cursor

NOTE: This version of the documentation tracks unstable development happening on A-Frame’s master branch. If you wish to try it out, grab the unstable build. Otherwise, head to the documentation for the current 1.6.0 version

The cursor component provides hover and click states for interaction on top of the raycaster component. The cursor component can be used for both gaze-based and controller-based interactions, but the appearance needs to be configured depending on the use case. The <a-cursor> primitive provides a default reticle appearance for a gaze-based cursor, and the laser-controls component configures the cursor for all controllers.

The cursor component listens to events and keeps state on what’s being hovered and pressed in order to provide mousedown, mouseup, mouseenter, mouseleave, and click events. We use the name mouse to mimic traditional web development for now. Under the hood, the cursor component uses the raycaster-intersection and raycaster-intersection-cleared events, capturing the closest visible intersected entity.

By default, the cursor is configured to be used in a gaze-based mode and will register user input via mouse or touch. Specifying the downEvents and upEvents properties allows the cursor to work with controllers. For example, the laser-controls component automatically configures these properties to work with most controllers.

To provide a shape or appearance to the cursor, we should apply either the geometry and material components or use the raycaster component’s showLine property to draw a line using the line component.

Example

For example, we can create a ring-shaped cursor fixed to the center of the screen. To fix the cursor to the screen so the cursor is always present no matter where we look, we place it as a child of the active camera entity. We pull it in front of the camera by placing it on the negative Z axis. When the cursor clicks on the box, we can listen to the click event.

<a-entity camera look-controls>
  <a-entity cursor="fuse: true; fuseTimeout: 500"
            position="0 0 -1"
            geometry="primitive: ring; radiusInner: 0.02; radiusOuter: 0.03"
            material="color: black; shader: flat">
  </a-entity>
</a-entity>

<a-entity id="box" cursor-listener geometry="primitive: box" material="color: blue"></a-entity>

// Component to change to a sequential color on click.
AFRAME.registerComponent('cursor-listener', {
  init: function () {
    var lastIndex = -1;
    var COLORS = ['red', 'green', 'blue'];
    this.el.addEventListener('click', function (evt) {
      lastIndex = (lastIndex + 1) % COLORS.length;
      this.setAttribute('material', 'color', COLORS[lastIndex]);
      console.log('I was clicked at: ', evt.detail.intersection.point);
    });
  }
});

Properties

Property	Description	Default Value
downEvents	Array of additional events on the entity to listen to for triggering `mousedown` (e.g., `triggerdown` for vive-controls).	[]
fuse	Whether cursor is fuse-based.	false on desktop, true on mobile
fuseTimeout	How long to wait (in milliseconds) before triggering a fuse-based click event.	1500
mouseCursorStylesEnabled	Whether to show pointer cursor in `rayOrigin: mouse` mode when hovering over entity.	true
rayOrigin	Where the intersection ray is cast from (i.e. xrselect ,entity or mouse). `rayOrigin: mouse` is extremely useful for VR development on a mouse and keyboard.	entity
upEvents	Array of additional events on the entity to listen to for triggering `mouseup`.	[]

To further customize the cursor component, we configure the cursor’s dependency component, the raycaster component.

Events

Event	Description
click	Emitted on both cursor and intersected entity if a currently intersected entity is clicked (whether by mouse or by fuse).
fusing	Emitted on both cursor and intersected entity when fuse-based cursor starts counting down.
mousedown	Emitted on both cursor and intersected entity (if any) on mousedown on the canvas element.
mouseenter	Emitted on both cursor and intersected entity (if any) when cursor intersects with an entity.
mouseleave	Emitted on both cursor and intersected entity (if any) when cursor no longer intersects with previously intersected entity.
mouseup	Emitted on both cursor and intersected entity (if any) on mouseup on the canvas element.

