From 8d838199c9bd423f666ac87d1a0bdc7282c61a25 Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Sun, 8 May 2016 09:34:48 +0200
Subject: [PATCH] Fix smooth scrolling speed in newer Firefox versions

The following pseudo-code used to work:

    setFirefoxSpringConstant()
    startScrollingSmoothly()
    resetFirefoxSpringConstant()
    // Some time later: Smooth scrolling finishes.

However, in some newer Firefox version that's changed.
`resetFirefoxSpringConstant` now has to be called when the smooth
scrolling is done, it seems. Unfortunately there appears to be no way of
knowing when that's the case. Instead, this commit introduces a timeout
before the spring constant pref is reset. The timeout can be customized
via the `scroll.reset_timeout` pref if needed. Special care was taken so
that, for example, holding `j` to scroll would only reset the pref
_once_ (after the last scroll command) and to the correct value.
---
 documentation/options.md      |  8 +++++++-
 extension/lib/commands.coffee | 24 ++++++++++++++++++++++--
 extension/lib/defaults.coffee |  1 +
 3 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/documentation/options.md b/documentation/options.md
index 0cacfa7..371efb7 100644
--- a/documentation/options.md
+++ b/documentation/options.md
@@ -310,10 +310,16 @@ These are VimFx’s variants, and the commands they affect:
 
 - `smoothScroll.lines.spring-constant`: `h`, `l`, `j`, `k`
 - `smoothScroll.pages.spring-constant`: `d`, `u`, `<space>`, `<s-space>`
-- `smoothScroll.other.spring-constant`: `gg`, `G`, `0`, `^`, `$`
+- `smoothScroll.other.spring-constant`: `gg`, `G`, `0`, `^`, `$`, `` ` ``
 
 Note that the value of these prefs are _strings,_ not numbers!
 
+Unfortunately, Firefox provides no way for code to tell which “spring constant”
+it wants when scrolling smoothly. All VimFx can do is to temporarily set
+Firefox’s `layout.css.scroll-behavior.spring-constant` pref. It is reset again
+after one second (by default). If that doesn’t work out for you, you can
+customize that timeout using the `scroll.reset_timeout` pref.
+
 The Firefox pref `general.smoothScroll` lets you turn off smooth scrolling
 entirely, including all of VimFx’s scrolling commands.
 
diff --git a/extension/lib/commands.coffee b/extension/lib/commands.coffee
index 323036a..55e6fd2 100644
--- a/extension/lib/commands.coffee
+++ b/extension/lib/commands.coffee
@@ -38,6 +38,8 @@ viewportUtils = require('./viewport')
 {ContentClick} = Cu.import('resource:///modules/ContentClick.jsm', {})
 {FORWARD, BACKWARD} = SelectionManager
 
+SPRING_CONSTANT_PREF = 'layout.css.scroll-behavior.spring-constant'
+
 commands = {}
 
 
@@ -143,6 +145,11 @@ commands.stop_all = ({vim}) ->
 
 
 
+springConstant = {
+  nonce: null
+  value: null
+}
+
 helper_scroll = (vim, uiEvent, args...) ->
   [
     method, type, directions, amounts
@@ -155,10 +162,23 @@ helper_scroll = (vim, uiEvent, args...) ->
       prefs.root.get("general.smoothScroll.#{type}")
     )
   }
-  reset = prefs.root.tmp(
-    'layout.css.scroll-behavior.spring-constant',
+
+  # Temporarily set Firefox’s “spring constant” pref to get the desired smooth
+  # scrolling speed. Reset it `reset_timeout` milliseconds after the last
+  # scrolling command was invoked.
+  springConstant.nonce = nonce = {}
+  springConstant.value ?= prefs.root.get(SPRING_CONSTANT_PREF)
+  prefs.root.set(
+    SPRING_CONSTANT_PREF,
     vim.options["smoothScroll.#{type}.spring-constant"]
   )
+  reset = ->
+    vim.window.setTimeout((->
+      return unless springConstant.nonce == nonce
+      prefs.root.set(SPRING_CONSTANT_PREF, springConstant.value)
+      springConstant.nonce = null
+      springConstant.value = null
+    ), vim.options.reset_timeout)
 
   helpScroll = help.getHelp(vim.window)?.querySelector('.wrapper')
   if uiEvent or helpScroll
diff --git a/extension/lib/defaults.coffee b/extension/lib/defaults.coffee
index 290facd..7eb496b 100644
--- a/extension/lib/defaults.coffee
+++ b/extension/lib/defaults.coffee
@@ -170,6 +170,7 @@ advanced_options =
   'smoothScroll.lines.spring-constant': '1000'
   'smoothScroll.pages.spring-constant': '2500'
   'smoothScroll.other.spring-constant': '2500'
+  'scroll.reset_timeout':               1000
   'scroll.full_page_adjustment':        40
   'scroll.half_page_adjustment':        20
   'scroll.last_position_mark':          '`'
-- 
2.39.3