[OpenLayers-Dev] Canvas + SelectFeature = Bug (OL 2.11/2.12)

[Mike Ryan]

Yep. But it will work as expected if you swap the order in 
SelectFeature. Of course, needing to do that is not expected.

Not that this might not be a nice feature to have. It could actually be 
very useful be able to click features underneath a layer.

-Mike

On 7/11/2012 3:00 PM, openlayers-dev-request at lists.osgeo.org wrote:
> True!
>
> But the original example also wrong using Canvas: using SVG can not select a
> markers if it is below a square, with Canvas you can, as if there were no
> rectangle!
>
> Xavier
>
>
> m1k3ry4n wrote
>> >
>> >When I render a layer as a Canvas it no longer respects the layer index.
>> >
>> >In my case, the Canvas layer is made up of polygons and a separate layer
>> >above it is made up of points. Any points within polygons cannot be
>> >selected -- only the surrounding polygon gets selected.
>> >
>> >I do not have this problem if the polygon layer is rendered as something
>> >other than a Canvas.
>> >
>> >This problem is caused by the order of the layers in the array sent to
>> >OpenLayers.Control.SelectFeature. The workaround is ordering the layers
>> >array so that the Canvas layer comes after layers that are above it in
>> >the layer index.
>> >
>> >In other words, even though I add layers to the map like this:
>> >map.addLayers([canvas_layer, point_layer])
>> >
>> >I have to add layers to the control like this:
>> >map.addControl(new OpenLayers.Control.SelectFeature([point_layer,
>> >canvas_layer]))
>> >
>> >To reproduce this problem do the following.
>> >
>> >1. Go to:
>> >http://openlayers.org/dev/examples/select-feature-multilayer.html?renderer=Canvas
>> >
>> >2. Swap the order of vectors1, vectors2 in lines 62 & 65 so they look
>> >like this:
>> >
>> >(line 62) map.addLayers([wmsLayer, vectors2, vectors1]);
>> >...
>> >(line 65) selectControl = new OpenLayers.Control.SelectFeature(
>> >                  [vectors2, vectors1],
>> >
>> >Changing addLayers puts the markers above the squares. Changing
>> >SelectFeature disallows markers within squares to be selected, even
>> >though they are above the squares. You will only see this problem if you
>> >render the layers as Canvases (i.e. include "?renderer=Canvas" in the
>> >url).
>> >
>> >Considering that layer order in SelectFeature has no effect on layers
>> >not rendered as Canvases, this is either a bug or requires some
>> >documentation for SelectFeature.
>> >
>> >This was also an issue in OL 2.11, but 2.12 improved the situation. In
>> >2.11 if you turned off the Canvas layer it persisted even though you
>> >could not see the layer! If you panned the map, it would finally go away
>> >and you could click the  layers below.
>> >
>> >-Mike
>> >
>> >
>> >Reference:
>> >OpenLayers.Control.SelectFeature
>> >http://dev.openlayers.org/docs/files/OpenLayers/Control/SelectFeature-js.html#OpenLayers.Control.SelectFeature.OpenLayers.Control.SelectFeature
>> >
>> >OpenLayers Select Feature on Multiple Layers Example
>> >http://openlayers.org/dev/examples/select-feature-multilayer.html?renderer=Canvas
>> >
>> >


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