Videologic Vivid!XS Kyro II Review

TV Out

The Vivid! XS features an S-Video output jack for TV Output, although you also get a S-Video to Composite converter cable with the Vivid! XS to enable the use of TV Output should a S-Video connection be unavailable.

Tile Based Deferred Rendering

Before moving into further details about the Vivid! XSí performance it would be wise to talk a bit about Tile Based Deferred Rendering. Probably the 2 most important factors in determining a Graphics cards performance would be that of effective Memory bandwidth & Overdraw.

Memory bandwidth. In recent times we've seen that Graphics Cards have become increasingly memory bandwidth limited. Last year we had the Geforce 2 experiencing this & this year we have the Geforce 2 MX 2/400s in a similar situation. ATI have developed Hyper-Z in the Radeon to help alleviate this problem, while the Geforce 3 has Z-Occlusion Culling for similar reasons. Memory bandwidth is the power needed to render your Games (Or other 3D accelerated Applications), the greater your bandwidth, the greater the expected performance. In a way it's much like your Internet connection - A person with Cable is going to have a whole lot more bandwidth at his disposal than someone with a V90 Dial-up connection.

Overdraw. This wastes memory bandwidth & processing power rendering pixels that arenít visible. As games are becoming more complex the level of overdraw is increasing rather drastically, hence the amount of bandwidth required (& more importantly, wasted) is also increasing at a similar rate. Some may well argue that developers are to blame for this problem (The Quake Engines are semi-renowned for their low amounts of overdraw) but thatís not really an easy to solve problem.

Tile Based (Deferred) Rendering. The Kyro2 divides the screen into multiple tiles (Hence why itís called Tile based rendering) of 32x16 pixels. The number of tiles created varies with screen resolution, e.g. 1536 tiles are created at 1024*768, while only 600 tiles are at 640*480. Each of these tiles is then tested by the On-chip Tile-Buffer to determine whether or not the pixels are visible. Should they not be visible then they are disregarded & nothing more need be done with them in the rendering process. The diagram beneath from the PowerVR TBR Whitepaper illustrates this rather nicely.

As you can see, the tile-based solution inevitably only renders foreground objects while traditional 3D renderers are also rendering non-visible background objects as well.

The Deferred part refers to texturing. Only once pixels have been verified as being visible by the On-chip Tile-Buffer are textures applied to them. As such textures arenít loaded unless they are going to be seen. This saves memory bandwidth as a result, which aids overall performance.

 



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