ui/mouse.js: add event_movement() and wheel_delta() to fix event coords

Cross browser normalization of movementX,movementY and deltaX,deltaY is a hot mess, see:

https://bugs.chromium.org/p/chromium/issues/detail?id=1092358
https://bugzilla.mozilla.org/show_bug.cgi?id=1392460
w3c/uievents#181
w3c/pointerlock#42
mdn/content#11811

Signed-off-by: Tim Janik <[email protected]>

ui/mouse.js

@@ -0,0 +1,103 @@
+// This Source Code Form is licensed MPL-2.0: http://mozilla.org/MPL/2.0
+
+if (0) { // debug code
+  document.body.addEventListener ('wheel',       e => console.log (wheel_delta (e, true)), { capture: true, passive: true });
+  document.body.addEventListener ('pointermove', e => console.log (chrome_dppx + ':', e.clientX - last_event.clientX, event_movement (e, true)), { capture: true, passive: true });
+}
+
+/// Flag indicating Chrome UserAgent.
+// Indicates need for Chrome coordinate fixing.
+// See: https://bugs.chromium.org/p/chromium/issues/detail?id=1092358 https://github.com/w3c/pointerlock/issues/42
+export const CHROME_UA = (() => {
+  const chrome_match = /\bChrome\/([0-9]+)\./.exec (navigator.userAgent);
+  if (chrome_match) {
+    const chrome_major = parseInt (chrome_match[1]);
+    return chrome_major >= 37; // introduction of movementX, movementY
+  }
+  return false;
+}) ();
+
+// Measure dots-per-physical-pixel as Chrome workaround
+function body_move_event_4chrome (ev)
+{
+  const prev = last_event;
+  const ret = body_move_event (ev);
+  if (prev && prev != last_event &&
+      prev.screenY != last_event.screenY) {
+    const cy = last_event.clientY - prev.clientY;
+    const sy = last_event.screenY - prev.screenY;
+    chrome_dppx = Math.min (Math.max (cy * devicePixelRatio / sy, 1), 4);
+    // Done, swap-in the real handler
+    document.body.removeEventListener ("pointermove", body_move_event_4chrome, { capture: true, passive: true });
+    document.body.addEventListener ("pointermove", body_move_event, { capture: true, passive: true });
+  }
+  return ret;
+}
+let chrome_dppx = 1; // dppx based on clientY/screenY
+
+// Install global event listeners for mouse movements.
+function body_move_event (event)
+{
+  if (event.isTrusted &&
+      (!last_event || last_event.timeStamp <= event.timeStamp))
+    last_event = event;
+  // FF-122: clientX scales with devicePixelRatio, movementX and screenX scale with devicePixelRatio
+  // CR-120: clientX scales with devicePixelRatio, movementX and screenX remain unscaled
+}
+let last_event = null;
+document.body.addEventListener ("pointermove", CHROME_UA ? body_move_event_4chrome : body_move_event, { capture: true, passive: true });
+document.body.addEventListener ("pointerdown", body_move_event, { capture: true, passive: true });
+document.body.addEventListener ("pointerup", body_move_event, { capture: true, passive: true });
+
+/// Determine factor for Chrome to convert movementX to CSS px (based on event history)
+export function chrome_movement_factor()
+{
+  return chrome_dppx / devicePixelRatio;
+}
+
+/// Determine `movementX,movementY` in CSS pixels, independent of browser quirks.
+export function event_movement (event, shift_swaps = false)
+{
+  let mx = event.movementX, my = event.movementY;
+  if (CHROME_UA) {
+    const cf = chrome_movement_factor();
+    mx *= cf;
+    my *= cf;
+  }
+  let shiftSwapped = false;
+  if (shift_swaps && event.shiftKey) {
+    const tx = mx;
+    mx = my;
+    my = tx;
+    shiftSwapped = true;
+  }
+  return { movementX: mx, movementY: my, coalesced: event.getCoalescedEvents().length,
+	   shiftSwapped, shiftKey: event.shiftKey, ctrlKey: event.ctrlKey, altKey: event.altKey };
+  // FF-122: movementX,movementY values in getCoalescedEvents() are utterly broken
+}
+
+/// Determine mouse wheel deltas bare units, independent of zoom or DPI.
+export function wheel_delta (event, shift_swaps = false)
+{
+  // The delta values must be read *first* in FF, see: https://bugzilla.mozilla.org/show_bug.cgi?id=1392460#c33
+  let dx = event.deltaX, dy = event.deltaY, dz = event.deltaZ;
+  let dppx = CHROME_UA ? devicePixelRatio / Math.round (chrome_dppx) : 1;
+  if (event.deltaMode == WheelEvent.DOM_DELTA_LINE)
+    dppx *= 20;
+  else if (event.deltaMode == WheelEvent.DOM_DELTA_PAGE)
+    dppx *= 16 * 12;
+  dx *= dppx;
+  dy *= dppx;
+  dz *= dppx;
+  let shiftSwapped = false;
+  if (shift_swaps && event.shiftKey && dx == 0 && dy) {
+    dx = dy;
+    dy = 0;
+    shiftSwapped = true;
+  }
+  return { deltaX: dx, deltaY: dy, deltaZ: dz, deltaMode: WheelEvent.DOM_DELTA_PIXEL,
+	   shiftSwapped, shiftKey: event.shiftKey, ctrlKey: event.ctrlKey, altKey: event.altKey };
+  // FF-122: deltaY is mostly close to ±120 for mouse wheel on Linux regardless of zoom mode, and regardless of screen DPI
+  // CR-121: deltaY is ±120 for mouse wheel on Linux when devicePixelRatio=1, but is scaled along with zoom and screen DPI
+  // CR-120: deltaY is ±6 for touchpad on Linux
+}