tutorial might not be the most efficient way to approach a complex dress design or a tunic for your characters, it certainly is a fast way to test and produce intricate shapes as a starting point. You can refine it further and combine this technique with other ZBrush process to make a more interesting piece of cloth:
We need to have two objects living in the same subtool. The objects can be anything, a couple of planes would do the job, but I’ll use spheres to show you that it can be done on any object (I know that the object of this example is boring, but it’ll get better).
It doesn’t matter where you place the objects as long as there is (ideally) some distance between them. I just duplicated my sphere and moved it up.
Also make sure you don’t have any masks or subdivision levels in your objects. If you do, clear the masks and delete the subdivision levels before the next step.
Here is where the bridge curve brush works really well. We are going to use it to create the cloth by bridging the two objects.
Select the bridge curve brush (shortcut: “BCV”) and draw a closed curve in one object. The idea here is to create the two ends of a piece of cloth, where each curve is the “border” or the “edge of that cloth. Make sure that the curve you draw, faces the other object:
You can start from the bottom or the top. For this example I created the curve for the top first, because the bottom was going to be more complex than the one at the top.
Now that you have your first curve in one object, you can draw the second curve in the second object. As soon as you release the “click” after creating the second curve, ZBrush will bridge the two curves together with geometry.
As you can see, this is a very simple process, but for the first few tries, you might get things that look a bit weird. So, here are the reasons why your piece of cloth might look weird and how to easily fix it.
If the bridge section looks like the image below, its probably because we are creating a tubular shape (in this case) and the resulting mesh has the normals facing inwards.
FIX: simply click on the “Flip” button under the display properties in the tool palette. This will invert the normal’s direction including the spheres, but since they are only objects to help us build the cloth, we can leave them “flipped”. Alternatively if you need the normals facing inwards, you can turn the “Double” switch ON (orange) to see the mesh better.
If there is a missing section or a hole in the bridge, it’s because one or the two curves are not closed properly.
FIX: Zoom in to the beginning and/or the end point of your curves, to find the one that has a gap. Click the end point and move it towards the beginning and ZBrush will automatically close the gap. Alternatively, if the distance between points is too much, you can draw an extra section of the curve to close it.
This case is rare, but I remember it was an issue in older versions of ZBrush. If the bridge section looks weird like it is twisted, it might be because you drew the two curves in separate directions. This is more likely to happen if the curves are very swirly and complex.
FIX: Fortunately you can undo and redraw the last curve so if you get this “twisted” result, just draw the new curve in the opposite direction.
Now, we need to separate and clean up the mesh we just created. You’ll notices that when you draw the second curve to create the bridge, ZBrush automatically masks out the two objects. This is awesome because all you need to do, is split the masked points (or unmasked points – same result). From the subtool palette, under “Split” click on the “Split Masked Points” button. This will give us the “construction objects” (spheres) in one subtool and our piece of cloth in another subtool.
We could leave it here and just start sculpting details with the drapery brush for instance, but in some cases it would be better to have thickness. So the first thing we are going to do, is use the ZRemesher to create a cleaner topology.
The amount of polygons for the ZRemesher process is up to you, but I’d recommend to go for a very low number so the resulting mesh is easier to manipulate. Remember we are just creating the base for our cloth, you can go crazy with details and folds later.
With the Zmodeller brush (BZM) selected, hover over a single face and press space bar. Make sure you have the “Qmesh” selected as the action and “All polygons” as the target. Click on any face and drag to create the thickness.
Keep in mind that if you have a lot of polygons this process will be very slow, this is another reason why I suggest you keep a the poly count very low when Zremeshing.
Ok, so those are the basics. I know the object we just created doesn’t look very exciting and you are probably thinking… “i could have done that with a cylinder”, and you are right. However, now that you know the workflow and the tools, you can go ahead and take this to the next level. As I mentioned early, once you have your base mesh, you can use other ZBrush processes for more complex stuff.
For example, let’s replace the spheres we used as our “construction objects”, with two planes.
Now, mask an irregular shape on each plane (I subdivided the planes a couple of times and deleted the lower subdivision levels, to get a sharper edge in the mask).
To “cut out” the mask from the planes, we’ll use the extract function (Tool > Subtool > Extract) without thickness (set to 0). Also don’t forget to click on Accept to complete this action:
Now, to create the curves manually along the edge of these object would be very time consuming, fortunately we can use Frame mesh (under stroke > Curve functions) to create curves following the edge of the objects.
With the CurveBridge brush selected, click on a curve to close them. This looks more interesting, maybe a skirt or a table cloth? Now simply follow the steps we discussed earlier on, to split and clean up the mesh and give it some thickness.
Now that we have a decent base mesh with clean topology, you can begin to add folds and move things around.