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.christop...@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:
>
>
> 1. Create a neighbour Effect element (ColorOverlay here)
> 2. Set orginal item as the effect source
> 3. Set the effect size (fill original item)
> 4. Specificy effect specific properties (color here)
> 5. 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:
>
>
>
>
> 1. Set an Effect element (ColorOverlay here) as a value for the item
> layer property
> 2. Enable the layering with (layer.enabled : true) => I wonder why it
> defaults at "false"
> 3. 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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