martin: Unfortunately I'm not in a position to make any useful comment about RISCOS Ltd's supposed vector icons idea because I know nothing of it myself, and have not been involved with it in any way. I've heard the odd rumour about this idea, as have others, but I know nothing concrete.
However, what I *can* say on this subject is that, if it were to happen, the RISC OS 5 icons would be in an ideal position to take advantage of it, because they were all designed in ArtWorks from the outset. It would be simplicity itself to derive a new set of vector-based OS icons from my current ArtWorks sources; and alpha-blending would also presumably work, too.
This would also be a far more sensible and realistic proposition than starting from scratch with a new vector set based on, say, the existing RISC OS 4 icons or any other theme. Believe me when I say that the creation of a set of consistent, good-looking, carefully thought out desktop icons is not a trivial process! Even with the advantages of ArtWorks and the benefits it brings (e.g. the ability to use layers to copy and overlay elements and create consistency between icons), the creation of the RO5 icon set took a very considerable amount of time and effort. Obviously it would have taken a lot /more/ time and effort if I'd used a bitmap editor rather than a vector drawing package but, even so, quite a lot of bitmap post-editing was required to create the TV-resolution versions and other things. These tall-pixel sprites do present a bit of a problem with respect to vector rendering, but hopefully not an insurmountable one.
The window tools proved to be pretty demanding and required a lot of work, but are also vector-based and were created in ArtWorks, though they do make use of bitmaps to create the various textures. I agree in principle that it should be possible to make them scriptable in some way, though in reality the way they're plotted by the Wimp is one of the major problems that would need to be overcome.
People have complained and disagreed about the window tools more than any other aspect of the RISC OS 5 appearance, but leaving aside the issue of whether you like my designs or not, it must be recognised that the designer is very much restricted in terms of what he can do by limitations and shortcomings inherent to the Wimp's handling of window furniture. To improve the situation in any genuinely useful way would require a complete rewrite of this part of the Wimp itself. You can get around some of the issues by some fudging (e.g. the need for there to be a pixel border separating all tools can be circumvented, but only by making ugly compromises in other ways, such as having open-ended title bars that don't look finished off properly - as in those Mac OS X rip-off window tools, which I personally dislike very much). There's plenty of other things that you just can't do, though, like using lots of colours to improve shading etc., and there are bugs that you have to work around too, which cause problems and compromises of their own.
What I'd like to see is a fully customisable way of creating window tools in which the symbols for the tools could be defined independently of the backgrounds, and the backgrounds themselves could be more flexible. If the window tools were to become vector-based, then it should certainly be easier to achieve this.