Subject: General Tech | March 22, 2018 - 12:37 PM | Alex Lustenberg
Tagged: winml, vive pro, video, Tobii, SBX, rtx, qualcomm, podcast, pny, MyDigitalSSD, logitech, htc, G560, G513, dxr, CS900, corsair, caldigit, AX1600i
PC Perspective Podcast #492 - 03/22/18
Join us this week for MyDigitalSSD, CalDigit Tuff Drive, and more!
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Hosts: Jim Tanous, Jeremy Hellstrom, Josh Walrath
Peanut Gallery: Alex Lustenberg
Program length: 1:08:16
O Rayly? Ya Rayly. No Ray!
Microsoft has just announced a raytracing extension to DirectX 12, called DirectX Raytracing (DXR), at the 2018 Game Developer's Conference in San Francisco.
The goal is not to completely replace rasterization… at least not yet. This effect will be mostly implemented for effects that require supplementary datasets, such as reflections, ambient occlusion, and refraction. Rasterization, the typical way that 3D geometry gets drawn on a 2D display, converts triangle coordinates into screen coordinates, and then a point-in-triangle test runs across every sample. This will likely occur once per AA sample (minus pixels that the triangle can’t possibly cover -- such as a pixel outside of the triangle's bounding box -- but that's just optimization).
For rasterization, each triangle is laid on a 2D grid corresponding to the draw surface.
If any sample is in the triangle, the pixel shader is run.
This example shows the rotated grid MSAA case.
A program, called a pixel shader, is then run with some set of data that the GPU could gather on every valid pixel in the triangle. This set of data typically includes things like world coordinate, screen coordinate, texture coordinates, nearby vertices, and so forth. This lacks a lot of information, especially things that are not visible to the camera. The application is free to provide other sources of data for the shader to crawl… but what?
- Cubemaps are useful for reflections, but they don’t necessarily match the scene.
- Voxels are useful for lighting, as seen with NVIDIA’s VXGI and VXAO.
This is where DirectX Raytracing comes in. There’s quite a few components to it, but it’s basically a new pipeline that handles how rays are cast into the environment. After being queued, it starts out with a ray-generation stage, and then, depending on what happens to the ray in the scene, there are close-hit, any-hit, and miss shaders. Ray generation allows the developer to set up how the rays are cast, where they call an HLSL instrinsic instruction, TraceRay (which is a clever way of invoking them, by the way). This function takes an origin and a direction, so you can choose to, for example, cast rays only in the direction of lights if your algorithm was to, for instance, approximate partially occluded soft shadows from a non-point light. (There are better algorithms to do that, but it's just the first example that came off the top of my head.) The close-hit, any-hit, and miss shaders occur at the point where the traced ray ends.
To connect this with current technology, imagine that ray-generation is like a vertex shader in rasterization, where it sets up the triangle to be rasterized, leading to pixel shaders being called.
Even more interesting – the close-hit, any-hit, and miss shaders can call TraceRay themselves, which is used for multi-bounce and other recursive algorithms (see: figure above). The obvious use case might be reflections, which is the headline of the GDC talk, but they want it to be as general as possible, aligning with the evolution of GPUs. Looking at NVIDIA’s VXAO implementation, it also seems like a natural fit for a raytracing algorithm.
Speaking of data structures, Microsoft also detailed what they call the acceleration structure. Each object is composed of two levels. The top level contains per-object metadata, like its transformation and whatever else data that the developer wants to add to it. The bottom level contains the geometry. The briefing states, “essentially vertex and index buffers” so we asked for clarification. DXR requires that triangle geometry be specified as vertex positions in either 32-bit float3 or 16-bit float3 values. There is also a stride property, so developers can tweak data alignment and use their rasterization vertex buffer, as long as it's HLSL float3, either 16-bit or 32-bit.
As for the tools to develop this in…
Microsoft announced PIX back in January 2017. This is a debugging and performance analyzer for 64-bit, DirectX 12 applications. Microsoft will upgrade it to support DXR as soon as the API is released (specifically, “Day 1”). This includes the API calls, the raytracing pipeline resources, the acceleration structure, and so forth. As usual, you can expect Microsoft to support their APIs with quite decent – not perfect, but decent – documentation and tools. They do it well, and they want to make sure it’s available when the API is.
Example of DXR via EA's in-development SEED engine.
In short, raytracing is here, but it’s not taking over rasterization. It doesn’t need to. Microsoft is just giving game developers another, standardized mechanism to gather supplementary data for their games. Several game engines have already announced support for this technology, including the usual suspects of anything top-tier game technology:
- Frostbite (EA/DICE)
- SEED (EA)
- 3DMark (Futuremark)
- Unreal Engine 4 (Epic Games)
- Unity Engine (Unity Technologies)
They also said, “and several others we can’t disclose yet”, so this list is not even complete. But, yeah, if you have Frostbite, Unreal Engine, and Unity, then you have a sizeable market as it is. There is always a question about how much each of these engines will support the technology. Currently, raytracing is not portable outside of DirectX 12, because it’s literally being announced today, and each of these engines intend to support more than just Windows 10 and Xbox.
Still, we finally have a standard for raytracing, which should drive vendors to optimize in a specific direction. From there, it's just a matter of someone taking the risk to actually use the technology for a cool work of art.
If you want to read more, check out Ryan's post about the also-announced RTX, NVIDIA's raytracing technology.
