[UX] Dict: scroll back with tap: go to bottom of prev definition (#3647)

frontend/ui/widget/dictquicklookup.lua

@@ -697,7 +697,13 @@ function DictQuickLookup:onTapCloseDict(arg, ges_ev)
     -- will pop it up for us here when it can't scroll anymore).
     -- This allow for continuous reading of results' definitions with tap.
     if ges_ev.pos.x < Screen:getWidth()/2 then
+        local prev_index = self.dict_index
         self:changeToPrevDict()
+        if self.dict_index ~= prev_index then
+            -- Jump directly to bottom of previous dict definition
+            -- to keep "continuous reading with tap" consistent
+            self.definition_widget[1]:scrollToRatio(1) -- 1 = 100% = bottom
+        end
     else
         self:changeToNextDict()
     end

frontend/ui/widget/scrollhtmlwidget.lua

@@ -11,7 +11,7 @@ local HorizontalSpan = require("ui/widget/horizontalspan")
 local InputContainer = require("ui/widget/container/inputcontainer")
 local UIManager = require("ui/uimanager")
 local VerticalScrollBar = require("ui/widget/verticalscrollbar")
-
+local Math = require("optmath")
 local Input = Device.input
 local Screen = Device.screen
 
@@ -82,6 +82,21 @@ function ScrollHtmlWidget:init()
     end
 end
 
+function ScrollHtmlWidget:scrollToRatio(ratio)
+    ratio = math.max(0, math.min(1, ratio)) -- ensure ratio is between 0 and 1 (100%)
+    local page_num = 1 + Math.round((self.htmlbox_widget.page_count - 1) * ratio)
+    if page_num == self.htmlbox_widget.page_number then
+        return
+    end
+    self.htmlbox_widget.page_number = page_num
+    self.v_scroll_bar:set((page_num-1) / self.htmlbox_widget.page_count, page_num / self.htmlbox_widget.page_count)
+    self.htmlbox_widget:freeBb()
+    self.htmlbox_widget:_render()
+    UIManager:setDirty(self.dialog, function()
+        return "partial", self.dimen
+    end)
+end
+
 function ScrollHtmlWidget:scrollText(direction)
     if direction == 0 then
         return

frontend/ui/widget/scrolltextwidget.lua

@@ -110,6 +110,14 @@ function ScrollTextWidget:scrollText(direction)
     end)
 end
 
+function ScrollTextWidget:scrollToRatio(ratio)
+    local low, high = self.text_widget:scrollToRatio(ratio)
+    self.v_scroll_bar:set(low, high)
+    UIManager:setDirty(self.dialog, function()
+        return "partial", self.dimen
+    end)
+end
+
 function ScrollTextWidget:onScrollText(arg, ges)
     if ges.direction == "north" then
         self:scrollText(1)

frontend/ui/widget/textboxwidget.lua

@@ -26,6 +26,7 @@ local Size = require("ui/size")
 local TextWidget = require("ui/widget/textwidget")
 local TimeVal = require("ui/timeval")
 local UIManager = require("ui/uimanager")
+local Math = require("optmath")
 local logger = require("logger")
 local util = require("util")
 local Screen = require("device").screen
@@ -643,6 +644,21 @@ function TextBoxWidget:scrollUp()
     return (self.virtual_line_num - 1) / #self.vertical_string_list, (self.virtual_line_num - 1 + visible_line_count) / #self.vertical_string_list
 end
 
+function TextBoxWidget:scrollToRatio(ratio)
+    self.image_show_alt_text = nil
+    ratio = math.max(0, math.min(1, ratio)) -- ensure ratio is between 0 and 1 (100%)
+    local visible_line_count = self:getVisLineCount()
+    local page_count = 1 + math.floor((#self.vertical_string_list - 1) / visible_line_count)
+    local page_num = 1 + Math.round((page_count - 1) * ratio)
+    local line_num = 1 + (page_num - 1) * visible_line_count
+    if line_num ~= self.virtual_line_num then
+        self:free()
+        self.virtual_line_num = line_num
+        self:_renderText(self.virtual_line_num, self.virtual_line_num + visible_line_count - 1)
+    end
+    return (self.virtual_line_num - 1) / #self.vertical_string_list, (self.virtual_line_num - 1 + visible_line_count) / #self.vertical_string_list
+end
+
 function TextBoxWidget:getSize()
     if self.width and self.height then
         return Geom:new{ w = self.width, h = self.height}