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Q&A with ATI's Chris Bentley on the Radeon Graphics Card
(DVD Info thanks to Arshad Rahman)

By Mike
Published: 10/25/2000

(Note: I had sent a series of questions to ATI about a month ago, before I reviewed the ATI Radeon graphics card hoping to publish this Q&A at the same time as the review of the Radeon (see related links below). I just received the answers yesterday afternoon but they will still be of interest. Thanks to ATI, Chris Bentley (and Arshad Rahman for the DVD info) for their input.)

Background:
I first got to know Chris back in 1997 when I received a prototype of the ATI RagePro graphics card for a preview here. I finally met him in person at Macworld NY this summer. He's a great guy and very enthusiastic about the Mac in general and the Radeon card in particular.

Chris is also the only guy I know that works the same insane hours I do - I can't count the number of times over the years I've either called him or received a call from him after midnight (and he's still at work!). I'd also like to say that Arshad Rahman has been very helpful with info on the Radeon's DVD features. Hat's off to these two great guys.

The following is a list of questions I sent before I had an actual Radeon card to review. In come cases the answers to performance questions are now shown in my reviews of the retail Radeon card and the previous BTO Radeon vs Rage128 Pro AGP review. (Links to these articles are below). Although there are some others I'd want to post now, these were sent before actually testing the card. I hope you find them of interest on understanding more about the Radeon's features and future software support.

1) What features of the RADEON are you most excited about?

Chris: Speed :-) Over twice the fill rate as the Rage128 Pro. After that it's the hardware TCL.

(TCL is Transform, Clipping and Lighting - see my Radeon Retail review Hardware Specs page for more info on these features)

2) What features of the RADEON do you feel provide the most advantage over other Mac graphics cards available now?

Chris: Currently, Cro-Mag Rally, Quake2, Quake3, Elite Forces, and any other upcoming Quake2, Quake3 engine games benefits from Hardware TCL. In our tests we're seeing TCL give us between 10-20% fps boost. Actually, the Quake3 engine uses the Hardware transform and clip, in test apps that use the Hardware lighting the speed boost can be substantially bigger.

Note: I later asked Chris about T&L support in RAVE: Chris: It doesn't. RAVE passes us coordinates in screen space, which means they've already been transformed by the app. There is no way in RAVE for the app to send us world coordinates which could be transformed in hardware.


3) I've heard the Radeon's Hyper-Z feature will increase performance.
Is this true and can you explain more about Hyper-Z?

Chris:   It's actually the bandwidth to the memory on the graphics card that is effectively increased through Hyper-Z which is a group of technologies that optimize the flow of information to the Z-buffer.This also provides a large part of the boost in Quake3 frame rates especially at higher resolutions.


4) Will the shipping OpenGL version and drives support all of the RADEON's features? (T&L, Hyper-Z).
If not, is that planned for future releases?

Chris:   The initial Apple OEM drivers support Hardware transform and clipping. The ATI retail drivers and the drivers that will be available in MacOS 9.1 add support for Hardware lighting. Hyper-Z is supported in all the drivers. We worked very closely with Apple to make the architectural changes needed to support Hardware TCL.


5) Have you compared performance of the AGP vs PCI versions?
If not, could you estimate what the performance differences may be?

Chris:   While we have done some preliminary tests we do not have enough results to make a general estimate of the final driver PCI performance.


6) Will the PCI RADEON be supported in pre-Beige G3 Macs?
What OS versions are supported?

Chris:   RADEON Mac Edition PCI work with any PCI Mac and we are planning for it to work with OS 8.6 and higher.


7) Will the current OS X Beta take advantage of any of the RADEON's Features?

Chris:   The OS X Beta has support for the ATI Rage 128 and Rage 128 Pro cards, but it does not yet support the RADEON. We currently have the RADEON up and running on MacOS X and it is looking really good, so RADEON support will definitely be there in version 1.0.


8) I hear the DVD playback on the RADEON has the lowest CPU cycle usage of any current graphics card - is this true?

Arshad:   ATI has had a long history of providing the lowest CPU utilization during DVD playback and we continue this with even more efficiency on the RADEON.

In order to understand how the RADEON offloads the CPU, we need to first understand how DVD is decoded on the Macintosh. The software player first loads the data from the DVD and parses this out into separate streams of video, audio, menu information etc. Some of these streams are then decoded in software such as the audio and CSS encryption. The video stream, which consists of raw macroblocks and motion vectors, is then passed to the ATI drivers for processing and display. Since the video decoding normally takes up the majority of the CPU cycles during a software decode, by offloading this to the RADEON, we can significantly reduce the CPU usage. Once this raw data is passed in, the RADEON then does a dezigzag of the DCT coefficients and performs an Inverse Discrete Cosine Transformation which converts the raw data from frequency space back into spatial data. (iDCT). Then depending on the type of macroblock, the motion compensation engine will combine multiple blocks from different buffers and locations and apply an error term and blend this into the destination buffer using subpixel accuracy. (Motion Compensation). We then take the resulting frames and use the back-end Overlay and Scaler to color convert the YUV4:2:0 data to RGB. This step also takes care of things like chroma interpolation, 4x4 tap filtering and scaling all in hardware to improve the quality of the final image. (Overlay+Scaler). The RADEON then hardware blends in a subpicture overlay which displays things like menu's and captioned text. (Subpicture). Lastly the hardware also applies hardware letterboxing to create the borders on the outside edges of letterboxed DVD's. One new feature of the RADEON which also helps tremendously in quality is "Adaptive Deinterlacing". What this does is scan an interlaced image and intelligently remove the 'feathering' artifacts that may be present which essentially gives you a progressive image without the loss in quality.

