Using the Pinch Manipulator¶

Use the Pinch Manipulator to enable users to zoom and rotate nodes in your Kanzi application.

For example, you can use the Pinch Manipulator to enable users to zoom into and out of a map. See Enabling the pinch gesture for a node.

Use the Pinch Manipulator triggers to react to the pinch gesture. For example, you can set the appearance of a node when the user zooms and rotates the node using the pinch gesture.

See Using the Pinch Manipulator triggers.

The Pinch Manipulator is one of the input manipulators you can use to add gesture recognition to nodes in your Kanzi application. See Using input manipulators.

Learn how to use the Pinch Manipulator by completing a tutorial. See Tutorial: Pan, zoom, tap.

Enabling the pinch gesture for a node¶

To enable the pinch gesture for a node:

In Kanzi Studio create a project using the Application template.
In the Node Tree create a node for which you want to enable the pinch gesture. For example, create an Image node and name it PinchNode.
In the Node Tree select the node that you created in the previous step, in the Properties add the Input > Hit Testable property, and set it to enabled.

When you enable this property you enable the user to pick a node.

By default hit testing is enabled for the Button, List Box Item Container, Scroll View, Slider, and Text Box nodes.

See Defining which node receives input.
In the Node Tree press Alt and right-click the node that you created and select Alias.

Kanzi Studio creates an alias pointing to the node from which you created the alias and adds it to the resource dictionary of its nearest ancestor node that contains a resource dictionary.

Access alias target nodes using the # sign followed by the name of the alias.
Select File > Export > Export KZB.

Kanzi Studio creates the kzb file and configuration files from your Kanzi Studio project. Kanzi Studio stores the exported files in the <ProjectName>/Application/bin directory or the location you set in Project > Properties in the Binary Export Directory property. The kzb file contains all nodes and resources from your Kanzi Studio project, except the resources you mark in a localization table as locale packs.

When you run your Kanzi application from Visual Studio, your application loads the kzb file and configuration files.
Open the command line in the <ProjectName>/Application directory and run
```
generate_cmake_vs2017_solution.bat
```
This script generates a Visual Studio solution for the application in the directory <ProjectName>/Application/build_vs2017.

Tip

You can open the project directory from Kanzi Studio by selecting File > Open in Windows Explorer.

In Visual Studio open the <ProjectName>/Application/build_vs2017/<ProjectName>.sln Visual Studio solution and in the file that implements the logic of your application create and configure the PinchManipulator:

Define the handlers for the pinch messages.

For example, after the public section of the class which implements the logic of your application add:

private:

    // Define the handler for the PinchManipulator::StartedMessage message from the 2D nodes
    // that have an input manipulator which generates pinch messages.
    // This handler prepares a 2D node for a pinch gesture.
    void onPinchStarted(PinchManipulator::StartedMessageArguments& messageArguments)
    {
        // Get from the message arguments the node that the user pinches.
        Node2DSharedPtr node2d = dynamic_pointer_cast<Node2D>(messageArguments.getSource());

        if (!node2d)
        {
            return;
        }

        // When starting a pinch gesture on the node, bring the node to front.
        node2d->moveToFront();

        // Store the initial value of the Render Transformation scale.
        SRTValue2D nodeTransform = node2d->getRenderTransformation();
        m_pinchInitialScaleFactor = nodeTransform.getScale().getX() - 1.0f;
    }

    // Define the handler for the PinchManipulator::MovedMessage message from the 2D nodes
    // that have an input manipulator which generates pinch messages.
    // This scales and rotates a 2D node for the amount of the pinch gesture.
    void onPinchMoved(PinchManipulator::MovedMessageArguments& messageArguments)
        {
        // Get from the message arguments the node that the user pinches.
        Node2DSharedPtr node2d = dynamic_pointer_cast<Node2D>(messageArguments.getSource());

        if (!node2d)
        {
            return;
        }

        float scale;

        // Get the scale and rotation from the message arguments.
        float scaleDelta = messageArguments.getScale();
        float rotateDelta = messageArguments.getRotation();

        // Get the Render Transformation property of the node.
        SRTValue2D nodeTransform = node2d->getRenderTransformation();

        // Calculate the scale by adding the initial scale to the pinch value.
        scale = scaleDelta + m_pinchInitialScaleFactor;

        // Apply the rotation.
        nodeTransform.rotate(rotateDelta);

        // Apply the scale.
        nodeTransform.setScale(Vector2(scale, scale));

        // To make the node rotate around its center instead of its upper left corner,
        // set the Render Transformation Origin property to (0.5, 0.5).
        node2d->setRenderTransformationOrigin(Vector2(0.5f, 0.5f));

        // Apply the new transform to the node.
        node2d->setRenderTransformation(nodeTransform);
    }

    // Initial scale factor for the pinch gesture.
    float m_pinchInitialScaleFactor;

In the public section of the class which implements the logic of your application, add the constructor and set the initial scale factor for the pinch gesture:
```
MyProject() :
    m_pinchInitialScaleFactor(0.0f)
{
}
```

In the onProjectLoaded() function create a PinchManipulator manipulator and subscribe to its messages.

For example, add:

 void onProjectLoaded() override
 {
     ScreenSharedPtr screen = getScreen();
     Domain* domain = getDomain();

     // Get the PinchNode node using its alias.
     NodeSharedPtr pinchNode = screen->lookupNode<Node>("#PinchNode");

     // Create an input manipulator that generates pinch messages.
     PinchManipulatorSharedPtr pinchManipulator = PinchManipulator::create(domain);

     // Add the input manipulator to the PinchNode.
     pinchNode->addInputManipulator(pinchManipulator);

     // Subscribe to the PinchManipulator::StartedMessage message at the PinchNode.
     // The PinchManipulator generates this message when the user presses two fingers on the attached node.
     pinchNode->addMessageHandler(PinchManipulator::StartedMessage, bind(&MyProject::onPinchStarted, this, placeholders::_1));

     // Subscribe to the PinchManipulator::MovedMessage message at the PinchNode.
     // The PinchManipulator generates this message first when the scale or rotation threshold is exceeded
     // and after that when the tracked touches have moved between updates.
     pinchNode->addMessageHandler(PinchManipulator::MovedMessage, bind(&MyProject::onPinchMoved, this, placeholders::_1));
}

Build and run your application. See Deploying Kanzi applications.

In the application zoom and rotate the node for which you enabled the pinch gesture.