show full scrollbars instead of just scroll icons

docs/Lua API.rst

@@ -4039,13 +4039,12 @@ It has the following attributes:
     keys to the number of lines to scroll as positive or negative integers or one of the keywords
     supported by the ``scroll`` method. The default is up/down arrows scrolling by one line and page
     up/down scrolling by one page.
-:show_scroll_icons: Controls scroll icons' behaviour: ``false`` for no icons, ``'right'`` or ``'left'`` for
+:show_scrollbar: Controls scrollbar display: ``false`` for no scrollbar, ``'right'`` or ``'left'`` for
     icons next to the text in an additional column (``frame_inset`` is adjusted to have ``.r`` or ``.l`` greater than ``0``),
     ``nil`` same as ``'right'`` but changes ``frame_inset`` only if a scroll icon is actually necessary
     (if ``getTextHeight()`` is greater than ``frame_body.height``). Default is ``nil``.
-:up_arrow_icon: The symbol for scroll up arrow. Default is ``string.char(24)`` (``↑``).
-:down_arrow_icon: The symbol for scroll down arrow. Default is ``string.char(25)`` (``↓``).
-:scroll_icon_pen: Specifies the pen for scroll icons. Default is ``COLOR_LIGHTCYAN``.
+:scrollbar_fg: Specifies the pen for the scroll icons and the active part of the bar. Default is ``COLOR_LIGHTGREEN`` (the same as the native DF help screens).
+:scrollbar_bg: Specifies the pen for the background part of the scrollbar. Default is ``COLOR_CYAN`` (the same as the native DF help screens).
 
 The text itself is represented as a complex structure, and passed
 to the object via the ``text`` argument of the constructor, or via

docs/changelog.txt

@@ -64,6 +64,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 - `seedwatch`: ``seedwatch all`` now adds all plants with seeds to the watchlist, not just the "basic" crops.
 - UX: You can now move the cursor around in DFHack text fields in ``gui/`` scripts (e.g. `gui/blueprint`, `gui/quickfort`, or `gui/gm-editor`). You can move the cursor by clicking where you want it to go with the mouse or using the Left/Right arrow keys.  Ctrl+Left/Right will move one word at a time, and Alt+Left/Right will move to the beginning/end of the text.
 - UX: You can now click on the hotkey hint text in many ``gui/`` script windows to activate the hotkey, like a button. Not all scripts have been updated to use the clickable widget yet, but you can try it in `gui/blueprint` or `gui/quickfort`.
+- UX: Label widget scroll icons are replaced with scrollbars that represent the percentage of text on the screen and move with the position of the visible text, just like web browser scrollbars.
 - `quickfort`: `Dreamfort <quickfort-blueprint-guide>` blueprint set improvements: set traffic designations to encourage dwarves to eat cooked food instead of raw ingredients
 
 ## Documentation

library/lua/gui/widgets.lua

@@ -544,12 +544,10 @@ Label.ATTRS{
     auto_width = false,
     on_click = DEFAULT_NIL,
     on_rclick = DEFAULT_NIL,
-    --
     scroll_keys = STANDARDSCROLL,
-    show_scroll_icons = DEFAULT_NIL, -- DEFAULT_NIL, 'right', 'left', false
-    up_arrow_icon = string.char(24),
-    down_arrow_icon = string.char(25),
-    scroll_icon_pen = COLOR_LIGHTCYAN,
+    show_scrollbar = DEFAULT_NIL, -- DEFAULT_NIL, 'right', 'left', false
+    scrollbar_fg = COLOR_LIGHTGREEN,
+    scrollbar_bg = COLOR_CYAN
 }
 
 function Label:init(args)
@@ -573,16 +571,16 @@ function Label:setText(text)
 end
 
