LastClick

Synesthesia hands your script.js the mouse position (_muvc) and the button states (_click), but not the thing you actually want for dragging: how far the mouse moved since the last frame. That’s a delta, and a delta needs memory.

LastClick is that memory — three lines, and it’s the foundation of every click-and-drag interaction in a scene.

function LastClick() { this.x = -100; this.y = -100; }

LastClick.prototype.click   = function () { this.x = _muvc.x; this.y = _muvc.y; };
LastClick.prototype.release = function () { this.x = -100; this.y = -100; };

The -100 matters more than it looks. It’s a sentinel meaning “not currently dragging”, parked far outside the coordinate range _muvc can ever return. Without it, the first frame of a drag would diff the current position against whatever was left over from the last drag — and the camera would snap by the full distance between them before settling.

So the rule is: always gate the diff on the sentinel.

Usage

var lastL = new LastClick();

function setup() {
    onOffToOn('_click', 'onDown');
    onOnToOff('_click', 'onUp');
}

function onDown() { lastL.click(); }
function onUp()   { lastL.release(); }

function update(dt) {
    var deltaX = 0, deltaY = 0;

    if (lastL.x > -50) {                    // -50, not -100: see notes
        deltaX = _muvc.x - lastL.x;
        deltaY = _muvc.y - lastL.y;
        lastL.click();                      // re-anchor for the next frame
    }

    cam_rd.smooth(cam_rd.goal_x + deltaX * 2.0,
                  cam_rd.goal_y + deltaY * 2.0,
                  cam_rd.goal_z);
}

Note the lastL.click() inside the drag branch — you re-anchor every frame, so the delta stays per-frame rather than accumulating from where the drag started.

Notes

• Test against -50, not -100. Comparing to the exact sentinel is fragile; any value below -50 is unreachable for a real cursor, so the loose threshold is both safer and self-documenting.
• _click is a vec3 — left, right, and middle button states. Track a separate LastClick per button if you want them to do different things (orbit on left, pan on middle, dolly on right is the usual mapping).
• Event callbacks are passed as string names, not function references: onOffToOn('_click', 'onDown'). Passing the function itself fails quietly.
• _muvc is the centered mouse UV. _muv is the 0–1 version — pick whichever matches the space you’re working in and don’t mix them.
• To get inertia for free, feed the delta into a Smooth3 goal rather than into the camera value directly, and multiply the delta by 0.95 each frame after release so the motion coasts to a stop.