| 27 | }; |
| 28 | |
| 29 | const normalizeWheelDeltaX = (e: WheelEvent, basisCssPx: number): number => { |
| 30 | const raw = e.deltaX; |
| 31 | if (!Number.isFinite(raw) || raw === 0) return 0; |
| 32 | |
| 33 | // Normalize to CSS pixels-ish so sensitivity is stable across deltaMode. |
| 34 | switch (e.deltaMode) { |
| 35 | case WheelEvent.DOM_DELTA_PIXEL: |
| 36 | return raw; |
| 37 | case WheelEvent.DOM_DELTA_LINE: |
| 38 | return raw * 16; |
| 39 | case WheelEvent.DOM_DELTA_PAGE: |
| 40 | return raw * (Number.isFinite(basisCssPx) && basisCssPx > 0 ? basisCssPx : 800); |
| 41 | default: |
| 42 | return raw; |
| 43 | } |
| 44 | }; |
| 45 | |
| 46 | const wheelDeltaToZoomFactor = (deltaCssPx: number): number => { |
| 47 | // Positive delta = scroll down = zoom out; negative = zoom in. |