 function Label:update_scroll_inset()
-    if self.show_scroll_icons == nil then
-        self._show_scroll_icons = self:getTextHeight() > self.frame_body.height and 'right' or false
+    if self.show_scrollbar == nil then
+        self._show_scrollbar = self:getTextHeight() > self.frame_body.height and 'right' or false
     else
-        self._show_scroll_icons = self.show_scroll_icons
+        self._show_scrollbar = self.show_scrollbar
     end
-    if self._show_scroll_icons then
-        -- here self._show_scroll_icons can only be either
+    if self._show_scrollbar then
+        -- here self._show_scrollbar can only be either
         -- 'left' or any true value which we interpret as right
         local l,t,r,b = gui.parse_inset(self.frame_inset)
-        if self._show_scroll_icons == 'left' and l <= 0 then
+        if self._show_scrollbar == 'left' and l <= 0 then
             l = 1
         elseif r <= 0 then
             r = 1
@@ -591,14 +589,54 @@ function Label:update_scroll_inset()
     end
 end
 
-function Label:render_scroll_icons(dc, x, y1, y2)
-    if self.start_line_num ~= 1 then
-        dc:seek(x, y1):char(self.up_arrow_icon, self.scroll_icon_pen)
+-- the position is the number of tiles of empty space above the top of the
+-- scrollbar, and the height is the number of tiles the scrollbar should occupy
+-- to represent the percentage of text that is on the screen.
+local function get_scrollbar_pos_and_height(label)
+    local first_visible_line = label.start_line_num
+    local text_height = label:getTextHeight()
+    local last_visible_line = first_visible_line + label.frame_body.height - 1
+    local scrollbar_body_height = label.frame_body.height - 2
+    local displayed_lines = last_visible_line - first_visible_line
+
+    local height = math.min(scrollbar_body_height - 1,
+        math.ceil((displayed_lines-1) * scrollbar_body_height / text_height))
+
+    local max_pos = scrollbar_body_height - height
+    local pos = math.ceil(((first_visible_line-1) * max_pos) /
+                          (text_height - label.frame_body.height))
+
+    return pos, height
+end
+
+local UP_ARROW_CHAR = string.char(24)
+local DOWN_ARROW_CHAR = string.char(25)
+local NO_ARROW_CHAR = string.char(32)
+local BAR_CHAR = string.char(7)
+local BAR_BG_CHAR = string.char(179)
+
+function Label:render_scrollbar(dc, x, y1, y2)
+    -- render up arrow if we're not at the top
+    dc:seek(x, y1):char(
+        self.start_line_num == 1 and NO_ARROW_CHAR or UP_ARROW_CHAR,
+        self.scrollbar_fg, self.scrollbar_bg)
+    -- render scrollbar body
+    local pos, height = get_scrollbar_pos_and_height(self)
+    local starty = y1 + pos + 1
+    local endy = y1 + pos + height
+    for y=y1+1,y2-1 do
+        if y >= starty and y <= endy then
+            dc:seek(x, y):char(BAR_CHAR, self.scrollbar_fg)
+        else
+            dc:seek(x, y):char(BAR_BG_CHAR, self.scrollbar_bg)
+        end
     end
+    -- render down arrow if we're not at the bottom
     local last_visible_line = self.start_line_num + self.frame_body.height - 1
-    if last_visible_line < self:getTextHeight() then
-        dc:seek(x, y2):char(self.down_arrow_icon, self.scroll_icon_pen)
-    end
+    dc:seek(x, y2):char(
+        last_visible_line >= self:getTextHeight() and
+            NO_ARROW_CHAR or DOWN_ARROW_CHAR,
+        self.scrollbar_fg, self.scrollbar_bg)
 end
 
 function Label:computeFrame(parent_rect)
@@ -644,13 +682,13 @@ function Label:onRenderBody(dc)
 end
 
 function Label:onRenderFrame(dc, rect)
-    if self._show_scroll_icons
+    if self._show_scrollbar
     and self:getTextHeight() > self.frame_body.height
     then
-        local x = self._show_scroll_icons == 'left'
+        local x = self._show_scrollbar == 'left'
                 and self.frame_body.x1-dc.x1-1
                 or  self.frame_body.x2-dc.x1+1
-        self:render_scroll_icons(dc,
+        self:render_scrollbar(dc,
             x,
             self.frame_body.y1-dc.y1,
             self.frame_body.y2-dc.y1