Improve auto-scrolling after pasting very large documents

There were 2 problems.

When pasting very large documents, the height calculations will be
temporarily incorrect while the content is rendered over several frames.
This is addressed by waiting for the UI to be idle to scroll.

Additionally, the scroll time (typically 200ms) needs an adjustment as
well. Starting at 200ms, it now scales linearly with distance, amounting
to roughly 4 seconds with Pandoc's user guide.

uberwriter/scroller.py

@@ -1,47 +1,47 @@
 class Scroller:
-    def __init__(self, scrolled_window, target_pos, source_pos, duration=2000):
+    def __init__(self, scrolled_window, source_pos, target_pos):
         super().__init__()
 
         self.scrolled_window = scrolled_window
-        self.target_pos = target_pos
         self.source_pos = source_pos
-        self.duration = duration
+        self.target_pos = target_pos
+        self.duration = max(200, (target_pos - source_pos) / 50) * 1000
 
         self.is_started = False
+        self.is_setup = False
         self.start_time = 0
         self.end_time = 0
-
         self.tick_callback_id = 0
 
     def start(self):
-        self.tick_callback_id = self.scrolled_window.add_tick_callback(self.on_tick, self)
+        self.is_started = True
+        self.tick_callback_id = self.scrolled_window.add_tick_callback(self.on_tick)
 
     def end(self):
-        self.is_started = False
         self.scrolled_window.remove_tick_callback(self.tick_callback_id)
+        self.is_started = False
 
-    def do_start(self, time):
-        self.is_started = True
+    def setup(self, time):
         self.start_time = time
-        self.end_time = time + self.duration * 100
+        self.end_time = time + self.duration
+        self.is_setup = True
 
-    @staticmethod
-    def on_tick(widget, frame_clock, scroller):
+    def on_tick(self, widget, frame_clock):
         def ease_out_cubic(value):
             return pow(value - 1, 3) + 1
 
         now = frame_clock.get_frame_time()
-        if not scroller.is_started:
-            scroller.do_start(now)
+        if not self.is_setup:
+            self.setup(now)
 
-        if now < scroller.end_time:
-            time = float(now - scroller.start_time) / float(scroller.end_time - scroller.start_time)
+        if now < self.end_time:
+            time = float(now - self.start_time) / float(self.end_time - self.start_time)
         else:
             time = 1
-            scroller.end()
+            self.end()
 
         time = ease_out_cubic(time)
-        pos = scroller.source_pos + (time * (scroller.target_pos - scroller.source_pos))
+        pos = self.source_pos + (time * (self.target_pos - self.source_pos))
         widget.get_vadjustment().props.value = pos
         return True
 

uberwriter/text_view.py

@@ -8,7 +8,7 @@ from uberwriter.text_view_drag_drop_handler import DragDropHandler, TARGET_URI,
 from uberwriter.scroller import Scroller
 
 gi.require_version('Gtk', '3.0')
-from gi.repository import Gtk, Gdk, GObject
+from gi.repository import Gtk, Gdk, GObject, GLib
 
 import logging
 LOGGER = logging.getLogger('uberwriter')
@@ -104,7 +104,7 @@ class TextView(Gtk.TextView):
 
     def on_text_changed(self, *_):
         self.markup.apply()
-        self.scroll_to()
+        GLib.idle_add(self.scroll_to)
 
     def on_size_allocate(self, *_):
         self.update_vertical_margin()
@@ -186,7 +186,7 @@ class TextView(Gtk.TextView):
         if self.scroller and self.scroller.is_started:
             self.scroller.end()
         if target_pos:
-            self.scroller = Scroller(scrolled_window, target_pos, va.props.value)
+            self.scroller = Scroller(scrolled_window, va.props.value, target_pos)
             self.scroller.start()
 
     def on_mark_set(self, _text_buffer, _location, mark, _data=None):