browser_window_position_precision.js

Enable keyboard shortcuts

/* Any copyright is dedicated to the Public Domain.

   http://creativecommons.org/publicdomain/zero/1.0/ */

"use strict";

// Test that window positions are properly restored when DPI is such that CSS

// pixel math would lead to roundoff error (but device pixel math does not).

// We use 1.25 device pixels per CSS pixel: a desktop-pixel position is a whole

// number of CSS pixels only if it is a multiple of 5.

const DEV_PIXELS_PER_PX = 1.25;

const CSS_PIXEL_PERIOD = 5;

function getPositionInDesktopPix(win) {

  const baseWindow = win.docShell.treeOwner.QueryInterface(Ci.nsIBaseWindow);

  const x = {},

    y = {};

  baseWindow.getPosition(x, y);

  const scale = baseWindow.devicePixelsPerDesktopPixel;

  return { x: x.value / scale, y: y.value / scale };

add_task(async function test_position_survives_round_trip() {

  // Force a fractional number of device pixels per CSS pixel.

  await SpecialPowers.pushPrefEnv({

    set: [["layout.css.devPixelsPerPx", String(DEV_PIXELS_PER_PX)]],

});

  const win = await BrowserTestUtils.openNewBrowserWindow();

  try {

    // Positions are only saved from, and restored to, windows in the normal

    // size mode.

    if (win.windowState != win.STATE_NORMAL) {

      const sizeModeChanged = BrowserTestUtils.waitForEvent(

        win,

        "sizemodechange"

);

      win.restore();

      await sizeModeChanged;

    const pos = getPositionInDesktopPix(win);

    // Pick a target which is deliberately not a whole number of CSS pixels.

    let targetX = pos.x + 1;

    if (targetX % CSS_PIXEL_PERIOD == 0) {

      targetX += 1;

    isnot(

      targetX % CSS_PIXEL_PERIOD,

0,

      "Test target should not land on a whole CSS pixel"

);

    const state = ss.getWindowState(win);

is(

      state.windows[0].screenX,

      pos.x,

      "Saved screenX should be the window's exact desktop-pixel position"

);

    state.windows[0].screenX = targetX;

    ss.setWindowState(win, JSON.stringify(state), false);

    await TestUtils.waitForCondition(

      () => getPositionInDesktopPix(win).x == targetX,

      `Window should be restored to exactly ${targetX} desktop px`

);

is(

      ss.getWindowState(win).windows[0].screenX,

      targetX,

      "Restored position should be saved back unchanged"

);

  } finally {

    await BrowserTestUtils.closeWindow(win);

});