How to use copy mirrored UV correctly

Video transcript:

Assalamualaikum. My name is Widhi Muttaqien from expose academy.

More often than not we need to create UV map for symmetrical models such as characters, vehicles, weapons etc. There are at least 4 methods that we can use to create UV maps for symmetrical objects. I cover all of these methods in my Udemy course “Blender 3D from zero to hero”. For this tutorial I want to discuss one of the methods, and that will be the “copy mirrored UV coordinate” command. For example lets create a monkey head object. Now for newly created 3D object we can add a default UV layout by turning on this “generate UVs” in here. So with this default UV layout, at least we have a starting UV layout to work with. We can see this default UV layout, if we go to edit mode and go to UV image editor, okay. Now, the problem with this layout is that it is not symmetrical. So when we need to create a texture on external graphic applications such as Photoshop or Krita or Gimp. We can not simply copy mirror the texture from right to left or vice versa. And of course, this condition will lead to additional time needed in the production process.

If we go to the UVs menu, we can see this command called “copy mirrored UV coordinate”. What this command do is actually comparing the 3D coordinate of the model and when Blender find similar mirrored coordinate, it will try to copy paste the UV data from one to the other vertex. So basically we can just create the UV layout for the right side only and have Blender transfer the layout to the left side. Or vice versa. But, for this command to work properly, we need to make sure that the original UV layout that we created only take half side of the texture space. Whether be the right side only or the left side only.

So lets do that now. In the 3D view, go to front view, press Z to go to wireframe mode. Unselect all of the faces and then press B and select only the right part. Our right side that is. Okay, because we only select the right part of the model in the 3D view, we get to see only the right part UV islands also in the UV image editor. Make sure we are in island selection mode down here. Move this eye UV island up here. And then move the ear UV island in here. Again, basically we want to have all of the UV islands at the right side not crossing this center line. Okay. Now for the head, we actually don’t want it to be separated from the left part. Essentially we want to make these vertices exactly at the center, so later it will adjoin with the left part UV island. To do that, try to move the head island to the center a bit. Then go to vertex mode now, unselect all, press B and select these vertices. Zoom in and make sure there are no unwanted vertices get selected. Okay. Now to make these vertices straight, we can press W to open the weld align window and then press A to auto align them. We can also use the S shortcut to go to scale mode, then X and then type zero and then enter. But that will require us to press more buttons than just W and A. Okay, now that we have these vertices straight. We want to move them to the center. If we don’t have any image loaded in the background, we have Blender’s generic texture size which is 256 pixels wide and 256 pixels high. So by knowing this generic texture size we can simply press N to open the UV image editor’s properties panel. And type in the X coordinate in here to 128. This should move the vertices to the center. Okay.

Now, what if we have an image open in the background and we really don’t care about the width of it. We just want to center vertices or UV islands to the center. If that is the case, you can turn on normalized option in here. What this normalized option do, is making the 2D coordinate system not based on image pixel size anymore but based on normalized values which is from 0 to 1. So this left line is now X zero and this right line is X one. The bottom line down here is Y zero and the top line up here is Y one. Because of this normalized coordinate values, we can center everything easily using 0.5 value.

Okay lets move on to mirroring the UV layout. Now go to the 3D view and select all of the faces. Go back to the UV image editor again, and make sure we have everything in here selected also. Go to UVs menu and then choose “copy mirrored UV coordinates”. Okay, now don’t do anything yet. We can see something awfully wrong here. First we’re mirroring the left to the right. It should be right to the left. Second, the eye UV island is broken in here. And third, we get error message that there are 2 duplicates found. If you miss the error message before, simply drag this info editor down, we can see the error message in the log up here. Okay so lets fix these problems one by one. In the 3D view tool shelf we can see the “copy mirrored UV coordinates” parameter, which is set to “positive” by default. Change this to “negative”. We can see now our UV layout looks much better. Now if you view you UV image editor in full screen, you can press F6. And this will open up the parameters we have in here.

Next is the problem with the broken eye UV island. This problem is actually what causing the error message in the log. So what is exactly causing the problem? This problem happens due to our monkey head 3D model has penetrating faces at the eye area. If we focus on the 3D view editor. Go to solid mode again. We can see these faces of the eyes, penetrating the base head mesh. This is what actually driving the copy mirrored UV command goes wrong. I don’t know if this is categorized as a bug or not. But this is what we have in Blender version 2.79a which I currently use when I record the video. So by knowing the problem, the workaround is very simple. We need to make the eye faces not penetrating the head. So select the eye faces. Move them to the front for now, so none of the faces are penetrating each other. Select all again. Go back to UV image editor. Make sure everything is selected just like before and then run the “copy mirrored UV coordinates” again. Now we can see, we have perfect symmetrical UV layout. We can see on the log up here that we don’t have any error message anymore. After we have the UV layout created we can go back to the 3D view editor. Select all of the faces belong to the eyes and then move them back. We can do this precisely by inputting Y coordinates. But for now, this should be suffice [seFAis] to explain the concept.

Okay guys. So that is how you create a perfect symmetrical UV layout using “copy mirrored UV” command in Blender. Again this is just one way to create UV map for symmetrical object. There are other 3 methods I cover in depth in my Udemy course “Blender 3D from zero to hero”. If you want to learn Blender from scratch, and master all of the in-depth 3D skills, in the shortest time possible. Then you should join this Udemy course. I have the link with discounted coupon code in the video description below. And as always, subscribe to my channel, share the video. Give a thumbs up if you like the video, and give a thumbs down if you hate the video. Check out my other tutorials. Wassalamualaikum.

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