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Edge flow can be a challenging thing to get right. There's the theory behind it that I mentioned in the last movie, but there's also a lot of practice and experimentation that goes into a thorough understanding of it. Hopefully, with the following tips you will gain a better understanding of what goes into good edge flow. Let's open up the head_linesdrawn exercise file to look at what a finished edge flow drawing looks like. It's a Ztool, so I have to click and drag to bring into the canvas. Let's go into Edit mode and I'm going to hide the Light Box. I'm going to hit F, so we can see it full screen.
Okay, so I use different colors than you saw on the last video, but it's the same thing really. The first thing I want to talk about is keeping it clean. This means to avoid the temptation to follow every little detail, and instead focus on just the things that have a structural significance. So you see all the major structures of the face have been followed with edge flow lines. However, I want to zoom in here on one thing and note how I didn't follow every little detail. So you see there's this little line here on the bridge of the nose area? Little things like that can sometimes distracts from the big picture.
You don't need to follow every little detail; it's just the bigger forms. It's about following the structures that are actually going to move and change when they're animated. Something else to keep in mind is keeping it roughly even and proportional. Keeping every single polygon a perfect square is impossible, but you should try to avoid making any polygons that are more than twice as long on one side than they are in another. So you see most of these polygons are roughly square. Some of them are longer, a little shorter, but mostly square.
Now there is one big exception to this. You want to make edges closer together at creases and tight areas. So you look here in the laugh line. We've got edges that are closer together. Same thing around these creases around the eye. They are really helping to hold that crease shape. It's okay to have long polygons in these instances, because you want the model to be able to retain these long finer lines. You also want to avoid making abrupt changes in scale with small polygons next to really big ones.
It's okay to have small polygons in areas of tight detail, like around here in the corner of the eye or in the nostrils, and then you want to have bigger ones in big broad areas where not so much is happening. The important thing is to make a gradual transition from one to the other. Something else you want to do is avoid poles. Poles are when you have six or more edges meeting in one spot. It's like the grid lines on a globe meeting at the North Pole. Poles are difficult to sculpt and rig properly.
So I don't think I have any poles in this model. It's pretty free of that problem. But I do want to point out that there are places where you're going to have five edges meeting in one spot. So, for example, right here. Down here on the jaw line you've got another one, and back here behind the jaw there is another area where five edges meet in one spot. It's impossible to entirely avoid those five-pointed stars as they're called, but what you really don't want to do is have six or more edges meeting in one spot. That can cause weird pinches to form as you're sculpting, and it makes it difficult to rig.
Notice all of these polygons are four-sided. A few triangles are actually okay, but use rectangles when feasible. When a model is subdivided, triangles actually turn into rectangles. So one thing you can do is intentionally retopologize with triangles and then when it subdivides all those triangles will turn into four-sided polygons. Another good thing to do is retopologize at a lower density than you know you're going to need and then export at a higher subdivision level for animating.
It's also a lot less work to retopologize fewer polygons than it is to retopologize when you have drawn out a lot more lines. Now this edge flow drawing is not perfect. There are some things I would want to change. So, for example, there is this one edge right here that's going a little closer to this edge next to it than the other one. Something I would want to do is fix this by redrawing this line so it's a little more centered. Something else I would want to fix is to look out for faces like this. This is actually going to end up being a five-sided polygon, and we don't want that.
So you would want to find a way to split this maybe into two four-sided polygons or maybe a triangle and a four-sided polygon. Maybe you could draw an edge from this point and take it up into the nostril, something like that. Experiment with it. See what works. Something else I probably would want to do before I go into retopology is to spread out these edges right here across the nose. They are all kind of bunching up in one spot. I'd probably try to bring this one up higher, just kind of scoot all these up, and some of these down, just so that they're not all bunched up right here.
Keeping these tips in mind will help not just with retopologizing models in ZBrush, but with any kind of 3D modeling. It's a lot to remember, I know, but the more you practice it, the more you'll internalize these rules, and beautiful topology will come naturally to you.
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