I hasitate of taking part in this thread, mostly for a reason aRtye pointed out (and such shitstorm happens to happen from time to time here), but just for a sake of clarification and to answer original poster which seems to have a point and keeps polite tone, I'd like to say few words if you don't mind.
If some of you is unhappy with Houdini's builtin renderer, you should do exactly the same thing you do in case of Softimage/Maya/Max/Modo/Lightwave/Cinema4d - buy a proper renderer for your needs. This should serve you better than rants. I'm not saying you should stop making constructive critique, just keep it in the right perspective, which seems to be a problem - at least from my perspective.
Why on earth you expect Houdini builtin renderer will fight against entire universe of standalone solutions from whom every single one is developed by a team of programmers probably equal to SESI's core team? Go ahead and test Mantra against renderers provided to you for free with your favorite package. This would be fair starting point to discuss through and additionally would help you to realize why Mantra is awesome enough to be used successfully by many for two and a half decades (15 years in my case).
Mantra is developed from particular perspective of VFX industry, and while techniques developed by some major renderers in other contexts seems to payoff in VFX recently, they still provide a questionable value for many of our day work. I understand this is not somethings freelance audience cares about, but just keep in mind, that techniques which make VRay particularly good for static interior scenes are most of the time no-go for paying customers of SESI. It would be great if Mantra was doing architectural renders as good as VRay, but if you find your self in a spot you can't render such shot, it's most probably your fault of choosing wrong tool for a job. Why? Because you have a plethora of renderers available doing this kind of work great - exactly like in case of Maya (and no, Arnold is not builtin renderer of Maya, because a single license isn't enough for a job Maya is marketed for, it's merely a tease) - and if SESI would decide to scarify major Mantra's functionality in expense of faster rendering, it would break its deal with core customers and forces them to leave.
Both interior scene and pyro scene should have to be rendered motion blurred, displaced, heavily textured and with changing topology to make a valid point in the discussion. Even then previous comment applies: you might not have a performance of best market options, but you will have a decent working solution without +50K$ investment for a smallest render farm applicable in practice - and Houdini core market are companies having at least such farms.
Once buttom line is established (comparison to builtins), you may start thinking of an impact of programmable engine in your pipeline. Does it provide any value to you? Because if it doesn't, you should notice that programmability - the same as flexibility in general - doesn't come without a price! The more flexible renderer is, the slower it will crack common cases. This is a truth of life applicable for anything. The same goes for After Effect and Nuke, Final Cut and Avid, list goes on.
If Vray can render an animated and heavily textured scene - for whom irradiance caches or light caches aren't at any use - significantly faster than Mantra, this is a valid starting point of the discussion, specially if PRMan, 3delight or Arnold comes with the same results. Add to the bucket custom shaders, power of packed primitives, and we can start talking. If you're a freelance artist not carrying about those things, again, you should consider buying Redshift, it's out there, costs pennies, and you already did it for Maya or Max - not blaming ADSK for lack of fast light transport cached ray tracer.
From my experience, whenever I evaluate new renderer for a job (and I do it frequently for living), they are either not providing functionality customer looks for, or costs dozens of thousand of dollars and still comes with some limitations. I've recently advised Redshift for a constant-topology-light-geometry-show which seemed to suit it well, just to find out, that art director can't get the look he likes without lots of VEX code I know how to provide him in a day or two. Go figure!
I'm not saying Mantra doesn't need enhancements, this would be ridiculous for any renderer, I'm saying while it might be a slowest movie production renderer out there (which is not true btw, but let's say without supervision it doesn't play fast), it's still the most flexible (right after 3delight) and the cheapest one - specially teamed with Houdini for assembling and lighting. So with that in mind and considering any other builtin renderer can't even stand close:
Mantra is, in my opinion, one of the weak parts of Houdini
I totally disagree.
and I don't think anyone would disagree that improving it would be much appreciated.
while still supporting that specially from a freelance perspective (whom I would advice to use Redshift instead)
Szymon.
ps few words about Embree as a classical myth of CGI. Embree is fast compared to what? Really love this side effects of corpo marketing (the same was happening with OpenSubdiv btw). Any major renderer these days has already developed ray tracing core with acceleration structure at least as fast as Embree. Otherwise it's bummer with no future. The reason why PRMan or VRay, for example, has recently switched to Embree isn't mere performance, but maintenance. If Intel promises to support its development tightly synced with hardware advances this sounds like a great deal for software manufacturers forced to support high performance code on news hardware. Acceleration structure holds like 30% of mature renderer performance (unlike toy renderers which mostly shoots rays). Embree has to support all primitive types and advanced features of the mature renderer to be a good target to investigate, and even then making the mature Mantra code Embree dependent might slower it down for some time. Bottom line is, don't think that SESI team or Arnold team can't get the performance of Embree. They can do even more than that. At some point it's simply wise enough to push this efforts towards others focusing on your main expertise.
Similarly the same goes for TBB, which happens to be de facto current standard in VFX industry for multithreading architectures. There are actually much faster solutions out there. Just not supported by major hardware manufacturer - which doesn't look well for maintenance.
) - back in 2007).