Trying to use the Vulkan viewport for transparency mapped hair cards is still unusable and unacceptable. The edges are not sharp but a pixelated mess even on high quality. There are still depth sorting and lighting issues. I don't know why SideFX has deemed this production ready, but it isn't for game dev.

Please tell me I'm missing some setting or something. I guess back to OpenGL again.

Edit: Well, OpenGL looks like it has all kinds of issues. Lights don't work at all. Wireframes don't show.

Vulkan viewport has to be the most disappointing update of Houdini. It's so bad. I really don't know how they have the audacity to make it the default option. Now Vulkan is pre-beta (at best) and OpenGL is getting depreciated. H21 is a DCC with a history of 30 years but with no production-ready viewport.

Until some form of order-independent transparency or alpha hashing is implemented, it looks like cutout is the only usable option in situations with overlapping transparent geometry. It seems like it uses any alpha value > 0 as 1, so adding a power after the alpha image in the material will allow you to control the alpha cutoff amount. I guess that will have to do for now, but hopefully this gets some attention in the future.

Cutout transparency works well because that case is the one cutout was designed to solve. There are 4 transparency modes in the viewport -- None (ignore alpha entirely), Cutout (pass/fail depending on alpha value), Low (topmost face only), and Medium & High (Order independent transparency, 4 or 8 layers). Because of amount layering involved with those cards, even Medium/High transparency doesn't produce great results (transparency is a bit of a problem for rasterizers). Also, when Work Lights are active, the viewport is limited to Low quality transparency to maximize performance. If you add a light to the scene, you'll be able to compare Cutout, Low, and Medium. IMO, cutout definitely produces the best result, though Medium/High is a bit better than Low.

It'd be useful to add a parameter to the Visualize Properties SOP to force Cutout transparency. We have something similar for Sprites but it's not generalized to all material rendering. A full ray tracing pipeline would also produce better results, but that's a ways off.