How to mirror a UV map using only vector nodes?

Question

I want to create a material node setup that mirrors a UV map on X and Y axes. If I don't need to prepare a mirrored version of the image (4x the pixels) it will save time and memory.

I have managed to do this using a sort of complicated setup with lots of math nodes and a color ramp, but I think there must be a simpler and memory-efficient way.

Here I have the 4 corners mapped out individually, and can preview each one at a time, but I don't know how to combine them using only vector math.

Desired result:

Thanks in advance to anyone with vector expertise who can help.

Answer 1

This starts off by taking a slightly different approach than Đặng Hải Phụng and make the coordinate space of your plane stretch over -1 to 1. By default this will just tile the UV.

Then we use a Vector Math -> Absolute node so that negative numbers are treated as positive. This gives us a mirror effect on each axis.

Answer 2

Because blender allows colors and Vectors to be interchangeable in some cases (Both are Vec3 Containers), you should be able to get away with mixing your vectors using MixRGB Nodes blocked off with masks (exemplified in my image by the Separate XYZ and Greater Than Math nodes on the X and Y axis). Using a combination of mapping nodes to orient the initial images (especially scale by -1 on an axis to "flip it") and the masks, I was able to make this. It does use some Object texture coordinates, which I hope isn't a problem for you. I'm sure it works with UV too, I just have to find time to test it. I'll re-upload the modified .blend to save you the time of rebuilding it.

Let me know if it helps, or if it needs some alterations.

File is here -

EDIT - It works fine with UV coordinates (instead of object for the separate XYZ) - just change the Greater Than thresholds to 0.5

Answer 3

Note: Sorry I didn't read your questions carefully. You already worked out this solution, but I'll leave it here for others to have a look.

here's another approach:

First start with what the texture space should look like? With the understanding that Blender maps the texture (0-1) onto the texture coordinates (0-1), and the texture coordinates being 0-2 due to the tiling value set as 2, so we need to somehow make the texture coordinates become x (0 -> 1 -> 0), y (0 -> 1 -> 0).

This means the part 1->2 become 1->0. We can achieve this by using the mapping node, which allows us to map from one range to another. This node operates in the 0-1 space, so we need to divide the original coordinates by 2, perform the mapping, then multiply them back.

The mapping that needs to be done is (0.5-1) --> (0.5-0), so this means we map 0.5 to 0.5, 1 to 0. The (0-0.5) need to remain the same.

The node setup looks like this:

Answer 4

I have since found one more way to do this that is really simple. You essentially just need to remember one node... Math: Ping-Pong

With the Scale value left at 0.5, drop one of these on each axis. (The Z axis won't matter for flat image textures, but it does enable the mirroring of procedural volume textures.)

After recombining the axes, a Mapping node can be used for adjusting the Location and Scale of the UV.

Here's the setup inside a Group node: