Layer effects in QGis

Since QGis version 2.10 you have at your disposal a
powerful tool to format the vector layers symbols.

The layer effects provide
the ability to add different effects in the rendering chain
of a symbol. With these effects , you can place a
shadow range under the
symbol, modifying and highlighting the rendering symbol. You can also use these effects overlapped and indicate if
the effect will be gradual, ie if it applies in  the rendering
state (it modifies the rendering already
modified by others effects ) or discreet , by re-entering the
geometric source in the rendering chain (
modifying the original symbol without taking into
account other effects and by adding them to
these ).

Let’s discuss a few
examples that will clarify all the previous. Firstly ,
where is this option located?

Open
Layer Properties-> Style

Check
the Effects box to activate the effects on this layer and click the Effects button to open the
Effect Settings window.  

Out of the 5 available effects types, you have by default the effect
Source. In
fact it is a non- effect
because this option displays the original symbol of the layer . On the other
side, if you apply
, for example , a given shadow and you uncheck Source , on your map, you will see only the
shadows of the entities of this layer but not the entities themselves
.

The effects are
drawn the following
order of this window ,
the one placed the lowest is drawn first whereas the one placed
the highest, the last .

The
arrows allow moving an effect up or
down.

With
the + button , you can add other effects to the  5 by default effects.

Let’s discuss how these effects
are translated in a data layer. We will use a cadastre layer as example .

Let’s
apply a given shadow to the buildings:

You will observe that
the right panel allows setting up all the
parameters of the selected effect.

The
effect is conveyed as follows:

To
increase the separation effect between the buildings and the plots, we will add an external luminescence zone .   

This effect will be applied after the shadow generation :

You can control the way the effects are applied in the
effects chain, with the option Drawing
Mode

The rendering mode only
applies the effect to the original symbol, not to the rendering status when
applying the effect . In our case the external Luminescence will be applied, just, to the original polygon and not to the selected shadow .

The Edit option does
not have any effect at the top of the pile since
it modifies the rendering without displaying it
. It is used to change the status of the
rendering that will be passed to the effects being above it in the effects
stack.

The default mode, Rendering and Edit is the
combination of both: it applies the effect, draws and passes to the effects
located above the stack.

We cannot see here
all the possible effects combinations and their
renderings, but try ,
you will be surprised
with all you can do to make more striking the
renderings of your maps.

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