General.Web/wwwroot/lib/codemirror-5.31.0/src/display/scroll_events.js

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import { chrome, gecko, ie, mac, presto, safari, webkit } from "../util/browser"
import { e_preventDefault } from "../util/event"

import { updateDisplaySimple } from "./update_display"
import { setScrollLeft, updateScrollTop } from "./scrolling"

// Since the delta values reported on mouse wheel events are
// unstandardized between browsers and even browser versions, and
// generally horribly unpredictable, this code starts by measuring
// the scroll effect that the first few mouse wheel events have,
// and, from that, detects the way it can convert deltas to pixel
// offsets afterwards.
//
// The reason we want to know the amount a wheel event will scroll
// is that it gives us a chance to update the display before the
// actual scrolling happens, reducing flickering.

let wheelSamples = 0, wheelPixelsPerUnit = null
// Fill in a browser-detected starting value on browsers where we
// know one. These don't have to be accurate -- the result of them
// being wrong would just be a slight flicker on the first wheel
// scroll (if it is large enough).
if (ie) wheelPixelsPerUnit = -.53
else if (gecko) wheelPixelsPerUnit = 15
else if (chrome) wheelPixelsPerUnit = -.7
else if (safari) wheelPixelsPerUnit = -1/3

function wheelEventDelta(e) {
  let dx = e.wheelDeltaX, dy = e.wheelDeltaY
  if (dx == null && e.detail && e.axis == e.HORIZONTAL_AXIS) dx = e.detail
  if (dy == null && e.detail && e.axis == e.VERTICAL_AXIS) dy = e.detail
  else if (dy == null) dy = e.wheelDelta
  return {x: dx, y: dy}
}
export function wheelEventPixels(e) {
  let delta = wheelEventDelta(e)
  delta.x *= wheelPixelsPerUnit
  delta.y *= wheelPixelsPerUnit
  return delta
}

export function onScrollWheel(cm, e) {
  let delta = wheelEventDelta(e), dx = delta.x, dy = delta.y

  let display = cm.display, scroll = display.scroller
  // Quit if there's nothing to scroll here
  let canScrollX = scroll.scrollWidth > scroll.clientWidth
  let canScrollY = scroll.scrollHeight > scroll.clientHeight
  if (!(dx && canScrollX || dy && canScrollY)) return

  // Webkit browsers on OS X abort momentum scrolls when the target
  // of the scroll event is removed from the scrollable element.
  // This hack (see related code in patchDisplay) makes sure the
  // element is kept around.
  if (dy && mac && webkit) {
    outer: for (let cur = e.target, view = display.view; cur != scroll; cur = cur.parentNode) {
      for (let i = 0; i < view.length; i++) {
        if (view[i].node == cur) {
          cm.display.currentWheelTarget = cur
          break outer