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    Function MapToViewportCoords

    • Maps a display-space pointer position on the live canvas to the server browser's VIEWPORT pixel space.

      The canvas's internal resolution (canvasWidth/canvasHeight, set from each pushed frame) IS the viewport pixel space; the canvas is displayed scaled to its bounding rect. So a display point maps as vx = (clientX - rect.left) / rect.width * canvasWidth (and likewise for y), rounded to ints. Returns null for a zero-size rect or un-sized canvas (divide-by-zero / not-ready guard).

      Pure + framework-free so it's unit-testable without a DOM.

      Parameters

      • clientX: number

        The pointer's viewport X in the DOM (event.clientX).

      • clientY: number

        The pointer's viewport Y in the DOM (event.clientY).

      • rect: { height: number; left: number; top: number; width: number }

        The canvas's bounding rect (getBoundingClientRect()).

      • canvasWidth: number

        The canvas's internal pixel width (= frame/viewport width).

      • canvasHeight: number

        The canvas's internal pixel height (= frame/viewport height).

      Returns { x: number; y: number } | null

      Integer viewport coordinates, or null when mapping isn't possible.

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