When path tracing works, it is much, much, MUCH simpler and vastly saner algorithm than those stacks of 40+ complicated rasterization hacks in current rasterization based renderers that barely manage to capture crude approxinations of the first indirect light bounces. Rasterization as a rendering model for realistic lighting has outlived its usefulness. It overstayed because optimizing ray-triangle intersection tests for path tracing in hardware is a hard problem that took some 15 o 20 years of research to even get to the first generation RTX hardware.
>When path tracing works, it is much, much, MUCH simpler and vastly saner algorithm than those stacks of 40+ complicated rasterization hacks in current rasterization based renderers that barely manage to capture crude approxinations of the first indirect light bounces.
It's ironic that you harp about "hacks" that are used in rasterization, when raytracing is so computationally intensive that you need layers upon layers of performance hacks to get decent performance. The raytraced results needs to be denoised because not enough rays are used. The output of that needs to be supersampled (because you need to render at low resolution to get acceptable performance), and then on top of all of that you need to hallu^W extrapolate frames to hit high frame rates.
And you still need rasterization for ray traced games (even "fully" path traced games like Cyberpunk 2077) because the ray tracing sample count is too low to result in an acceptable image even after denoising. So the primary visibility rendering is done via rasterization (which has all the fine texture and geometry detail without shading), and the ray traced (and denoised) shading is layerd on top.
This combination of techniques is actually pretty smart: Combine the powers of the rasterization and ray tracing algorithms to achieve the best quality/speed combination.
The rendering implementation in software like Blender can afford to be primitive in comparison: It's not for real-time animation, so they don't make use of rasterization at all and do not even use denoising. That's why rendering a simple scene takes seconds in Blender to converge but only milliseconds in modern games.
For primary visibility, you don't need more than 1 sample. All it is is a simple "send ray from camera, stop on first hit, done". No monte carlo needed, no noise.
On recent hardware, for some scenes, I've heard of primary visibility being faster to raytrace than rasterize.
The main reasons why games are currently using raster for primary visibility:
1. They already have a raster pipeline in their engine, have special geometry paths that only work in raster (e.g. Nanite), or want to support GPUs without any raytracing capability and need to ship a raster pipeline anyways, and so might as well just use raster for primary visibility.
2. Acceleration structure building and memory usage is a big, unsolved problem at the moment. Unlike with raster, there aren't existing solutions like LODs, streaming, compression, frustum/occlusion culling, etc to keep memory and computation costs down. Not to mention that updating acceleration structures every time something moves or deforms is a really big cost. So games are using low-resolution "proxy" meshes for raytracing lighting, and using their existing high-resolution meshes for rasterization of primary visibility. You can then apply your low(relative) quality lighting to your high quality visibility and get a good overall image.
Nvidia's recent extensions and blackwell hardware are changing the calculus though. Their partitioned TLAS extension lowers the acceleration structure build cost when moving objects around, their BLAS extension allows for LOD/streaming solutions to keep memory usage down as well as cheaper deformation for things like skinned meshes since you don't have to rebuild the entire BLAS, and blackwell has special compression for BLAS clusters to further reduce memory usage. I expect more games in the ~near future (remember games take 4+ years of development, and they have to account for people on low-end and older hardware) to move to raytracing primary visibility, and ditching raster entirely.
As a sibling post already mentioned, rasterization based hacks are incapable of getting as accurate lighting as path tracing can, given enough processing time.
I will admit that I was a bit sly in that I omitted the word "realtime" from the path tracing part of my claim on purpose. The amount of denoising that is currently required doesn't excite me either, from a theoretical purity standpoint. My sincere hope is that there is still a feasible path to a much higher ray count (maybe ~100x) and much less denoising.
But that is really the allure of path tracing: a basic implementation is at the same time much simpler and more principled than any rasterization based approximation of global illumination can ever be.
This doesn't hold at all. Path tracing doesn't "just work", it is computational infeasible. It needs acceleration structures, ray traversal scheduling, denoisers, upscalers, and a million other hacks to work any close to real-time.
