[Interest] QtGraphicalEffects usage questioning

[Mark Gaiser]

Same here.
The current way is vague and requires a lot of trial and error.
It works, yes! But a more intuitive way to apply effect would
certainly be welcome.

On Wed, Apr 2, 2014 at 8:05 PM, Julien Cugnière
<julien.cugniere at gmail.com> wrote:
> Hi,
>
> I just wanted to mention that I've had the exact same problems as you when
> trying to use the graphical effects, so you're not alone ! They're powerful,
> but the documented way to use them is cumbersome, and not quite what you
> would expect.
>
> By the way, thanks for the layer trick, it's definitely an improvement, and
> I'm not sure I'd have ever stumbled upon it by myself ! It really should be
> advertised more in the documentation.
>
>
> Julien Cugnière
>
>
> 2014-04-02 18:38 GMT+02:00 Christopher Courtois
> <courtois.christopher at gmail.com>:
>>
>> I've recently started to use QtGraphicalEffects module and the effect set
>> is really nice!
>>
>> Howerver I think the approach to apply an effect on a qml item is somewhat
>> cumbersome.
>>
>>
>>
>> The docs give an example where we need to create an effect as a neighbour
>> of the original item :
>>
>>
>>
>> Item {
>>
>>     width: 300
>>
>>     height: 300
>>
>>
>>
>>     Image {
>>
>>         id: bug
>>
>>         source: "images/butterfly.png"
>>
>>         sourceSize: Qt.size(parent.width, parent.height)
>>
>>         smooth: true
>>
>>         visible: false
>>
>>     }
>>
>>
>>
>>     ColorOverlay {
>>
>>         anchors.fill: bug
>>
>>         source: bug
>>
>>         color: "#80800000"
>>
>>     }
>>
>> }
>>
>>
>>
>> In this case 5 steps are needed to apply an effect:
>>
>>  Create a neighbour Effect element (ColorOverlay here)
>>  Set orginal item as the effect source
>>  Set the effect size (fill original item)
>>  Specificy effect specific properties (color here)
>>  Hide the original item
>>
>>
>>
>> It actually feels cumbersome and not really natural for me to apply an
>> effect this way.
>>
>> But worse than that it breaks two things : hierarchy and visibility logic.
>>
>> Indeed if you want to apply effects on existing qml code you will need to
>> rewrite you code because this implies hierarchy changes.
>>
>> If you unfortunately use positioners or layouts elements it is a REAL PAIN
>> since you need to create wrappers for the original item and effect otherwise
>> you will have "holes" in your layout since those are 2 separates items.
>>
>> Lastly if you have some logic that takes care of your original item
>> visibly, the use of effect will sadly bypass it since it renders even
>> invisible items.
>>
>>
>>
>> For all those reasons I would really appreciate a better API to apply
>> effect on on existing code without messing with hiearchy and logic.
>>
>> I then looked in the QtQuick Item API and found the "layer" attribute
>> which seems to fill this purpose.
>>
>>
>>
>> So here the same effect example using the layer property :
>>
>>
>>
>> Item {
>>
>>     width: 300
>>
>>     height: 300
>>
>>
>>
>>     Image {
>>
>>         id: bug
>>
>>         source: "images/butterfly.png"
>>
>>         sourceSize: Qt.size(parent.width, parent.height)
>>
>>         smooth: true
>>
>>         layer {
>>
>>                 enabled: true
>>
>>                 effect:   ColorOverlay {
>>
>>            color: "#80800000"
>>
>>      }
>>
>>        }
>>
>>     }
>>
>>  }
>>
>>
>>
>> Here are the needed steps  with this approach:
>>
>>
>>
>>  Set an Effect element (ColorOverlay here) as a value for the item layer
>> property
>>  Enable the layering with (layer.enabled : true)   => I wonder why it
>> defaults at "false"
>>  Specificy effect specific properties (color here)
>>
>>
>>
>> I think this second approach is way more clean/simple and compatible with
>> existing code than the first one so I'm wondering why this is not the
>> "recommended" way to use effects in documentation.
>>
>>
>>
>> I'm not saying that the first approach is useless since in some cases you
>> will need to have both the original item and the effect (e.g. mirror effect)
>> displayed,
>>
>> But in most case for the effects in QtGraphicalEffects the effect is meant
>> to replace the original item so the documented approach would better figured
>> as an alternative way to do effects.
>>
>>
>>
>> This second approach still have some issues:
>>
>>
>>  The type of layer property is actually "Component" not "Item" so that's
>> mean you can't create alias on your effect properties
>> ð I 'm still wondering why the type is Component by the way
>> Even is the code doesn't mean it, the engine seems to changes the
>> hierarchy to render the effect => it creates a neighbour item effect under
>> the hood
>> ð  I created a bug report about this :
>> https://bugreports.qt-project.org/browse/QTBUG-37574
>>
>>
>> What do you think about this ?
>>
>> Regards,
>>
>> Christopher
>>
>>
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>
>
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