From f9c9af6463705f66bac86d0a83939fb5166ac711 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 30 Jun 2020 09:50:15 +0530
Subject: [PATCH] Viewer: Fix turning pages in paged mode with a high precision
 touchpad to generate scroll events too fast

---
 src/pyj/read_book/flow_mode.pyj  | 19 ++-----------
 src/pyj/read_book/paged_mode.pyj | 47 ++++++++++++++++++++++++++++++--
 src/pyj/read_book/viewport.pyj   | 18 ++++++++++++
 3 files changed, 64 insertions(+), 20 deletions(-)

diff --git a/src/pyj/read_book/flow_mode.pyj b/src/pyj/read_book/flow_mode.pyj
index c625b910d7..05fa8402c9 100644
--- a/src/pyj/read_book/flow_mode.pyj
+++ b/src/pyj/read_book/flow_mode.pyj
@@ -5,25 +5,10 @@ from __python__ import bound_methods, hash_literals
 from dom import set_css
 from read_book.globals import current_spine_item, get_boss
 from read_book.settings import opts
-from read_book.viewport import scroll_viewport
+from read_book.viewport import line_height, scroll_viewport
 from utils import document_height, viewport_to_document
 
 
-def line_height():
-    if not line_height.ans:
-        ds = window.getComputedStyle(document.body)
-        try:
-            # will fail if line-height = "normal"
-            lh = float(ds.lineHeight)
-        except:
-            try:
-                lh = 1.2 * float(ds.fontSize)
-            except:
-                lh = 15
-        line_height.ans = max(5, lh)
-    return line_height.ans
-
-
 def flow_to_scroll_fraction(frac, on_initial_load):
     scroll_viewport.scroll_to(0, document_height() * frac)
 
@@ -209,7 +194,7 @@ def handle_shortcut(sc_name, evt):
 
 
 def layout(is_single_page):
-    line_height.ans = None
+    line_height(True)
     set_css(document.body, margin='0', border_width='0', padding='0')
 
 
diff --git a/src/pyj/read_book/paged_mode.pyj b/src/pyj/read_book/paged_mode.pyj
index d03accde4a..efa3490376 100644
--- a/src/pyj/read_book/paged_mode.pyj
+++ b/src/pyj/read_book/paged_mode.pyj
@@ -14,7 +14,7 @@ from read_book.cfi import (
 )
 from read_book.globals import current_spine_item, get_boss
 from read_book.settings import opts
-from read_book.viewport import scroll_viewport
+from read_book.viewport import scroll_viewport, line_height
 from utils import (
     document_height, document_width, get_elem_data, set_elem_data,
     viewport_to_document
@@ -170,6 +170,7 @@ def current_page_width():
 
 def layout(is_single_page, on_resize):
     nonlocal _in_paged_mode, col_width, col_and_gap, screen_height, gap, screen_width, is_full_screen_layout, cols_per_screen, number_of_cols
+    line_height(True)
     body_style = window.getComputedStyle(document.body)
     first_layout = not _in_paged_mode
     cps = calc_columns_per_screen()
@@ -293,6 +294,7 @@ def scroll_to_column(number, notify=False, duration=1000):
     pos = min(pos, limit)
     scroll_to_offset(pos)
 
+
 def scroll_to_xpos(xpos, notify=False, duration=1000):
     nonlocal last_scrolled_to_column
     # Scroll so that the column containing xpos is the left most column in
@@ -537,9 +539,43 @@ def is_return():
     return fsd and fsd.cols_per_screen is cols_per_screen and fsd.spine_index is csi.index and fsd.spine_name is csi.name
 
 
-def onwheel(evt):
-    if evt.deltaY:
+class HandleWheel:
+
+    def __init__(self):
+        self.reset()
+
+    def reset(self):
+        self.last_event_mode = 'page'
+        self.last_event_at = -10000
+        self.last_event_backwards = False
+        self.accumlated_scroll = 0
+
+    def onwheel(self, evt):
+        if not evt.deltaY:
+            return
         backward = evt.deltaY < 0
+        WheelEvent = window.WheelEvent
+        if evt.deltaMode is WheelEvent.DOM_DELTA_PAGE:
+            self.do_scroll(backward)
+        else:
+            self.add_event(backward, Math.abs(evt.deltaY), 'line' if evt.deltaMode is WheelEvent.DOM_DELTA_LINE else 'pixel')
+
+    def add_event(self, backward, deltaY, mode):
+        now = window.performance.now()
+        if now - self.last_event_at > 1000 or self.last_event_backwards is not backward or self.last_event_mode is not mode:
+            self.accumlated_scroll = 0
+        self.last_event_mode = mode
+        self.last_event_at = now
+        self.last_event_backwards = backward
+        lh = line_height()
+        if mode is 'line':
+            deltaY *= lh
+        self.accumlated_scroll += deltaY
+        if self.accumlated_scroll > 5 * lh:
+            self.do_scroll(backward)
+
+    def do_scroll(self, backward):
+        self.reset()
         if opts.paged_wheel_scrolls_by_screen:
             x = previous_screen_location() if backward else next_screen_location()
         else:
@@ -549,6 +585,11 @@ def onwheel(evt):
         else:
             scroll_to_xpos(x)
 
+
+wheel_handler = HandleWheel()
+onwheel = wheel_handler.onwheel.bind(wheel_handler)
+
+
 def scroll_by_page(backward, by_screen):
     if by_screen:
         pos = previous_screen_location() if backward else next_screen_location()
diff --git a/src/pyj/read_book/viewport.pyj b/src/pyj/read_book/viewport.pyj
index 7ef476d0e8..cdad564a30 100644
--- a/src/pyj/read_book/viewport.pyj
+++ b/src/pyj/read_book/viewport.pyj
@@ -113,3 +113,21 @@ for attr in FUNCTIONS:
     if not scroll_viewport['paged_' + attr]:
         scroll_viewport['paged_' + attr] = scroll_viewport[attr]
 viewport_mode_changer(scroll_viewport.set_mode)
+
+
+def line_height(reset):
+    if reset:
+        line_height.ans = None
+        return
+    if not line_height.ans:
+        ds = window.getComputedStyle(document.body)
+        try:
+            # will fail if line-height = "normal"
+            lh = float(ds.lineHeight)
+        except:
+            try:
+                lh = 1.2 * float(ds.fontSize)
+            except:
+                lh = 15
+        line_height.ans = max(5, lh)
+    return line_height.ans