support scrolling by half pages in Label

docs/Lua API.rst

@@ -3928,11 +3928,14 @@ It has the following attributes:
 :auto_width: Sets self.frame.w from the text width.
 :on_click: A callback called when the label is clicked (optional)
 :on_rclick: A callback called when the label is right-clicked (optional)
-:scroll_keys: Specifies which keys the label should react to as a table. Default is ``STANDARDSCROLL`` (up or down arrows, page up or down).
+:scroll_keys: Specifies which keys the label should react to as a table. The table should map
+    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
-     icons next to the text in an additional column (``frame_inset`` is adjusted to have ``.r`` or ``.l`` greater than ``0``),
+    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
+    ``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``.
+    (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``.
@@ -4024,6 +4027,12 @@ The Label widget implements the following methods:
 
   Computes the width of the text.
 
+* ``label:scroll(nlines)``
+
+  This method takes the number of lines to scroll as positive or negative
+  integers or one of the following keywords: ``+page``, ``-page``,
+  ``+halfpage``, or ``-halfpage``.
+
 WrappedLabel class
 ------------------
 

library/lua/gui/widgets.lua

@@ -652,6 +652,19 @@ function Label:onRenderFrame(dc, rect)
 end
 
 function Label:scroll(nlines)
+    if type(nlines) == 'string' then
+        if nlines == '+page' then
+            nlines = self.frame_body.height
+        elseif nlines == '-page' then
+            nlines = -self.frame_body.height
+        elseif nlines == '+halfpage' then
+            nlines = math.ceil(self.frame_body.height/2)
+        elseif nlines == '-halfpage' then
+            nlines = -math.ceil(self.frame_body.height/2)
+        else
+            error(('unhandled scroll keyword: "%s"'):format(nlines))
+        end
+    end
     local n = self.start_line_num + nlines
     n = math.min(n, self:getTextHeight() - self.frame_body.height + 1)
     n = math.max(n, 1)
@@ -668,11 +681,6 @@ function Label:onInput(keys)
     end
     for k,v in pairs(self.scroll_keys) do
         if keys[k] then
-            if v == '+page' then
-                v = self.frame_body.height
-            elseif v == '-page' then
-                v = -self.frame_body.height
-            end
             self:scroll(v)
         end
     end

test/library/gui/widgets.Label.lua

@@ -18,7 +18,7 @@ function test.correct_frame_body_with_scroll_icons()
         t[#t+1] = NEWLINE
     end
 
-    function fs:init(args)
+    function fs:init()
         self:addviews{
             widgets.Label{
                 view_id = 'text',
@@ -39,7 +39,7 @@ function test.correct_frame_body_with_few_text_lines()
         t[#t+1] = NEWLINE
     end
 
-    function fs:init(args)
+    function fs:init()
         self:addviews{
             widgets.Label{
                 view_id = 'text',
@@ -60,7 +60,7 @@ function test.correct_frame_body_without_show_scroll_icons()
         t[#t+1] = NEWLINE
     end
 
-    function fs:init(args)
+    function fs:init()
         self:addviews{
             widgets.Label{
                 view_id = 'text',
@@ -74,3 +74,43 @@ function test.correct_frame_body_without_show_scroll_icons()
     local o = fs{}
     expect.eq(o.subviews.text.frame_body.width, 10, "Label's frame_body.x2 and .width should not change with show_scroll_icons = false.")
 end
+
+function test.scroll()
+    local t = {}
+    for i = 1, 12 do
+        t[#t+1] = tostring(i)
+        t[#t+1] = NEWLINE
+    end
+
+    function fs:init()
+        self:addviews{
+            widgets.Label{
+                view_id = 'text',
+                frame_inset = 0,
+                text = t,
+            },
+        }
+    end
+
+    local o = fs{frame_height=3}
+    local txt = o.subviews.text
+    expect.eq(1, txt.start_line_num)
+    
+    txt:scroll(1)
+    expect.eq(2, txt.start_line_num)
+    txt:scroll('+page')
+    expect.eq(5, txt.start_line_num)
+    txt:scroll('+halfpage')
+    expect.eq(7, txt.start_line_num)
+    txt:scroll('-halfpage')
+    expect.eq(5, txt.start_line_num)
+    txt:scroll('-page')
+    expect.eq(2, txt.start_line_num)
+    txt:scroll(-1)
+    expect.eq(1, txt.start_line_num)
+
+    txt:scroll(-1)
+    expect.eq(1, txt.start_line_num)
+    txt:scroll(100)
+    expect.eq(10, txt.start_line_num)
+end