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In animals and humans too, our skin is stretched over muscles that give our body shape. In R13, the new muscle system can give your characters any kind of shape you can imagine. What I have here is a very simple arm setup. I've got some joints and an arm mesh, so you can see that I have animated it, so that at frame 30 the arm curls up, and then it goes back down again by frame 60, so let's rewind it back to time 0. What I want to do is, I want to have this bicep deform as the arm curls up and that will be a much more natural state than just simply the rigid movement that it has right now.
So I need to use a muscle to do that, let's go to the Character menu and add in a Muscle object, and the Muscle object, when I first add it, is going to be huge, so what I want to do is I'm going to need to model this muscle into position on the arm. Before I can do that, I need to move these yellow balls called anchors, and these anchors need to be in position on the character where the muscle needs to start and stop. So let's switch to the Move tool, and I'm going to go to the side view, I'm going to grab each anchor and move them into position. I want the muscle to start about there and to stop about right there.
If I zoom in on that area, you can see it's a good position for the bicep. Now let's do that in a front view as well, and the bicep should actually start probably right about over there, and they're about right there as well, there we go. Now you can see our muscle is still way too big and we need to tweak it now. So I'm going to go into Point mode, and I'm going to scale the points of this object. Now adding muscles is a lot like modeling, you need to manipulate points and the Muscle objects have points. You can actually add more segments as well, we've got three rows of points and I think that's plenty for this type of shape, so we're going to start off by going into my Selection tool, making sure that Only Select Visible Elements is turned off, and I'll grab the top row of points, hit T on the keyboard, and I'm going to scale them way down, almost to a complete dot of points.
Now I'm going to do the same thing for the base, grab just those points and hit T on the keyboard and scale them way down into position. Then I'll grab the middle row points. Make sure that I don't have any additional point selected. Ooh! I can see I made a mistake, and that's why it's very important to orbit around your objects, so I'm going to undo until I find where I made my mistake. You can see there is where I made my mistake, when I was scaling those points down, I accidentally selected some points from the back side of my muscle. So let's hold on the Ctrl key, deselect those, and then now I know that I've only got that top ring of points, so I can hit T and scale them down, I can orbit around just to make sure that haven't messed up at all, and there we go.
Now I can grab those points, and I'm using the spacebar by the way to get back and forth between the Scale tool and the Selection tool. Now I can hit T again to get the Scale tool back up, and scale those guys down, and now I can grab just that middle row of points, there we ago, and hit T and scale those guys down into position. So what I'm looking for is the relaxed state of the muscle. What is the muscle shaped like when the arm is at its fully extended or fully open position? And I'm going to move these points over just a bit and back into position there, and just scale them down just a bit, and that's not too bad.
I'm going to grab the bottom row of points also and just scale them down a little tighter. Let's hide the arm skin a little bit, so we can see our muscle better. I'm going to hold down the Option key or Alt on the PC, and click twice on these dots to turn them both red. Now we can grab just those points at the top and scale them down, and now I can grab just these points, I think those are actually pretty good. Now this next step is very important. In the Muscle object, I'm going to go into the Object properties, and this Length field tells you what the relaxed state of the muscle is going to be.
Let's hit Set, and you'll see that it shifted dramatically down to 20 units from 200, that now reflects the existing length of our Muscle object, and that's very important. Now what we need to do is to link the muscle up to the joints that are going to help it deform, and so in order to do that we're going to take the joints from the Object Manager and bring them into these fields down here. So I'm going to start with the forearm and drag it down into this field, and when I do that, I now have my forearm there, let's get out of Point mode and back to Model mode, so we can see our anchor points a little bit better.
And now I can take the shoulder and drag it into this field, and you'll see that the axis shifted for that, now I've got a linkage here. Now this button right here is very important, Auto Align, I'm going to uncheck that button, and when I do that, now my muscle is not twisting at all, doing weird things, and if I leave Auto Align turned on, you'll see that as the joint moves, the muscle twists and does this weird thing, and I don't want it to do that. So I'm going to turn off Auto Align, and now what we need to do is find the compressed state. If I go to Compressed and inactivate that, I'm going to uncheck Auto Volume.
Auto Volume tries to automatically figure out what the muscle looks like when it changes shape, and we're going to uncheck that, because we want to define that manually. So when I do that, I now get this set field here, I'm going to scrub forward to the peak of the motion, and we're going to model this muscle into shape. So let's start off by going to Point mode, and then we're going to grab just the points in the middle of the muscle, and we're going to rotate them down in the position, they are a little bit twisted right now, and then we're going to grab the points that are at the base, you can see that ring there, that shouldn't be shaped like that either, that's because those things move as the joint moves.
So now I've rotated those points down. Now I can hit T on the keyboard and scale them down into position. Now I can grab the points in the middle of the muscle, and we're going to scale those up just a bit and then move them, we want that muscle to shift position and bulge outward like that, let's rotate it up just a bit, there we go, grab just the red handle and rotate those guys up just a bit, that's pretty good. Now we go back to the Muscle object, and we're going to set that Compressed length. Now when we switch over to Animate mode, you can see that as we move the muscle, it changes shape over the rotation of the joint, and that's the behavior that we want.
Let's turn on our mesh for the arm again, make it visible, hold down the Option key to do them both at the same time, let's scrub through the animation, you can see that the muscle pokes up out of the skin and that's very painful, we're going to fix that in a minute. More importantly though is that the muscle isn't yet deforming the skin, and so we need to fix that as well. So let's rewind back to 0, and I'm going to add into the scene something called an MSkin object, so I go to the Character menu and go to MSkin, and the MSkin tells the muscle what mesh to affect, and so we're going to take the MSkin and add it into the hierarchy here, and this is very important, you want to put it right below the Skin object, and it should go below the skin, so the skin gets deformed first, and then the MSkin moves the deformed skin, and because I had my muscle selected already, the MSkin in the muscle field already auto-populated this field here, but if I hadn't had my muscle selected, I would have to drag that Muscle object in.
Now, when I move my arm, I get a bulge in the bicep, and it pokes through and that looks extremely painful, so to fix that we're going to hide our Muscle object. They don't need to be visible, so I'm going to hold down the Option key and make both dots red, so that my muscle disappears, and now I can scrub that animation, that's really all there is to it. Placing the muscles is a lot like modeling, and you really have to study your anatomy well and then approximate those muscle positions to get the deformation you want. Notice I've got a weird looking bulge here, I can go back in and tweak those settings easily and that's really the beauty of the muscle process is that it's nondestructive.
The Muscle object is not just for characters, it can be used to deform lots of different objects, and it can be rendered with textures too. Experiment and have fun!
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