From the course: ZBrush: Tips & Tricks

Decimating flat surfaces - ZBrush Tutorial

From the course: ZBrush: Tips & Tricks

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Decimating flat surfaces

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- Here's another work around for a common ZBrush glitch. When decimating objects that have flat surfaces next to open edges you can sometimes get unpredictable results. I'll show you how to keep that from happening. Okay, so we've got this mountain range and let's say that we need to decimate it. It's about one million points and let's say we need to take this to some other program and it's just too many polygons we need to decimate it. So the normal way to do this is to go to zplugin, decimation master, set the percentage of decimation. I usually like to bring this down lower maybe like around five, and then let's pre-process it, and it's just going to take a moment here to calculate which polygons have more detail and which ones have less details. If there's a large flat area that area gets prioritized for decimation, whereas if there's lots of detail then those areas see less decimation. Okay, now that it is done processing go back to zplugin and we'll go to decimate current. If we hit Shift + F to turn on wireframe you can see that it kept a lot of polygons in the high detail areas, but it got rid of polygons in the low detail areas. You could see that one unfortunate side effect from this is that Zbrush didn't really take into account that we might want to keep the corners on those open edges. So it just kind of literally cut corners to decimate this. So let's hit Control + Z to undo that. Shift + F to turn off wireframe. First I'm going to look at one method that will freeze and lock the boarder edges so that they won't get decimated. So let's go to masking and we want to mask my features. I want to mask the boarder edges, so we can just turn off groups and crease and just click on mask my features with boarder active. We zoom in really close here, it might be hard to see, because this is really high resolution mesh, but that very edge is now masked off. All right, so let's run that decimation one more time. Let's pre-process current. All right, now that's pre-processed let's go ahead and run that decimation. Okay, let's hit Shift + F to see what happened. So basically the same thing here in the high detail areas, but on the boarder edges it kept every single polygon. Now this kind of creates a really weird, it might not necessarily be a problem, but it's kind of weird where all of these edges are retained from the original model so it creates this kind of strange pattern of really long thin polygons, which may or may not be a problem. So if this is an issue and you don't want to go forward with this let me show you a second way to do this. Click Control + Z to undo that, Shift + F to turn off wireframe. The second step involves turning this object from a flat surface into a curved surface so that the decimation will read all of the surfaces as at least a little bit curved and therefore it won't want to cut the corners off of flat surfaces. So the one interesting way to do this is to go into deformation and there's two deformers in particular that work really well with this, one is twist and the other is gravity. Let's try twist, so what I'm going to do ... Oops I still have the mask on the boarder. Let me hit Control + Z to undo that and I'll just clear the mask, going into masking and clear and back into deformation. We can go with the twist. Lets drag it all the way to the left. So you can see what this is doing is it's twisting the shape basically and turning those flat surfaces into curved surfaces. So if you run the decimation on this and then you go back to twist and you run it the opposite direction it'll untwist and come out exactly the way it was before. Gravity, kind of a similar thing here. Let's drag it all the way this way and it just kind of creates a bowl shape out of everything. Then if you run the decimation and then take the gravity and run the opposite direction it'll go back where it was before. So let's actually test this out. So we've got the gravity and we just hit Control + Z to undo this just to make sure I'm doing it exactly right, okay. Let's drag this all the way to negative 100, go to zplugin, pre-process current again. Now that it's processed we'll go and decimate it. Let's hit Shift + F to see that wireframe. Okay, so you can see it's not being nearly as aggressive when it comes to decimating these polygons. So we can go to gravity now drag it back in the opposite direction, turn off wireframe, and you can see we've not got our decimated mesh without any cut off corners. Now this geometry is ready to render in Maya or send to some other program.

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