From 35eb4e08dd53133abc14fdb189bfc9dd8fa848b7 Mon Sep 17 00:00:00 2001
From: myk002 <myk002@yahoo.com>
Date: Fri, 7 Oct 2022 15:40:05 -0700
Subject: [PATCH] hold down the mouse button to continue scrolling

---
 docs/Lua API.rst            | 12 +++++++++++
 docs/changelog.txt          |  1 +
 library/lua/gui/widgets.lua | 41 ++++++++++++++++++++++++++++++-------
 3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/docs/Lua API.rst b/docs/Lua API.rst
index ddb00c61a..8960cb15c 100644
--- a/docs/Lua API.rst	
+++ b/docs/Lua API.rst	
@@ -4064,6 +4064,18 @@ direction. The amount of scrolling done in each case in determined by the
 associated widget, and after scrolling is complete, the associated widget must
 call ``scrollbar:update()`` with updated new display info.
 
+You can hold down the mouse button to scroll multiple times, just like in a
+normal browser scrollbar. The speed of scroll events when the mouse button is
+held down is controlled by two global variables:
+
+:``SCROLL_INITIAL_DELAY_MS``: The delay before the second scroll event.
+:``SCROLL_DELAY_MS``: The delay between further scroll events.
+
+The defaults are 300 and 20, respectively, but they can be overridden by the
+user in their :file:`dfhack-config/init/dfhack.init` file, for example::
+
+  :lua require('gui.widgets').SCROLL_DELAY_MS = 100
+
 Label class
 -----------
 
diff --git a/docs/changelog.txt b/docs/changelog.txt
index b1d5300a9..1669ea9dd 100644
--- a/docs/changelog.txt
+++ b/docs/changelog.txt
@@ -42,6 +42,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 - `ls`: new ``--exclude`` option for hiding matched scripts from the output.  this can be especially useful for modders who don't want their mod scripts to be included in ``ls`` output.
 - `digtype`: new ``-z`` option for digtype to restrict designations to the current z-level and down
 - UX: List widgets now have mouse-interactive scrollbars
+- UX: You can now hold down the mouse button on a scrollbar to make it scroll multiple times.
 
 ## Documentation
 
diff --git a/library/lua/gui/widgets.lua b/library/lua/gui/widgets.lua
index 2eaf80577..e5b7e9bfd 100644
--- a/library/lua/gui/widgets.lua
+++ b/library/lua/gui/widgets.lua
@@ -363,6 +363,11 @@ end
 -- Scrollbar --
 ---------------
 
+-- these can be overridden by the user, e.g.:
+--   require('gui.widgets').SCROLL_DELAY_MS = 100
+SCROLL_INITIAL_DELAY_MS = 300
+SCROLL_DELAY_MS = 20
+
 Scrollbar = defclass(Scrollbar, Widget)
 
 Scrollbar.ATTRS{
@@ -377,6 +382,9 @@ function Scrollbar:preinit(init_table)
 end
 
 function Scrollbar:init()
+    self.last_scroll_ms = 0
+    self.is_first_click = false
+    self.scroll_spec = nil
     self:update(1, 1, 1)
 end
 
@@ -434,19 +442,38 @@ function Scrollbar:onRenderBody(dc)
     dc:seek(0, dc.height-1):char(
         last_visible_el >= self.num_elems and NO_ARROW_CHAR or DOWN_ARROW_CHAR,
         self.fg, self.bg)
+    -- manage state for continuous scrolling
+    if self.last_scroll_ms == 0 or not self.on_scroll then return end
+    if df.global.enabler.mouse_lbut_down == 0 then
+        self.last_scroll_ms = 0
+        self.scroll_spec = nil
+        return
+    end
+    local now = dfhack.getTickCount()
+    local delay = self.is_first_click and
+            SCROLL_INITIAL_DELAY_MS or SCROLL_DELAY_MS
+    if now - self.last_scroll_ms >= delay then
+        self.is_first_click = false
+        self.on_scroll(self.scroll_spec)
+        self.last_scroll_ms = now
+    end
 end
 
 function Scrollbar:onInput(keys)
     if not keys._MOUSE_L_DOWN or not self.on_scroll then return false end
     local _,y = self:getMousePos()
     if not y then return false end
-    local scroll = nil
-    if y == 0 then scroll = 'up_small'
-    elseif y == self.frame_body.height - 1 then scroll = 'down_small'
-    elseif y <= self.bar_offset then scroll = 'up_large'
-    elseif y > self.bar_offset + self.bar_height then scroll = 'down_large'
-    end
-    if scroll then self.on_scroll(scroll) end
+    local scroll_spec = nil
+    if y == 0 then scroll_spec = 'up_small'
+    elseif y == self.frame_body.height - 1 then scroll_spec = 'down_small'
+    elseif y <= self.bar_offset then scroll_spec = 'up_large'
+    elseif y > self.bar_offset + self.bar_height then scroll_spec = 'down_large'
+    end
+    self.scroll_spec = scroll_spec
+    if scroll_spec then self.on_scroll(scroll_spec) end
+    -- reset continuous scroll state
+    self.is_first_click = true
+    self.last_scroll_ms = dfhack.getTickCount()
     return true
 end