Qt / QML:发送QImage从C ++到QML和显示QImage在GUI [英] Qt/QML : Send QImage From C++ to QML and Display The QImage On GUI
问题描述
我创建了一个类 Publisher
,它定期发出一个 QImage
对象。
然而,我有一个艰难的时候绘制 QImage
到一个QML元素。看起来 Image
和 Canvas
QML组件需要一个 QUrl
而不是 QImage
,但我不知道如何将我的 QImage
转换为 QUrl
。编辑4:当我说QUrl,我不意味着我试图将图像转换为URL。这是废话。我的意思是我想生成一个引用这个图像,这不是在磁盘上,并且QML组件要求的数据类型是一个URL。
做了一些研究,发现 QQuickImageProvider
提供了一个解决方案,但我还没有找到任何文档解释如何转换我的 QImage
信号到可以用于绘图的 QUrl
。
感谢您的帮助!
>我看了一下: http: //qt-project.org/doc/qt-5.0/qtquick/qquickimageprovider.html ,我没有看到我如何传递QImage到快速图像提供程序,并从它创建一个QUrl。
Edit2。这里是标题。实施不应该很重要。
class Publisher
{
Q_OBJECT
$ b b public:
Publisher(QObject * parent = 0);
virtual〜Publisher(void);
Q_SIGNALS:
void newImage(const QImage& newImage);
};
编辑3.这是我的QML代码,但我不知道如何绘制我的QImage,所以这段代码是没有意义的。
我的main.cpp文件:
int main(int argc,char * argv [])
{
QGuiApplication app(argc,argv);
qmlRegisterType< Publisher>(Components,1,0,Publisher);
QtQuick2ApplicationViewer viewer;
viewer.setMainQmlFile(QStringLiteral(qml / QQuickViewExample / main.qml));
view.showExpanded();
return app.exec();
}
my main.qml file :
import QtQuick 2.0
import Components 1.0
Rectangle {
id:testRect
width:360
height:360
图片{
anchors.fill:parent
id:myImage
Publisher {
id:myPub
onNewImage:{
myImage.source = newImage; #我知道这不工作,它需要一个QUrl而不是一个QImage
}
}
}
}
换句话说,你有一个类发出一个信号携带一个QImage,并想更新一个项目在QML与该图像?有各种解决方案,没有一个涉及将QImage转换为QUrl(无论什么意思,肯定你不需要得到一个数据
携带您的图像数据...)
使用图片提供程序
这意味着您可以使用一个简单的 Image
项目。
- 创建
QQuickImageProvider
子类;给它一个QImage
成员(图像到提供者),重写requestImage
提供该图像(实际id
请求并不重要,见下文)和一个接收QImage
并更新成员的槽。 - 将
发布者
信号连接到您的提供者插槽 - 通过<$ c将提供者安装到QML引擎$ c> QQmlEngine :: addImageProvider (见
QQuickView :: engine
);id 并不重要,只需使用一个明智的
-
在QML中,只需使用一个简单的
Image
具有此类源的元素图像{
id:myImage
source:image:// providerIdPassedToAddImageProvider / foobar
}
- 子类
QQuickPaintedItem
:子类存储QImage
被绘制,并有一个槽,设置新的QImage。它的paint
实现只是使用QPainter :: drawImage
来绘制图像。 - 通过
qmlRegisterType
(以便您可以在QML中使用它)将子类暴露给QML世界。 -
以将携带新图像的信号连接到项目的插槽。
这可能是棘手的部分。
要在C ++中执行连接,该项目已被创建(并获得一个指针);通常通过将
objectName
属性赋值为某个值,然后在根对象上使用findChild
由QQuickView :: rootObject()
返回,以获取该项本身的指针。然后,您可以照常使用connect
。
在QML中,就像上面一样,通过暴露给QML世界的发布者C ++对象上的
Connections
元素:MyItem {
id:myItem
}
Connections {
target:thePublisherObjectExposedFromC ++
onNewImage:myItem.setImage image)
}
这具有无论何时创建MyItem实例;但我不是100%肯定它会工作,因为我不确定你可以处理
QImage
类型在QML。 - Create a
QQuickImageProvider
subclass; give it aQImage
member (the image to provider), overriderequestImage
to provide that image (the actualid
requested does not really matter, see below), and a slot that receives aQImage
and updates the member. - Connect your
Publisher
signal to your provider's slot - Install the provider into the QML engine via
QQmlEngine::addImageProvider
(seeQQuickView::engine
); again theid
does not really matter, just use a sensible one In QML, just use a plain
Image
element with a source like thisImage { id: myImage source: "image://providerIdPassedToAddImageProvider/foobar" }
foobar
will be passed to your provider, but again, it doesn't really matter.We're almost there, we now only need a way to push the image updates to the QML world (otherwise Image will never know when to update itself). See my answer here for how to do that with a
Connections
element and a bit of JS.Note that in general you don't need to make
Publisher
a QML type, you just need to create one instance in C++ and expose it to the QML world viaQQmlContext::setContextProperty
.- Subclass
QQuickPaintedItem
: the subclass stores theQImage
to be painted and has a slot that sets the new QImage. Also itspaint
implementation simply paints the image usingQPainter::drawImage
. - Expose the subclass to the QML world via
qmlRegisterType
(so that you can use it in QML) Figure out a way to connect the signal carrying the new image to the items' slot.