Event Data

Additional detail is included in the detail object on the event as follows:

intersection

Relevant events will contain in the event detail intersection, which will contain {distance, point, face, faceIndex, indices, object} about specific data about the intersection:

this.el.addEventListener('click', function (evt) {
  console.log(evt.detail.intersection.point);
});

intersectedEl

Events emitted on the cursor entity also include event detail intersectedEl, which provides a reference to the intersected entity.

mouseEvent and touchEvent

Where the trigger for a cursor event is a MouseEvent or TouchEvent, event detail mouseEvent or touchEvent provides a reference to that event.

These events provide a wealth of additional detail about the event, as detailed in the APIs linked above. Among other things, they can indicate:

which mouse button was used
information about the state of the mouse buttons (or multi-touch for touch events), and relevant keys shuch as Shift, Ctrl etc. at the time of the mouse or touch event.
the screen co-ordinates where the event occured.

This information can be used by applications to handle cursor events differently, depending on this information (e.g. different handling of left click & right click).

For example:

this.el.addEventListener('click', function (evt) {
  if (!evt.detail.mouseEvent || evt.detail.mouseEvent.button === 0) {
    console.log("left button clicked (or touch event / no information)");

  } else if (evt.detail.mouseEvent.button === 2) {
    console.log("right button clicked");
  }
});

At most one of mouseEvent or touchEvent will be present on a cursor event, and sometimes neither will. Neither will be present on mousenter, mouseleave and fusing events, nor on a click event that has been triggered by a fuse timeout rather than a mouse click or touch event.

States

The cursor will add states to the cursor entity on certain events:

State	Description
cursor-fusing	Added when the cursor is fusing on another entity.
cursor-hovering	Added when the cursor is hovering over another entity.

The cursor will add states to intersected entities on certain events:

State	Description
cursor-hovered	Added to the intersected entity when the cursor is hovering over it.

Configuring the Cursor through the Raycaster Component

The cursor builds on top of and depends on the raycaster component. If we want to customize the raycasting pieces of the cursor, we can do by changing the raycaster component properties. Say we want set a max distance, check for intersections less frequently, and set which objects are clickable:

<a-entity cursor raycaster="far: 20; interval: 1000; objects: .clickable"></a-entity>

Fuse-Based Cursor

Also known as gaze-based cursor. If we set the cursor to be fuse-based, the cursor will trigger a click if the user gazes at an entity for a set amount of time. Imagine a laser strapped to the user’s head, and the laser extends out into the scene. If the user stares at an entity long enough (i.e., the fuseTimeout), then the cursor will trigger a click.

The advantage of fuse-based interactions for VR is that it does not require extra input devices other than the headset. The fuse-based cursor is primarily intended for Google Cardboard applications. The disadvantage of fuse-based interactions is that it requires the user to turn their head a lot.

Adding Visual Feedback

To add visual feedback to the cursor to show when the cursor is clicking or fusing, we can use the animation component. When the cursor intersects the entity, it will emit an event, and the animation system will pick up event with the begin attribute:

<a-entity
  animation__click="property: scale; startEvents: click; easing: easeInCubic; dur: 150; from: 0.1 0.1 0.1; to: 1 1 1"
  animation__fusing="property: scale; startEvents: fusing; easing: easeInCubic; dur: 1500; from: 1 1 1; to: 0.1 0.1 0.1"
  animation__mouseleave="property: scale; startEvents: mouseleave; easing: easeInCubic; dur: 500; to: 1 1 1"
  cursor="fuse: true;"
  material="color: black; shader: flat"
  position="0 0 -3"
  geometry="primitive: ring"></a-entity>

To play with an example of a cursor with visual feedback, check out the Cursor with Visual Feedback example on CodePen.

XR Select Cursor

When an XR "selectstart" event happens the raycaster picks an element based upon it’s current location. This works for handheld AR, and headmounted VR and AR. This works well with the mouse rayOrigin too.

<a-scene
  cursor__mouse="rayOrigin: mouse"
  cursor__xrselect="rayOrigin: xrselect"
  raycaster="objects:#objects *;"
>