QTiles: implement option to not render empty tiles

[F-JJTH]

This patch give the option for users like me to not render 100% transparent tiles.

Example:
Without my patch, I have a raster covering France and a raster covering Japan, I choose 'Full extent' export and zoom 8-14 and transparency 255.
QTiles will generate 18 millions tiles where almost 80% are unused because I have no raster for Germany, Roumania, Russia, India, China..... so QTiles wille create 100% transparent PNG for those countries

With my patch, when the user uncheck the "Render empty tiles" checkbox, only 4 millions of tiles will be generated because my patch skip all countries where there is no raster.

The technique to achieve this is very simple: before adding the tile to the "tiles cues" I check if at least one of raster extent intercept the tile extent.

I think this patch is also partly in relation to #56

Best regards,

[simgislab]

Hi F-JJTH, thanks! We're reviewing your patch, hope to have new release soon.

[F-JJTH]

Hi,
Great ! For information, QGis provides QTiles 1.5.0 (https://plugins.qgis.org/plugins/qtiles/) while your repository hold 1.5.1 and you are going to release a new version soon (1.5.2 I guess). It would be nice to tell QGis to updates their QTiles version as soon as you release a new version.
However I have absolutely no idea about the update process for QGis plugin, so maybe it is not of your responsibility.

[simgislab]

we will release 1.5.1, version we work on here is master, version at QGIS hub is the latest release

[F-JJTH]

Alright, thanks you. I plan to contribute again in order to make QTiles multi-threading ;-)

[simgislab]

sounds great!