Introduction

Considering the subjectiveness of remarks made throughout the years about graphics performance under RISC OS, I thought it was time to do some actual benchmarking.

The resulting program measures the performance of the most important and/or representative graphics operations (for a download, see below).

There are basically four main groups of operations :

• Lines. These contain very few pixels and are therefore both unrewarding and difficult to accelerate.
• Filled 'odd' shapes. These basically consist of many separate horizontal lines and are hardly ever used in the desktop.
• Rectangle fill and copy. These are, by far, the most used in the desktop, and are easy to accelerate. Rectangle copy is used for moving windows around, rectangle fill for clearing all sorts of backgrounds.
• Font plotting. Used to render almost all text within the desktop (although relatively few text editors use it). But almost impossible to accelerate.

Benchmarks have been run on RISC OS 4.39 and 6.20, using the native video system, ViewFinder, and VPod. Both Radeon and Rage 128 equipped ViewFinders were benchmarked, because RISC OS 6 does not support Radeon (although, in general, it is the fastest ViewFinder).

Results

There are some pretty surprising, and sometimes less surprising results :

• ViewFinder is consistently faster than VPod (1)
• VPod's performance drops horribly in high resolution modes (2)
• RISC OS 6.20 is consistently slower than RISC OS 4.39 (3)

(1) Except for font plotting in 256 colour modes, where the slightly slower ViewFinder frame buffer reads outweigh VPod's memory bandwidth problems.

(2) So much so, that in 1600 x 1200 modes, the performance difference with ViewFinder rises from between 1.5 and 5 times (256 colours) to 15 and 20 times (16M colours).

(3) Probably due to the extra overhead introduced by the new video hardware abstraction layer.

There are more remarkable little facts to be found, but these are left as an exercise for the reader ...

For a quick look at a few benchmark comparisons, go here :

VIDC (RISC OS 4.39) <--> VIDC (RISC OS 6.20)
VIDC (RISC OS 6.20) <--> VPod (RISC OS 6.20)
VPod (RISC OS 6.20) <--> ViewFinder Radeon (RISC OS 4.39)
VPod (RISC OS 6.20) <--> ViewFinder Rage 128 (RISC OS 6.20)
ViewFinder Rage 128 (RISC OS 4.39) <--> ViewFinder Radeon (RISC OS 4.39)
ViewFinder Rage 128 (RISC OS 4.39) <--> ViewFinder Rage 128 (RISC OS 6.20)

Signing off

If you want to have a go yourself, you can download the benchmark program here, along with the benchmark data files and a number of one-on-one comparison logs.

Research and this text by John Kortink.

First published 14 May 2011.