Callback after the user taps the screen. Performs a hit test using Amazon Sumerian's ArSystem, which forwards the request to the device-native AR subsystem (ARCore / ARKit).

AnchorPositioning.js

// Touch handler.
// As the first step, performs a hit test at the currrent screen location.
performHitTest(evt) {
	// Check if this script is currently in an active place mode.
	// That is triggered when another component in the scene sent the
	// StartPlaceWorld event.
	if (!this.placeMode.get()) {
		// Currently not place mode - don't proceed!
		console.log("Not in place mode - not proceeding");
		return;
	}

	// Optional debug info
	console.log("Perform hit test: " + JSON.stringify(evt));

	// The pixel ratio and the viewport size is needed to convert from
	// the coordinates of the client area (the window) to the 3D scene coordinates.
	var pixelRatio = this.internalWorld.sumerianRunner.renderer.devicePixelRatio;

	// Get the touch coordinates and multiply them with the pixel ratio.
	// On a phone, you'd normally get the coordinates through changedTouches.
	// Especially for testing on a browser and also for improved compatibility,
	// we also check for mouse coordinates as well.
	var touchX;
	var touchY;
	if (evt.changedTouches) {
		// Touch screen
		touchX = evt.changedTouches[0].pageX * pixelRatio;
		touchY = evt.changedTouches[0].pageY * pixelRatio;
	} else {
		// Mouse
		touchX = evt.clientX * pixelRatio;
		touchY = evt.clientY * pixelRatio;
	}

	// Perform the coordinate normalization using the viewport width and height
	var normalizedX = touchX / this.internalWorld.sumerianRunner.renderer.viewportWidth;
	var normalizedY = touchY / this.internalWorld.sumerianRunner.renderer.viewportHeight;

	// Check again if the AR system is available
	if (this.arSystem) {
		console.log("AR System found: calling hit test callback...")
		// Perform hit test and then execute the hitTestCallback with the transform (position)
		// of the anchor that we will place.	
		this.arSystem.hitTest(normalizedX, normalizedY, (anchorTransform) => this.hitTestCallback(anchorTransform));
	}
}