Re: [Development] Copying QJSValue arrays
On Sunday 28. September 2014 15.17.34 Paul Lemire wrote:
Hi guys,
We're working on being able to set GLSL uniform arrays from QML.
Basically what we have is a QParameter QObject exposed to QML as Parameter.
It contains a QString name property and a QVariant value property.
Here's how it can be used for scalar types.
Parameter { name : uniformName; value : 1.0; }
What we want is to send a copy of value to our backend renderer, so that we
won't have any problem with threading. For scalar types, the copy is done
implicitly.
For array types, we'd like to be able to do something like that:
property var myArray : [1.0, 1.0, 1.0]
Parameter { name : uniformArray; value : myArray }
However in that case, value is a QJSValue containing a JS Array object.
We need a way to be able to copy that object.
The tricky part there is that we can't check the QVariant to to see if it
contains a QJSValue directly as we don't want to introduce a dependency to
the QML module.
We're thinking of maybe introducing a Qt.array helper function that would
return us a copy of the array directly or retrieve a QVectorQVariant.
If you've got ideas around that issue, please step in.
If you don't want to depend on QtQml (which seems odd for a library that offers
Qml bindings), then what you could do is utilize the conversion functions. So
after checking your QVariant for all other types you're interested in
supporting, you can try
canConvertQVariantList()
and afterwards convert to that. This will trigger a registered conversion
function that will convert the JavaScript array object, that the QJSValue
wraps, into a QVariant list that is not dependent on the JS engine anymore.
A QJSValue wrapped in a QVariant is (through QVariant) API always convertible
to a QVariantList and a QVariantMap - it's a shortcut to writing
qvariant_castQJSValue(variant).toVariant().valueTypeYouWant();
without using QJSValue. Due to the custom conversion functions being
unconditional you can however not distinguish between a regular JavaScript
object or an array. Therefore if the property contains an object the
conversion to an array will cause a loss of data.
If you don't want to loose any data, you're going to have to support the types
the QVariant can contain, and that includes direct support for QJSValue.
Simon
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Re: [Development] Copying QJSValue arrays
Hi Simon,
On Monday 29 Sep 2014 09:20:00 Simon Hausmann wrote:
On Sunday 28. September 2014 15.17.34 Paul Lemire wrote:
We're working on being able to set GLSL uniform arrays from QML.
Basically what we have is a QParameter QObject exposed to QML as
Parameter.
It contains a QString name property and a QVariant value property.
Here's how it can be used for scalar types.
Parameter { name : uniformName; value : 1.0; }
What we want is to send a copy of value to our backend renderer, so that
we
won't have any problem with threading. For scalar types, the copy is done
implicitly.
For array types, we'd like to be able to do something like that:
property var myArray : [1.0, 1.0, 1.0]
Parameter { name : uniformArray; value : myArray }
However in that case, value is a QJSValue containing a JS Array object.
We need a way to be able to copy that object.
The tricky part there is that we can't check the QVariant to to see if it
contains a QJSValue directly as we don't want to introduce a dependency to
the QML module.
We're thinking of maybe introducing a Qt.array helper function that would
return us a copy of the array directly or retrieve a QVectorQVariant.
If you've got ideas around that issue, please step in.
If you don't want to depend on QtQml (which seems odd for a library that
offers Qml bindings), then what you could do is utilize the conversion
functions.
Yeah it sounds odd. The reason is that we hope to offer both C++ and QML apis
for Qt3D where the plain C++ interface doesn't depend upon QtQml.
So after checking your QVariant for all other types you're
interested in supporting, you can try
canConvertQVariantList()
and afterwards convert to that. This will trigger a registered conversion
function that will convert the JavaScript array object, that the QJSValue
wraps, into a QVariant list that is not dependent on the JS engine anymore.
A QJSValue wrapped in a QVariant is (through QVariant) API always
convertible to a QVariantList and a QVariantMap - it's a shortcut to
writing
qvariant_castQJSValue(variant).toVariant().valueTypeYouWant();
without using QJSValue. Due to the custom conversion functions being
unconditional you can however not distinguish between a regular JavaScript
object or an array. Therefore if the property contains an object the
conversion to an array will cause a loss of data.
If you don't want to loose any data, you're going to have to support the
types the QVariant can contain, and that includes direct support for
QJSValue.
Right. We're also considering having the property setter function call a
helper virtual which in C++ lib does nothing but in the QML dependent lib
takes care of extracting and copying the data.
Thank you for your ideas.
Sean
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[Development] Copying QJSValue arrays
Hi guys,
We're working on being able to set GLSL uniform arrays from QML.
Basically what we have is a QParameter QObject exposed to QML as Parameter.
It contains a QString name property and a QVariant value property.
Here's how it can be used for scalar types.
Parameter { name : uniformName; value : 1.0; }
What we want is to send a copy of value to our backend renderer, so that we
won't have any problem with threading. For scalar types, the copy is done
implicitly.
For array types, we'd like to be able to do something like that:
property var myArray : [1.0, 1.0, 1.0]
Parameter { name : uniformArray; value : myArray }
However in that case, value is a QJSValue containing a JS Array object.
We need a way to be able to copy that object.
The tricky part there is that we can't check the QVariant to to see if it
contains a QJSValue directly as we don't want to introduce a dependency to the
QML module.
We're thinking of maybe introducing a Qt.array helper function that would
return us a copy of the array directly or retrieve a QVectorQVariant.
If you've got ideas around that issue, please step in.
Thanks,
Paul Lemire
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