On Tuesday, May 11, 2010 at 15:34:23 (+0100) Andrew Ross writes: > > I've been trying to tidy up some of the inconsistencies between different > interactive drivers on plplot. The xwin, tk, qtwidget and xcairo drivers > now all more or less have consistent handling of plGetCursor as far as is > possible. > > The big outstanding issue in terms of the interactive examples in plplot > is the xor mode which is used by xwin and tk to draw then remove lines > while interactively selecting region in example 20 (also tested in > example 1). Now these days it seems that this is not the preferred way > of doing such things. Qt for example dropped support for xor mode. It > does provide alternative ways of doing things like selection using > QRubberBand. One problem is that using xor does not guarantee you a line > that is clearly visible, depending on the background image or graph. > > As a stop-gap measure we could just not draw the lines for devices which > don't support xor mode but do support plGetCursor. I've done this for > the octave examples and it works, but it isn't ideal. > > I wonder if it would be better to have a plplot function to select a > rectangle (something like the octave plrb) which could delegate the > drawing of the rectangle to the driver via an escape function? The > drivers could then handle it in the most appropriate way. For the low > level xwin driver this would be via xor, for higher level drivers > such as qtwidget it might use library specific functions. I guess we > would leave xor mode for those drivers which support it, but > depreciate it over time. > > Of course, if anyone has any bright ideas how to implement something > like xor mode for some of the other drivers that would be good.
I agree, xor mode sucks big time (due to the line occasionally becoming invisible). On a recent project, I implemented a plot overlay capability for drawing a ruler between two interactively selected points, with coordinates plotted in world coordinates. The basic flow was as follows: - set up all the event bindings to have the facility act as desired - every time the mouse moves: o force an expose event.. this blits the backing pixmap to the screen o turn off plot buffer & backing pixmap writing o draw your desired overlay & register it with your redraw facility (you must commandeer redraw for this to work) o turn back on plot buffer & backing pixmap writing - restore original bindings when custom drawing mode is terminated The turning off of the plot buffer & backing pixmap writing requires some rather evil direct manipulation of the contents of the PLStream and XwDev structs.. an API for this would be hugely better. As well as a demo. One can dream.. anyway maybe some food for thought. -- Maurice LeBrun ------------------------------------------------------------------------------ _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