Subject: Graphics Cards | March 19, 2018 - 01:00 PM | Ryan Shrout
Tagged: rtx, nvidia, dxr
The big news from the Game Developers Conference this week was Microsoft’s reveal of its work on a new ray tracing API for DirectX called DirectX Raytracing. As the name would imply, this is a new initiative to bring the image quality improvements of ray tracing to consumer hardware with the push of Microsoft’s DX team. Scott already has a great write up on that news and current and future implications of what it will mean for PC gamers, so I highly encourage you all to read that over before diving more into this NVIDIA-specific news.
- For those you that might need a history lesson on ray tracing and its growth, check out this three-part series that ran on PC Perspective as far back as 2006!
- Ray Tracing and Gaming - Quake 4: Ray Traced Project
- Rendering Games with Raytracing Will Revolutionize Graphics
- Ray Tracing and Gaming - One Year Later
Ray tracing has been the holy grail of real-time rendering. It is the gap between movies and games – though ray tracing continues to improve in performance it takes the power of offline server farms to render the images for your favorite flicks. Modern game engines continue to use rasterization, an efficient method for rendering graphics but one that depends on tricks and illusions to recreate the intended image. Ray tracing inherently solves the problems that rasterization works around including shadows, transparency, refraction, and reflection. But it does so at a prohibitive performance cost. But that will be changing with Microsoft’s enablement of ray tracing through a common API and technology like what NVIDIA has built to accelerate it.
Alongside support and verbal commitment to DXR, NVIDIA is announcing RTX Technology. This is a combination of hardware and software advances to improve the performance of ray tracing algorithms on its hardware and it works hand in hand with DXR. NVIDIA believes this is the culmination of 10 years of development on ray tracing, much of which we have talked about on this side from the world of professional graphics systems. Think Iray, OptiX, and more.
RTX will run on Volta GPUs only today, which does limit usefulness to gamers. With the only graphics card on the market even close to considered a gaming product the $3000 TITAN V, RTX is more of a forward-looking technology announcement for the company. We can obviously assume then that RTX technology will be integrated on any future consumer gaming graphics cards, be that a revision of Volta of something completely different. (NVIDIA refused to acknowledge plans for any pending Volta consumer GPUs during our meeting.)
The idea I get from NVIDIA is that today’s RTX is meant as a developer enablement platform, getting them used to the idea of adding ray tracing effects into their games and engines and to realize that NVIDIA provides the best hardware to get that done.
I’ll be honest with you – NVIDIA was light on the details of what RTX exactly IS and how it accelerates ray tracing. One very interesting example I was given was seen first with the AI-powered ray tracing optimizations for Optix from last year’s GDC. There, NVIDIA demonstrated that using the Volta Tensor cores it could run an AI-powered de-noiser on the ray traced image, effectively improving the quality of the resulting image and emulating much higher ray counts than are actually processed.
By using the Tensor cores with RTX for DXR implementation on the TITAN V, NVIDIA will be able to offer image quality and performance for ray tracing well ahead of even the TITAN Xp or GTX 1080 Ti as those GPUs do not have Tensor cores on-board. Does this mean that all (or flagship) consumer graphics cards from NVIDIA will includ Tensor cores to enable RTX performance? Obviously, NVIDIA wouldn’t confirm that but to me it makes sense that we will see that in future generations. The scale of Tensor core integration might change based on price points, but if NVIDIA and Microsoft truly believe in the future of ray tracing to augment and significantly replace rasterization methods, then it will be necessary.
Though that is one example of hardware specific features being used for RTX on NVIDIA hardware, it’s not the only one that is on Volta. But NVIDIA wouldn’t share more.
The relationship between Microsoft DirectX Raytracing and NVIDIA RTX is a bit confusing, but it’s easier to think of RTX as the underlying brand for the ability to ray trace on NVIDIA GPUs. The DXR API is still the interface between the game developer and the hardware, but RTX is what gives NVIDIA the advantage over AMD and its Radeon graphics cards, at least according to NVIDIA.
DXR will still run on other GPUS from NVIDIA that aren’t utilizing the Volta architecture. Microsoft says that any board that can support DX12 Compute will be able to run the new API. But NVIDIA did point out that in its mind, even with a high-end SKU like the GTX 1080 Ti, the ray tracing performance will limit the ability to integrate ray tracing features and enhancements in real-time game engines in the immediate timeframe. It’s not to say it is impossible, or that some engine devs might spend the time to build something unique, but it is interesting to hear NVIDIA infer that only future products will benefit from ray tracing in games.
It’s also likely that we are months if not a year or more from seeing good integration of DXR in games at retail. And it is also possible that NVIDIA is downplaying the importance of DXR performance today if it happens to be slower than the Vega 64 in the upcoming Futuremark benchmark release.
Alongside the RTX announcement comes GameWorks Ray Tracing, a colleciton of turnkey modules based on DXR. GameWorks has its own reputation, and we aren't going to get into that here, but NVIDIA wants to think of this addition to it as a way to "turbo charge enablement" of ray tracing effects in games.
NVIDIA believes that developers are incredibly excited for the implementation of ray tracing into game engines, and that the demos being shown at GDC this week will blow us away. I am looking forward to seeing them and for getting the reactions of major game devs on the release of Microsoft’s new DXR API. The performance impact of ray tracing will still be a hindrance to larger scale implementations, but with DXR driving the direction with a unified standard, I still expect to see some games with revolutionary image quality by the end of the year.