Following the Mouse

A window's own events (mousemove, click…) come only while the pointer is over it. DesktopEngine.input follows the mouse anywhere on screen, over other apps too, e.g. for a companion whose eyes follow the pointer. It needs the mouse permission in the manifest and "apiVersion": 3:

"apiVersion": 3,
"permissions": ["mouse"]

const input = DesktopEngine.input;

input.onmousemove = ({ x, y }) => lookAt(x, y);
input.onmousedown = ({ x, y, button }) => blink(); // button: 0 primary, 1 middle, 2 secondary
input.onmouseup = () => {};
input.onwheel = ({ deltaX, deltaY }) => spin(deltaY);

// where the pointer is now, without waiting for it to move
const start = input.pointer; // { x, y }, null without the permission

Points are global, like DesktopEngine.Window and Screen: the origin is the top-left of the main display and y points down. Subtract a window's position to get a point in it.

• The events only watch: the pointer still goes to whatever is under it, and nothing is taken away from other apps.
• Moves and wheel turns that come faster than the content takes them are merged: the latest position, the sum of the deltas. Don't count events to measure distance, use the positions.
• The app watches the mouse only while the content listens to one of these events. Remove the listeners (input.onmousemove = null, removeEventListener, destroy()) when you no longer need them.
• Without the permission (not declared, or the user denied it) pointer is null and the events never come: plan for a companion that doesn't follow the pointer.
• Check DesktopEngine.apiVersion >= 3 before using DesktopEngine.input if the package also runs in apps with an older API.

On the web

In desktopengine dev --web and the store's previews, the mouse events come while the pointer is over the desktop on the page, also where the page's windows cover it.