While some of these features may be present in competitors cards, such as a hardware overlay or motion compensation support, they do not present enough of a gain to provide full framerate software DVD playback. ATI is the currently only manufacturer on the Macintosh that provides all of the video decode and display features necessary to enable full screen, full framerate DVD playback with great quality without using a dedicated DVD decoder chip.


9) Do you have any 3D gaming performance test results to share?
(Note: See the review links below for test results)

Chris:   I saw on your page that users are starting to post RADEON results for Quake3 and Unreal Tournament. I think it's best if we just let users report their scores :-) However, I can just say that the scores that are being reported are exactly in line with what we're seeing in the lab.

(the Radeon review and the searchable FPS database here both have Radeon results-Mike.)


10) Have you tested the next release of Quake3 with the RADEON?
I hear it is to offer increased performance.

Chris:   I haven't tested the point release, but I talked to Graeme Devine at id, and given what he said they'd changed, I expect we'll see a really nice speed boost with it.


11) Is T&L supported in Mac Quake3 Arena? (now or planned for future updates)

Chris:   Quake2, Quake3, Elite Forces and any other Quake2 or Quake3 engine game uses Hardware tansform and clipping, the 'T' and 'C' in TCL. id's code does its own lighting calculations, so they don't use the Hardware lighting. These are all supported out of the box, and as I said above, we're seeing a 10-20% speed boost from Hardware TCL.


12) Will the RADEON's unique features be supported in future games?
If so which ones? Or will the OpenGL driver updates make these features available without game code modifications?

Chris:   The RADEON is able to support character skinning and tweening in Hardware; these are the features that fall under the "Charisma Engine." We have been working hard with the OpenGL ARB to write extensions to OpenGL so that game developers can access these features. At the last ARB meeting our vertex blending extension (skinning) was voted in as an official ARB extension. However, to use these features, game developers have to design their character animation engines with hardware assisted character animation in mind. This means that Hardware skinning and tweening are probably not going to be supported in any of this year's crop of games on the Mac. By next year, I think the focus of game developers will be shifting to MacOS X. So, we will definitely be adding support for all of the RADEON's unique features, hopefully by MacOS X 1.0.


13) Is the 16bit image quality better on the RADEON than the Rage128?
(Note: See the review links below for test result comments)

Chris:   It's basically the same. However, with the RADEON you do have the option of running Quake3 at 1024x768 at 32 bit color depth over twice as fast as a Rage128 Pro could run it (and of course considerably faster than any other card currently on the Mac :-).

(My Retail Radeon review linked below includes screenshots at 32bit color in several games.)


14) How does the 2D/Scrolling performance of the RADEON compare to the Rage128 Pro? (or other competitor's cards)
(Note: See the review links below for test results)

Chris:   The RADEON was designed with the mid to high end users in mind. Since 8bpp performance is no longer as important as 16bpp and 32bpp, the overall 8bpp graphics performance numbers are slightly slower than Rage128 Pro. However the 16bpp and 32bpp numbers are on par with Rage128 Pro, which is our focus. When examining individual subtest performance the RADEON is clearly faster than the Rage128 Pro across the board.


15) Will 3D apps like Lightwave 3D and Cinema 4D benefit from the RADEON?

Chris:   Absolutely, yes. We have worked quite closely with Matt Craig of Lightwave and they have had some of our early cards for testing. They have expressed very positive reactions to the RADEON running their app, so probably it's a good idea to ask them what they've seen. As for Cinema 4D, I just downloaded the Maxon Cinebench benchmark and ran it on the RADEON. While the benchmark seems somewhat CPU limited, the RADEON scores well above the Maxon software renderer, which apparently is not the case with all graphics cards these days.

(Note: See the Radeon retail review link below for a LW 3D v6 screenshot and performance comments)



Related Links:

  • ATI Radeon Mac Edition Review - the most complete review anywhere of the retail Radeon card with TV/video output. (Covering performance in 2D/3D/Games/Movies/DVD/TV Out/Specs/Software controls.) Includes comparisons to competitors cards.

  • ATI BTO Radeon Mac vs. Rage128 Pro - How the Radeon BTO graphics card compares to the standard Rage128 Pro version in performance.

  • Video Related Reviews/Articles - page listing all the video related articles here (Graphics cards, Video capture cards, DVD decoder reviews and tips/related articles).

  • Mac Video Card Performance Database - Searchable database of Mac video card/systems performance in Benchmarks (Cinebench 2000, Throughput, G4Timedemo) and Games (Quake 1, Quake2, Quake3, Unreal, Unreal Tournament, etc.). If you haven't already, Submit Your Results!


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