Preview: Hercules 3D Prophet 4500 with KYRO II (2/2) Tile Based Rendering ST Micro´s Kyro differs from traditional 3D chips from Ati, 3dfx and NVIDIA. Kyro and Kyro II are so called "Tiler". You speak of "Tile Based Rendering" here. SO what is a Tiler? This name stands for an architecture which helps to reduce the amount of data which is transfered over the card´s memory bus. Current 3D cards are memory bandwith limited. You can increase those limits by equipping the cards with faster but expensive memory. But the fact is that most of the memory bandwith is wasted with data which is not relevant for the final image.
Here´s an example. A person is walking through a room from the left to the right. Conventional chips do even render the pixel and objects which are covered by the person. Floors and other things behind the wall are also rendered very often. This causes many useless texture and Z operations with a lot of memory operations. You call that "Overdraw". A Tiler like Kyro and Kyro II is uses another way for rendering. A scene is separated in polygon groups. Each group is transfered to the Kyro chip which creates display list out of it. In addition, the chip does also separate the screen in many 32x16 pixel sized rectangles or Tiles. Every Tile is stored in an on-chip memory buffer and is rendered alone. A nice effect here is that this fits pretty well in shared memory systems... which means that Multi Chip Design should be no problem. The next step is to hinder overdraw. The chip "looks" which triangles and pixels can be seen in the final image. It drops all invisible pixels at this time. This is called "Hidden Surface Removal" and/or "Defered Texturing". This means that you do only need to read and shade textures which are really needed for the final image. You can take a look at the overdraw in games like Quake3 by using the option r_showtris 1.
The Tile´s data is written into the card´s memory after it is fully rendered. Then comes the next Tile. Another positiv feature in Kyro II it the image quality. All Tile operations are running in 32Bit Color Depth and at 32Bit precision - independant from the desktop or game resolution. The image is dithered down if 16Bit output is needed. What you will not find in this chip are Pixel Shader effects to create effects like Dot3 Bump Mapping. The card does only support Environmental Bump Mapping. BTW: Pixel Pipelines are not needed in this kind of chip because of the Tiling architecture. The Chip does support 8-Layer Multitexturing. Additional features are 2x and 4x FSAA as well as Hardware Motion Compensation DVD support. All this might help the chip to compete pretty well against NVIDIA´s GeForce 2 MX and ATi´s RADEON VE - even with a missing T&L engine. Conclusion You saw the theoretical part. Now we´ll have to see how the card and drivers (stability) perform in real games. In thery there is a lot of potential and the prices will be pretty low because of the use of cheap memory chips. Stay tuned for more details on the new card. Article-updates and first Prophet 4500 Benchmarks in the RIVA Station News! |
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Copyright: 09.03.2001 -
RIVA
Station 2001 - Lars Weinand URL of this Article: www.rivastation.com/prophet4500_prev_e.htm - If you want to link to it, please use this URL! :-) |
