On Nov 16, 2007 12:04 PM, Diederik van Lierop <mail@...2312...> wrote:
bulia byak wrote:
IMHO the key thing here is not just snapping to extensions of bbox, but _visualizing_ what it is that you snap to. In AI, it flashes the snap line when it snaps. We need to add infrastructure that would enable such displays when snapping, then smart guides will be easy.
Absolutely! It's also needed for the post-snap visualization that was discussed a few months ago, in which something lights up for a second at the point that has snapped. What would be a good starting point in the code to find out how such a thing would be drawn to the canvas? Do you already have passive elements like that, not allowing user interaction and disappearing after some time?
Of course. We have a number of classes that draw various helper things on the canvas. These classes handle proper canvas redraw (so you don't have to worry about that) and usually have methods for setting coordinates, colors, showing/hiding etc. Note that unlike regular objects, these helper thingies can use inverse color so they are visible on any background. But these classes do not do any user interaction; that is performed by upstream classes that uses these display classes. They also have no provisions for automatically disappearing after a time, that you will need to add in your own code. Here they are:
display/sp-ctrlline - draws a straight line, used by node tool bezier handles and by gradient tool for gradient lines
display/sodipodi-ctrrect - draws an upright rectangle, used for rubberband selection
display/sodipodi-ctrl - draws a number of various small fixed-size shapes, such as diamond, circle etc; used for knots and nodes
display/sp-ctrlquadr - draws an arbitrary quadrilateral, used for text selection
display/canvas-bpath - draws an arbitrary path with antialiasing, used for the red helper path in Node tool and for Pen tool, as well as for Tweak tool's circle (note: this one is slightly buggy, it leaves behind some dirt on the canvas; I want to switch it to using cairo but it's not yet possible due to incompatibility of buffer formats).
You can search the codebase for a lot of examples of using these things.