[Feature] Load layers as single WMS layer

[mind84]

Allows to load project layers as single WMS Layer.

Feature description:

This development is intended to increase LZM performance when large projects containing many layers are loaded.
This option is presented as alternative to classic mode, and users should be able to switch from one mode to another by acting on the Lizmap plugin configuration.

Despite the performance improvements, some functionality are no longer available when a single layer is loaded, i.e.:

• acting on the opacity of a single layer
• define the image type of the single layer
• turning off a layer is no longer immediate, but the system must reload the entire image
• excluding cached map layers from the single WMS image breaks the layer tree order

Logics in detail

• General
  I used the same classic layer map instance for loading the single WMS image. The advantage is that you can inherit the general configuration of the main map without duplicating it. If the main map useTileWms property is true , then the single WMS layer is loaded as TileWMS.

• Baselayers
  All external baselayers and cached ones (WMTS) comes independently. Only Lizmap baselayers (i.e. loaded by QGIS server) are loaded in the singleWMS layer together with map layers.

• Cached map layers
  All cached map layers (i.e. tiled WMTS layers) comes independently

• Filtering features/ filtering by legend
  These two functionalities (alone or in combination) works also with single WMS layer

Consideration about layers order

As said, if some layer are tiled then they will be not included in the single WMS. This unfortunately has a very high chance of breaking the layers map order and there is no way (at least IMHO) to avoid this. I'll explain by an example the current layer order logic when single WMS is turned on.

Take for example the following layertree:

Layer tree
 Map layers
   Layer A -> classic layer, included in single WMS
   Layer B -> classic layer,  included in single WMS
   Layer C -> cached WMTS layer, excluded from single WMS
   Layer D -> classic layer,  included in single WMS
   Layer E -> cached WMTS layer, excluded from single WMS
 Baselayers
   OpenStreetMap (or Bing or whatever) -> excluded from WMS
   BaseLayer E -> Lizmap layer, included in single WMS

On the map, the real order is:

CASE WHEN you have selected the OpensStreetMap baselayer

Map order:
   --------- Cached layers block, ordered 
   Layer C
   Layer E
   --------- single WMS layers block, ordered
   Layer A
   Layer B
   Layer D
   --------- Baselayer
   OpenStreetMap (or Bing or whatever)

CASE WHEN you have selected the Lizmap BaseLayer E as baselayer

Map order:
   --------- Cached layers block, ordered 
   Layer C
   Layer E
   --------- single WMS layers block, ordered
   Layer A
   Layer B
   Layer D
   BaseLayer E
  ---------------

The base layers are obviously always placed at the bottom, but for the other two block I had to choose (arbitrarily, I would say) which one goes on top . IMHO there is no general right solution for this problem, but maybe you have a some suggestions about that.

Funded by Faunalia

[mind84]

Test notes:

Waiting for Lizmap plugin "single layer" option development, you can switch from a mode to another by adding the attached js file as custom js in media folder.

switch_to_single_layer.js.zip

For now, I've only added a test project single_wms_image.qgs.

e2e
I think it's best to wait for a first review before writing tests

Known failure on e2e tests when single Layer mode is turned on:

• Tests related to opacity fails, since the opacity option is hidden and users can't act on it
• some tests when comparison between screenshots is
  required (due to the fact that the image is loaded into a separate map)

UPDATE

These test notes are now outdated since the singleWMS configuration is loaded from project config

[rldhont]

Before doing some reviews, we need to decide where and how to store in the config this new option.

@Gustry @mdouchin Do we add wmsSingleLayer or wmsSingleMapLayer in options ?

[mdouchin]

Before doing some reviews, we need to decide where and how to store in the config this new option.

@Gustry @mdouchin Do we add wmsSingleLayer or wmsSingleMapLayer in options ?

I would use wmsSingleRequestForAllLayers

Side idea: I think we should remove the active base layer (and obviously the externally requested WMS layers such as TMS) from the "single" image request. This would avoid having an empty map when zooming or panning (the base layer would come independently)

[mind84]

Side idea: I think we should remove the active base layer (and obviously the externally requested WMS layers such as TMS) from the "single" image request. This would avoid having an empty map when zooming or panning (the base layer would come independently)

@mdouchin ,
For now baseLayer(s) are excluded from the single request. At least that's what I tried to do :)

[mdouchin]

@mind84 What about the WMS layers when the user has checked the checkbox Get images directly from WMS Server ?

I would not put them in the "single layer" group of layers, but I have no strong opinion about it. Any hint @Gustry @rldhont ?

[mind84]

Hi @mdouchin!

What about the WMS layers when the user has checked the checkbox Get images directly from WMS Server ?

Right, I didn't consider that option.

In this case excluding it means that the layer will go on top.

[rldhont]

@mind84 What about the WMS layers when the user has checked the checkbox Get images directly from WMS Server ?

I would not put them in the "single layer" group of layers, but I have no strong opinion about it. Any hint @Gustry @rldhont ?

I think, if single layer is checked, then Get images directly from WMS Server is disabled.

[Gustry]

I think, if single layer is checked, then Get images directly from WMS Server is disabled.

This is not done for now on the plugin side.

[Gustry]

From the UX point of view

[Gustry]

I think, if single layer is checked, then Get images directly from WMS Server is disabled.

Can you make a ticket in plugin ?

@nboisteault Is this PR OK for you ?

[nboisteault]

@mind84 Many thanks for this work. There is just those messages in the console to look at please:

simplescreenrecorder-2024-03-19_14.17.10.mp4

[mind84]

@mind84 Many thanks for this work. There is just those messages in the console to look at please:

Yep, thanks, I'll fix it