<IMG> and ISMAP (again)

Dave_Raggett (dsr@hplb.hpl.hp.com)
Tue, 1 Jun 93 15:38:27 BST

> My prefered scheme for selection of links in external objects is just send
> the x,y coordinates of the selection to the server and let it deal with
> it however is best. This is how the current selection stuff works for
> <IMG ISMAP>. This lets you backend with whatever you need (like maybe
> WAIS spatial indexing) without hardcoding anything in the client.

> This scheme has the advantages of being easy on the browser, simple to
> implement, low network overhead, it fits in with the existing HTTP
> protocol (even HTTP/0.9) and it's working today:

Just when I thought we had settled the matter!

Tim BL reminded me on the phone why this approach can't work in general.
Pixels only make sense for image data NOT for drawings, equations etc.
This means that we really do have to consider scaling the mouse click
coordinates. Tim suggests we use real numbers with 0 to 1.0 for each
axis (assuming square borders) with the upper left as (0, 0).

Dave Raggett