Function applyNextRange

src/interaction/createZoomState.ts:139–208

(
    nextStart: number,
    nextEnd: number,
    options?: { readonly emit?: boolean; readonly anchor?: { readonly center: number; readonly ratio: number } },
  )

  };

  const applyNextRange = (
    nextStart: number,
    nextEnd: number,
    options?: { readonly emit?: boolean; readonly anchor?: { readonly center: number; readonly ratio: number } },
  ): void => {
    if (!Number.isFinite(nextStart) || !Number.isFinite(nextEnd)) return;

    let s = nextStart;
    let e = nextEnd;

    if (s > e) {
      const t = s;
      s = e;
      e = t;
    }

    // Enforce span constraints by resizing around the proposed midpoint.
    let span = e - s;
    if (!Number.isFinite(span) || span < 0) return;

    const targetSpan = clamp(span, normalizedMinSpan, normalizedMaxSpan);
    if (targetSpan !== span) {
      const anchorCenter =
        options?.anchor && Number.isFinite(options.anchor.center)
          ? clamp(options.anchor.center, 0, 100)
          : (s + e) * 0.5;
      const anchorRatio =
        options?.anchor && Number.isFinite(options.anchor.ratio)
          ? clamp01(options.anchor.ratio)
          : 0.5;

      // Resize around the anchor so zoom operations preserve the cursor location.
      s = anchorCenter - anchorRatio * targetSpan;
      e = s + targetSpan;
      span = targetSpan;
    }

    // If span exceeds bounds (shouldn't happen with normalizedMaxSpan <= 100), clamp to full extent.
    if (span > 100) {
      s = 0;
      e = 100;
      span = 100;
    }

    // Shift into bounds without changing span.
    if (s < 0) {
      const shift = -s;
      s += shift;
      e += shift;
    }
    if (e > 100) {
      const shift = e - 100;
      s -= shift;
      e -= shift;
    }

    // Final clamp for tiny floating point drift.
    s = clamp(s, 0, 100);