It is already possible to add (and remove) guides one
at a time by clicking on the rulers.
What I am suggesting is to provide a menu item
View, New Guide...
to allow users to add a guide using the keyboard.
this is good for both users that need it for
accessibility and ordinary users that want greater
accuracy.
This feature should be easy enough to add as it
essentially just provind an alternative interface to
exisiting funtionality.
New Guide would display a dialog something like this
New Guide
Position [ 50] [ pixels [v] [] Repeat
Direction
() Horizontal
() Vertical
[Reset] [Cancel ]
[ OK ]
Ideally the object labelled pixels would be a drop down
box that allowed users to choose various unit types
including centimetres(cm) milimeters (mm), percentages,
pixels, etc.
It might also be worthwhile to to include a [] Repeat
option that would add a guide every N pixels.
Similarly it might be useful to include an option to
add a guide to both Horizontal and Vertical at the same
time.
The position box could be prefilled with a default
value (the midpoint of the image, or 1/10th of the
image for example).
Clear All would simply clear all the guides from the
image without asking any additional questions (action
would be undoable).
I expect this would be done as an internal extension.
If Inkscape had a scripting interface it could be done
using that but the Position input widget would need to
check that the position is not out of bounds and
ideally that should be done on the fly rather than just
giving the user and error when they hit OK. (I've
implemented pretty much this same functionality as a
Gimp script and it sucks not to be able to check the
input on the fly, so I'd have to write a fully fledged
plugin with its own interface to do it).
It should be possible to do many things using only the
keyboard. In some cases it is particularly useful to
be able to specify the coordiantes when adding or
drawing something.
The scripting API will very likely provide a way to do
this but certain things are definately worth providing
for all users.
I have marked the priority of this as Low (3).
Also it would be fun if in new guide dialog you will be
able to enter the angle on wih new guide is to be rotated.