fastblur | linear time ) implementation of the Gaussian Blur algorithm | Learning library

It's not perfect, but it works. Quick demo of how to do it:

main.qml

Things to be considered while using graphical effects. Effects have to be applied only to the required item or as a layer. In your case of DropShadow and Blur recursively applied since it's been used inside the item that intends to get effects.

Change the drop shadow & blur item's as below way. This resolves the issue. I have checked with QtQuick2.9 & Ubuntu OS

As I pointed out in the comments I do not get the warning message, also that the code is valid so I can presume that it is an old bug.

But also as the OP points out there is another problem: every time a search is made, new elements are added to the model and that is caused because every time it is filtered, the "project_proxy_list_model" qproperty must be obtained, therefore this function is invoked , and in the logic of the OP is that 4 new items are loaded, which is wrong, the logic is to return the model and not use another method.

I'm updating this answer as the question has been partially cleared in the comments, but I will leave the original answer at the end, as it might still be useful.

Besides that, the concept at the base remains the same: a graphics effect is applied to an object, and it modifies that object look, not how underlying objects appear. If you want to apply that effect to multiple objects, they have to be children of a common parent, and the effect has to be set for that parent, but everything that is below that parent (and it's not its child) will only be partially affected by the result of the effect.
Imagine a blur effect as a filter applied to a real life photograph that is partially transparent: while the image in the photograph is blurred, what you can see behind it will not be blurred.

QGraphicsEffects don't provide the ability to limit the extent of their processing, as they usually modify the whole "bounding rect" of the object they are set for.
In order to achieve that, subclassing is necessary and the draw() method has to be overridden, as it is the one responsible for the actual drawing.

I'm going to presume that the whole interface is going to be affected by the effect in some way: even if some objects are "outside" the rectangle of the effect, they are still part of the same parent, so this is what we're going to do:

• create a main widget that acts as container for the full interface
• add a main layout for the main interface (the one normally shown)
• create a sub widget that contains the main interface, set a layout for it and add anything you need to that layout
• set the subclassed graphics effect to the sub widget
• create a widget for the menu, that has the main widget as parent, so it will not be part of the main layout; it will have its own layout with its buttons, labels, etc.
• add a system that changes the graphics effect according to the geometry of the menu, and whenever that changes, the effect will be applied to that geometry only