Tile Based Rendering and Accelerated 3D

ChickenHead writes "AnandTech has put together a review of the Hercules 3D Prophet 4500 based on the new Kyro II chip from STMicro. What's unique about this particular chip is that it uses a Tile-based Rendering Architecture which results in a much greater rendering efficiency than conventional 3D rendering techniques. It is so efficient in fact, that the $149 Kyro II card clocked at 175MHz is able to outperform a GeForce2 Ultra with considerably more power and around 3X the cost of the Kyro II card. With games not able to take advantage of the recently announced GeForce3's feature set, the Kyro II may be a cheap solution to tide you over until the programmable GeForce3 GPU becomes a necessity." A very readable and interesting summary and an interesting technology and a potentially extremely cool video card.

Comments

A little bit hyped maybe?

[evanbd]

If the poster had read the benchmarks, it would be obvious that the case is not so cut and dry. The card wins at some things, loses at others. It loses to the GF2GTS in some benchmarks, and beats the GF2 Ultra in others. A very cool card, and worlds beyond anything in its price range, however. This should do very good things to the low price range performance market as a whole, by pushing down other prices and by providing a cool new technology.

Tile-based rendering

[Mumbly_Joe]

Tile-based rendering only outperforms other types of rendering on certain types of tests.

Tile-based rendering's big benefit it that is reduces overdraw to 0; that is, each opaque pixel on the screen is drawn exactly once. Performance for certain types of scenes is spectacular.

Dreamcast uses this, as well as many of Sega's arcade systems (HOTD2, for instance), which use the same PowerVR2 rendering system.

Where tile-based rendering falls down, however, is for scenes that contain a large amount of alpha-blended areas. Alpha-blended areas in today's hardware are necessarily drawn multiple times, from back-to-front, to accomplish transparency effects. Having to draw the pixel several times nullifies the zero-overdraw benefit of tile rendering. Since most tile-rendering systems trade fill-rate for zero overdraw, cards with insufficient fill rate for large alpha areas (read: all of them) fall down on large, alpha blended polygons. You can see this in House of the Dead 2 when fighting the Hierophant; if you get enough water splash effects on the screen, the frame rate chokes.

Tile rendering works extremely well for areas that are opaque, or use only small alpha-blended areas. It's getting better; it's just not perfect yet.

Mumbly Joe

Tile-based rendering, strenghs and weaknesses

[Olivier Galibert]

The simple idea behind tile-based rendering is to divide the screen into square patches (8x8 or 16x16 usually) and, for each patch, find which of the triangles intersect the patch, do a quick depth sort to detect complete occlusions, and draw.

There is a good article on it, as applied to the powervr (which is using the same kind of architecture) at http://www.ping.be/powervr/PVRSGRendMain.htm. As others already said, you can see the results on the Dreamcast, or on the arcade version, the Naomi.

The strenghts are obvious:

• Lower fillrate required because of the per-petch occulted triangles elimination
• The currently-rendered tile memory can be on-die, L1-grade, releasing the bandwitch for texture reading

The weaknesses are a little less obvious:

• Rendering start delayed because it requires having all the triangles available. Can be somewhat hidden by multi-buffering
• Alpha-blending slows things down hard, because it increases the required fillrate very fast, and these cards are designed with a lower fillrate in mind
• There is no Z-buffer anymore (at least at peak speed, it's not copied back to the main memory), and we know that the 3D programmers love to do tricks with the Z-buffer

As a result, these cards are nice, but mostly represent another set of tradeoffs, not necessarily a revolution.

OG.