TextEditor: allow scrolling by lines with Pan (#4145)

Feature of ScrollTextWidget, only used for now by TextEditor.
Pan is like Swipe, but wait a bit at end of gesture to release:
the line on which Pan was started will be moved to where Pan is
released.

May conflict with MovableContainer (so not enabled for DictQuickLookup,
where it could have been nice - but it would work only with text
dictionaries, not with HTML ones, as ScrollHtmlWidget can't really
do that).

frontend/ui/widget/inputdialog.lua

@@ -128,6 +128,8 @@ local InputDialog = InputContainer:new{
         -- note that the text widget can be scrolled with Swipe North/South even when no button
     keyboard_hidden = false, -- start with keyboard hidden in full fullscreen mode
                              -- needs add_nav_bar to have a Show keyboard button to get it back
+    scroll_by_pan = false, -- allow scrolling by lines with Pan (= Swipe, but wait a bit at end
+                           -- of gesture before releasing) (may conflict with movable)
 
     -- If save_callback provided, a Save and a Close buttons will be added to the first row
     -- if reset_callback provided, a Reset button will be added (before Save) to the first row
@@ -359,6 +361,7 @@ function InputDialog:init()
         edit_callback = self._buttons_edit_callback, -- nil if no Save/Close buttons
         scroll_callback = self._buttons_scroll_callback, -- nil if no Nav or Scroll buttons
         scroll = true,
+        scroll_by_pan = self.scroll_by_pan,
         cursor_at_end = self.cursor_at_end,
         readonly = self.readonly,
         parent = self,

frontend/ui/widget/inputtext.lua

@@ -30,6 +30,7 @@ local InputText = InputContainer:new{
     parent = nil, -- parent dialog that will be set dirty
     edit_callback = nil, -- called with true when text modified, false on init or text re-set
     scroll_callback = nil, -- called with (low, high) when view is scrolled (cf ScrollTextWidget)
+    scroll_by_pan = false, -- allow scrolling by lines with Pan (needs scroll=true)
 
     width = nil,
     height = nil, -- when nil, will be set to original text height (possibly
@@ -322,6 +323,7 @@ function InputText:initTextBox(text, char_added)
             height = self.height,
             dialog = self.parent,
             scroll_callback = self.scroll_callback,
+            scroll_by_pan = self.scroll_by_pan,
         }
     else
         self.text_widget = TextBoxWidget:new{

frontend/ui/widget/scrolltextwidget.lua

@@ -9,6 +9,7 @@ local GestureRange = require("ui/gesturerange")
 local HorizontalGroup = require("ui/widget/horizontalgroup")
 local HorizontalSpan = require("ui/widget/horizontalspan")
 local InputContainer = require("ui/widget/container/inputcontainer")
+local Math = require("optmath")
 local TextBoxWidget = require("ui/widget/textboxwidget")
 local VerticalScrollBar = require("ui/widget/verticalscrollbar")
 local UIManager = require("ui/uimanager")
@@ -22,6 +23,8 @@ local ScrollTextWidget = InputContainer:new{
     top_line_num = nil,
     editable = false,
     justified = false,
+    scroll_callback = nil, -- called with (low, high) when view is scrolled
+    scroll_by_pan = false, -- allow scrolling by lines with Pan
     face = nil,
     fgcolor = Blitbuffer.COLOR_BLACK,
     width = Screen:scaleBySize(400),
@@ -79,6 +82,20 @@ function ScrollTextWidget:init()
                 },
             },
         }
+        if self.scroll_by_pan then
+            self.ges_events.PanText = {
+                GestureRange:new{
+                    ges = "pan",
+                    range = function() return self.dimen end,
+                },
+            }
+            self.ges_events.PanReleaseText = {
+                GestureRange:new{
+                    ges = "pan_release",
+                    range = function() return self.dimen end,
+                },
+            }
+        end
     end
     if Device:hasKeyboard() or Device:hasKeys() then
         self.key_events = {
@@ -235,4 +252,26 @@ function ScrollTextWidget:onScrollUp()
     return true
 end
 
+function ScrollTextWidget:onPanText(arg, ges)
+    self._pan_direction = ges.direction
+    self._pan_relative_x = ges.relative.x
+    self._pan_relative_y = ges.relative.y
+    return true
+end
+
+function ScrollTextWidget:onPanReleaseText(arg, ges)
+    if self._pan_direction and self._pan_relative_y then -- went thru onPanText
+        if self._pan_direction == "north" or self._pan_direction == "south" then
+            local nb_lines = Math.round(self._pan_relative_y / self:getLineHeight())
+            self.text_widget:scrollLines(-nb_lines)
+            self:updateScrollBar(true)
+        end
+        self._pan_direction = nil
+        self._pan_relative_x = nil
+        self._pan_relative_y = nil
+        return true
+    end
+    return false
+end
+
 return ScrollTextWidget

frontend/ui/widget/textboxwidget.lua

@@ -684,6 +684,32 @@ function TextBoxWidget:scrollUp()
     end
 end
 
+function TextBoxWidget:scrollLines(nb_lines)
+    -- nb_lines can be negative
+    if nb_lines == 0 then
+        return
+    end
+    self.image_show_alt_text = nil
+    local new_line_num = self.virtual_line_num + nb_lines
+    if new_line_num < 1 then
+        new_line_num = 1
+    end
+    if new_line_num > #self.vertical_string_list - self.lines_per_page + 1 then
+        new_line_num = #self.vertical_string_list - self.lines_per_page + 1
+    end
+    self.virtual_line_num = new_line_num
+    self:free()
+    self:_renderText(self.virtual_line_num, self.virtual_line_num + self.lines_per_page - 1)
+    if self.editable then
+        local x, y = self:_getXYForCharPos() -- luacheck: no unused
+        if y < 0 or y >= self.text_height then
+            -- move cursor to first line of visible area
+            local ln = self.height == nil and 1 or self.virtual_line_num
+            self:moveCursorToCharPos(self.vertical_string_list[ln] and self.vertical_string_list[ln].offset or 1)
+        end
+    end
+end
+
 function TextBoxWidget:scrollToTop()
     self.image_show_alt_text = nil
     if self.virtual_line_num > 1 then

plugins/texteditor.koplugin/main.lua

@@ -378,6 +378,7 @@ function TextEditor:editFile(file_path, readonly)
         cursor_at_end = false,
         readonly = readonly,
         add_nav_bar = true,
+        scroll_by_pan = true,
         buttons = is_lua and {{
             -- First button on first row, that will be filled with Reset|Save|Close
             {