The fact that guide improvement is one of the projects accepted by Google Summer of Code projects is really good news! Guides are particularly helpful features in illustration programs.
I thought it'd be a good time to write up some of the possibilities of guides. I doubt anyone can implement any of it anytime soon (certainly not before the current GSOC project is finished), but it might be helpful to keep these in mind to not close off future possibilities in the definitions or the GUI.
Write-up here:
http://wiki.inkscape.org/wiki/index.php/Active_guide_proposals
As you can see, features I think will can be particularly useful are:
- Symmetry guides: by simply toggling them on and off, you can enter an improved "mirror" mode. Helpful for everything from complicated technical illustrations to just drawing some vases
in some corner.
- Convergence points: this could be a mere feature of a more general "guide point". When drawing straight lines, the lines would "snap" to the direction of one of the active convergence points. Anyone who's ever tried to illustrate a building in 2D or 3D should know how helpful this would be (because the vanishing points can be so far away from the rest of the drawing that it's really no fun to look for them every time).
- More generally, guide points and guidelines could have various properties activated. Guidelines with "orthogonal" and "parallel" properties activated, for example, would cause straight lines drawn to snap in a direction orthogonal/parallel to said guidelines. Very helpful for geometric drawing.
- Then there are kinematic templates (by Richard Fung). I don't know why this still hasn't been ported to any of the major open source image programs, but in Inkscape, they would be great fun when combined with the calligraphy tool.
I can work more on the GUI proposal in the meantime, but I'm not sure where to go from here, so comments are welcome.