User:Chris Blackbourn/BlogDraft

This blog post will spotlight Chris Blackbourn's work on UV editing tools since mid-2022 and the latest enhancements available now in Blender 3.6. Furthermore, he'll give us a preview of potential updates to anticipate in Blender 4.0.

A New Approach to UV Packing

In Blender 3.6, the UV packing is considerably faster and smarter. The layouts use less space and are packed more tightly. Let's explore this new feature.

The Turbocharged Alpaca

At the heart of the strategy is the new "Alpaca_turbo" packer. It's designed for speed, capable of packing millions of islands in just a few seconds.

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Here we can see the Alpaca in progress. The islands are already sorted from largest to smallest, and the light green rectangle on the bottom left shows islands which are already placed and cannot be moved. Islands are placed sideways across the top of the existing rectangle until we get to the edge. Next, we start on the bottom right side, and keep placing islands until we get to the top.

Then repeat.

Of course, that's where the name comes from, the Alpaca is really the "L"-Packer, named after the "L" shaped pattern it uses to place the islands.

One huge advantage of the Alpaca is the way it combines with other packers. In Blender, the largest 1000 islands are packed with a conventional packer into the rectangle in the lower left, and then the Alpaca_turbo takes care of all of the rest of the islands.

In this way, by combining other packers with the Alpaca, regardless of how many islands you're packing, you always get a great result in a reasonable amount of time.

The Xatlas Approach

The "xatlas" strategy forms another key part of our approach. It leverages bitmap occupancy to achieve an incredibly tight pack. With added tricks to handle both exact shape (concave) and the convex hulls, xatlas provides high-quality layouts without compromising on speed. (Blender's implementation of the xatlas strategy is inspired by the original reference implementation over at xatlas.)

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  PNG Version

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  SVG Version

Here we see an example of the "xatlas" UV packing algorithm as implemented in Blender 3.6.

Packing, Optimally

Single islands are now packed optimally. The island touches all four sides of the unit square.

Many layouts consisting of quads are now packed optimally, including this surprising example with 18 equal sized squares.

For the first time, Blender now includes optimal packs. For a few important types of islands, we can now produce layouts which are "optimal". While the optimal layout is not unique, we can show mathematically that there is no tighter pack possible.

More Packing Features

We've added lots of new options too, for pinned islands, rotation options, pack to original bounding box and merge overlapping.

Check out the official packing documentation for all of the details.

Putting it together

With these improvements to Blender's UV packing, you can now expect to see a major reduction in wasted texture space, and thanks to the speed of the Alpaca_turbo packer, you can pack even very complex models in a reasonable amount of time.

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What else is new in UV Mapping in Blender?

Good UV Mapping starts with a balancing act. We always have to trade off distortion against seams against texel density.

Lets dive right in by repairing this seam with Unwrap Selection

Close up of UV Editor with default monkey object.

After UV Unwrap Selected

After minimize stretch

Great! Now we can reduce the distortion with Minimize Stretch. BTW, it now fixes flipped faces.

After geometry relax brush with pins

Okay, time for texel density. Lets pin those corners and switch over to the new geometry relax brush which uses the shape of the geometry to drive the shape of the UVs:

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Average Islands Scale

Average Islands Scale (original)

Average Islands Scale, Non uniform and Shear

Lets explore two new options in Average Islands Scale to improve the quality of your unwraps.

The original version evens out texel density between different islands.

• With the new Non-Uniform option, differences between the U axis and V axis are balanced.
• With the Shear option, the U axis and V axis will be balanced back to 90°, even further reducing texture distortion.

Copy and Paste for UVs

One great new feature in Blender 3.6 is the ability to "Copy" and "Paste" UVs. This works great for gaming workflows where you might have repeated geometry for eyes, hands, or even larger pieces like arms and legs. For hard surface modelling, it works great on rivets, switches, bevels, spokes, chains etc.

Just select the UVs you want to copy, copy them, and then paste them onto the UVs. This works between UV layers, and you can even copy UVs between different .blend files, as long as the topology matches between the geometry of the source UVs and the topology of your target.

Blender 4.0

... TODO ...

• More game developer features.
• Better UDIM support.
• Automatic seam placement.
• Maybe it’s a One-Click “Just Unwrap It For Me” button.