/**
* 2D affine transform stored as {x, y, scale}. Rotation is omitted
* for now — the lightbox uses axis-aligned pan + uniform zoom.
*/
export interface Transform2D {
	x: number;
	y: number;
	scale: number;
}
export declare const IDENTITY: Transform2D;
/**
* Apply a scale delta `k` around a point `(px, py)`, preserving the
* visual position of that point. This is the pinch-centroid math
* used by PhotoSwipe, Google Maps, and every serious image viewer.
*
* Derivation: let the current transform map (u, v) → (u*scale+x, v*scale+y).
* After scaling by `k` around (px, py) we want the pixel at (px, py)
* to remain at (px, py). Solving the system yields:
*
*     newScale = scale * k
*     newX     = px - (px - x) * k
*     newY     = py - (py - y) * k
*/
export declare function scaleAround(t: Transform2D, k: number, px: number, py: number): Transform2D;
/** Clamp scale to `[min, max]` without moving the origin. */
export declare function clampScale(t: Transform2D, min: number, max: number): Transform2D;
/** Translate by a pixel delta. */
export declare function translate(t: Transform2D, dx: number, dy: number): Transform2D;
/** Format as a CSS `transform` value using `translate3d` + `scale` for GPU compositing. */
export declare function toCss(t: Transform2D): string;
/** Midpoint between two 2D points. */
export declare function midpoint(a: {
	x: number;
	y: number;
}, b: {
	x: number;
	y: number;
}): {
	x: number;
	y: number;
};
/** Euclidean distance between two 2D points. */
export declare function distance(a: {
	x: number;
	y: number;
}, b: {
	x: number;
	y: number;
}): number;