wxgui: add monitor calibrate option to prefs
|Reported by:||hamish||Owned by:|
currently the wxGUI offers a 1:xxxxx map scale option in the status bar of the Map Display window. By definition this is the ratio of the distance (in map units) on the ground to the distance (in map units) on the rendered display.
Without knowing the monitor size + resolution the currently displayed value seems to just be like region_distance/number_of_pixels. So it's missing being multiplied by a
pixels_per_meter factor (if map units were in meters..).
X11 and I suspect OSX & MS Windows provide some info about the monitor, but in the past those reported values have been quite unreliable. Maybe it is a little better now and could be used for setting a seed value?
I propose to do as GIMP and Inkscape do, and offer a calibration tool in the Preferences menu's "Display" setting tab. Then we know the DPI to map-units conversion factor specific to the user's screen resolution and monitor size, and after calibration they can trust the scale shown in the info bar. Either that or remove the currently erroneous option altogether.
I've just looked at the version in Inkscape 0.48.1 and it seems quite nice and easy to use. Inkscape is written using wx(C++) but maybe there is still some pre-fab code in there we could quickly adapt?
gv program uses another way, in its State->Setup options it lets you define "Screen size (mm): _ x _"
note that this isn't an issue for ps.map, because we already know the exact dimensions of the paper sizes.