This might be the tricky part.
To perform the connection in C++ you need a way to figure out that the item has been created (and get a pointer to it); usually one does this by means of assigning the
objectName
property to some value, then usingfindChild
on the root object (as returned byQQuickView::rootObject()
) to get a pointer to the item itself. Then you can useconnect
as usual.Or, could instead perform the connection in QML, just like above, via a
Connections
element on the publisher C++ object exposed to the QML world:MyItem { id: myItem } Connections { target: thePublisherObjectExposedFromC++ onNewImage: myItem.setImage(image) }
This has the advantage of working no matter when you create the MyItem instance; but I'm not 100% sure it will work because I'm not sure you can handle the
QImage
type in QML.
我们将会向您的供应商传递code> foobar 我们现在只需要一种方法来推动图像更新到QML世界(否则Image永远不会知道什么时候更新自己)。请参阅我的回答,了解如何使用连接
元素和一点JS。
请注意,一般来说,您不需要使 Publisher
一个QML类型,您只需要创建
ol>
使用自订的Qt Quick 2项目
QQuickPaintedItem
可能是最方便的工作,因为它提供了一个 paint
方法取一个 QPainter
。因此,大计划是
I created a class Publisher
which periodically emits a QImage
object.
However I'm having a tough time drawing the QImage
to a QML element. It appears that the Image
and Canvas
QML components require a QUrl
instead of a QImage
, but I'm not sure how to convert my QImage
to a QUrl
. Edit4: When I say QUrl, I don't mean I'm trying to convert an image to a URL. That's nonsense. I mean I want to generate a reference to this image, which is not on disk, and the data type that QML components are asking for is a URL.
I've done some research and found that QQuickImageProvider
provides a solution, but I haven't found any documentation explaining how to convert my QImage
signal to a QUrl
that I can use for drawing. Any example code or reference documentation would be appreciated.
Thanks for your help!
Edit1:
I've taken a look here: http://qt-project.org/doc/qt-5.0/qtquick/qquickimageprovider.html and I do not see how I pass a QImage to the quick image provider and from it create a QUrl.
Edit2. Here is the header. The implementation should not be important.
class Publisher
{
Q_OBJECT
public:
Publisher(QObject* parent = 0);
virtual ~Publisher(void);
Q_SIGNALS:
void newImage(const QImage& newImage);
};
Edit 3. Here is my QML code, but I don't know how to draw my QImage, so this code is kind of meaningless.
my main.cpp file:
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
qmlRegisterType<Publisher>("Components", 1, 0, "Publisher");
QtQuick2ApplicationViewer viewer;
viewer.setMainQmlFile(QStringLiteral("qml/QQuickViewExample/main.qml"));
viewer.showExpanded();
return app.exec();
}
my main.qml file:
import QtQuick 2.0
import Components 1.0
Rectangle {
id : testRect
width: 360
height: 360
Image{
anchors.fill: parent
id: myImage
Publisher {
id: myPub
onNewImage: {
myImage.source = newImage; #I know this doesnt work, it needs a QUrl and not a QImage
}
}
}
}
In other words, you have a class emitting a signal carrying a QImage and want to update an item in QML with that image? There are various solutions, none of which involves "converting a QImage to a QUrl" (whatever that means, surely you don't need to get a data
URL carrying your image data...)
Use an image provider
This means you can use a plain Image
item in your QML files.
Use a custom Qt Quick 2 Item
QQuickPaintedItem
is probably the most convenient for the job as it offers a paint
method taking a QPainter
. Hence the big plan is
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