[Qgis-developer] show grid on map canvas (similiar to grid used in composer) - strategy?

[Etienne Tourigny]

On Fri, May 11, 2012 at 3:14 AM, Martin Dobias <wonder.sk at gmail.com> wrote:
> On Fri, May 11, 2012 at 12:40 AM, Etienne Tourigny
> <etourigny.dev at gmail.com> wrote:
>>> For me a grid is a good candidate to be implemented as another type of
>>> decoration (currently there is north arrow, scale bar and copyright
>>> label). A decoration is drawn on top of the map when map rendering has
>>> finished. And symbology can still be applied when drawing grid as a
>>> decoration.
>>
>> Hmm... symbology applied to what?
>>
>> Nathan's suggestion to make it a layer to be able to style it makes
>> sense. Any way we can use the symbology interface on a map decoration?
>> Can we re-use existing widgets for this, or just a waste or time
>> instead of designing a new widget?
>
> It is fairly easy to provide a GUI where users would select/modify the
> symbol for drawing grid lines (all necessary widgets are in qgis_gui
> library - QgsSymbolV2SelectorDialog, QgsSymbolV2PropertiesDialog). For
> drawing itself you only have to construct a QgsRenderContext instance
> and issue calls to QgsLineSymbolV2::renderPolyline(...). Before first
> render call make sure to initialize the symbol with startRender() and
> at the end stopRender(). To get screen coordinates from map
> coordinates there is QgsMapToPixel utility class.
>

Thanks Martin, this is great to know.  Existing code (composer grid)
does not seem use this infrastructure.

Would it make sense to create a new qgisgui element (or other class)
to deal with grids, and re-use this code in the composer?
Or perhaps just draw in the composer whatever grid(s) have been
defined by the user in the main canvas?

Are there any documentation/examples on using qgisgui elements, other
than the api?


Regards,
Etienne



> Regards
> Martin