scrollcontainer: Add automatic scrollbar calculation (luanti-org#14623)

New parameter 'content padding'. When specified, the scrollbar
max value is calculated automatically. This aims to reduce manual
calculation functions.

Author: SmallJoker

builtin/mainmenu/settings/dlg_settings.lua

@@ -443,19 +443,6 @@ local function build_page_components(page)
 end
 
 
---- Creates a scrollbaroptions for a scroll_container
---
--- @param visible_l the length of the scroll_container and scrollbar
--- @param total_l length of the scrollable area
--- @param scroll_factor as passed to scroll_container
-local function make_scrollbaroptions_for_scroll_container(visible_l, total_l, scroll_factor)
-	assert(total_l >= visible_l)
-	local max = total_l - visible_l
-	local thumb_size = (visible_l / total_l) * max
-	return ("scrollbaroptions[min=0;max=%f;thumbsize=%f]"):format(max / scroll_factor, thumb_size / scroll_factor)
-end
-
-
 local formspec_show_hack = false
 
 
@@ -517,8 +504,8 @@ local function get_formspec(dialogdata)
 			"tooltip[search;", fgettext("Search"), "]",
 			"tooltip[search_clear;", fgettext("Clear"), "]",
 		"container_end[]",
-		"scroll_container[0.25,1.25;", tostring(left_pane_width), ",",
-				tostring(tabsize.height - 1.5), ";leftscroll;vertical;0.1]",
+		("scroll_container[0.25,1.25;%f,%f;leftscroll;vertical;0.1;0]"):format(
+			left_pane_width, tabsize.height - 1.5),
 		"style_type[button;border=false;bgcolor=#3333]",
 		"style_type[button:hover;border=false;bgcolor=#6663]",
 	}
@@ -548,7 +535,6 @@ local function get_formspec(dialogdata)
 	fs[#fs + 1] = "scroll_container_end[]"
 
 	if y >= tabsize.height - 1.25 then
-		fs[#fs + 1] = make_scrollbaroptions_for_scroll_container(tabsize.height - 1.5, y, 0.1)
 		fs[#fs + 1] = ("scrollbar[%f,1.25;%f,%f;vertical;leftscroll;%f]"):format(
 				left_pane_width + 0.25, scrollbar_w, tabsize.height - 1.5, dialogdata.leftscroll or 0)
 	end
@@ -560,7 +546,7 @@ local function get_formspec(dialogdata)
 	end
 
 	local right_pane_width = tabsize.width - left_pane_width - 0.375 - 2*scrollbar_w - 0.25
-	fs[#fs + 1] = ("scroll_container[%f,0;%f,%f;rightscroll;vertical;0.1]"):format(
+	fs[#fs + 1] = ("scroll_container[%f,0;%f,%f;rightscroll;vertical;0.1;0.25]"):format(
 			tabsize.width - right_pane_width - scrollbar_w, right_pane_width, tabsize.height)
 
 	y = 0.25
@@ -616,7 +602,6 @@ local function get_formspec(dialogdata)
 	fs[#fs + 1] = "scroll_container_end[]"
 
 	if y >= tabsize.height then
-		fs[#fs + 1] = make_scrollbaroptions_for_scroll_container(tabsize.height, y + 0.375, 0.1)
 		fs[#fs + 1] = ("scrollbar[%f,0;%f,%f;vertical;rightscroll;%f]"):format(
 				tabsize.width - scrollbar_w, scrollbar_w, tabsize.height, dialogdata.rightscroll or 0)
 	end

doc/lua_api.md

@@ -2747,6 +2747,8 @@ Version History
 * Formspec version 7 (5.8.0):
   * style[]: Add focused state for buttons
   * Add field_enter_after_edit[] (experimental)
+* Formspec version 8 (5.10.0)
+  * scroll_container[]: content padding parameter
 
 Elements
 --------
@@ -2830,7 +2832,7 @@ Elements
 * End of a container, following elements are no longer relative to this
   container.
 
-### `scroll_container[<X>,<Y>;<W>,<H>;<scrollbar name>;<orientation>;<scroll factor>]`
+### `scroll_container[<X>,<Y>;<W>,<H>;<scrollbar name>;<orientation>;<scroll factor>;<content padding>]`
 
 * Start of a scroll_container block. All contained elements will ...
   * take the scroll_container coordinate as position origin,
@@ -2839,6 +2841,12 @@ Elements
   * be clipped to the rectangle defined by `X`, `Y`, `W` and `H`.
 * `orientation`: possible values are `vertical` and `horizontal`.
 * `scroll factor`: optional, defaults to `0.1`.
+* `content padding`: (optional), in formspec coordinate units
+  * If specified, the scrollbar properties `max` and `thumbsize` are calculated automatically
+    based on the content size plus `content padding` at the end of the container. `min` is set to 0.
+  * Negative `scroll factor` is not supported.
+  * When active, `scrollbaroptions[]` has no effect on the affected properties.
+  * Defaults to empty value (= disabled).
 * Nesting is possible.
 * Some elements might work a little different if they are in a scroll_container.
 * Note: If you want the scroll_container to actually work, you also need to add a

games/devtest/mods/testformspec/formspec.lua

@@ -299,7 +299,18 @@ local scroll_fs =
 	"scrollbaroptions[max=170]".. -- lowest seen pos is: 0.1*170+6=23 (factor*max+height)
 	"scrollbar[7.5,0;0.3,4;vertical;scrbar;0]"..
 	"scrollbar[8,0;0.3,4;vertical;scrbarhmmm;0]"..
-	"dropdown[0,6;2;hmdrpdwnnn;Outside,of,container;1]"
+	"dropdown[0,6;2;hmdrpdwnnn;Outside,of,container;1]"..
+	"scroll_container[0,8;10,4;scrbar420;vertical;0.1;2]"..
+		"button[0.5,0.5;10,1;;Container with padding=2]"..
+		"list[current_player;main;0,5;8,4;]"..
+	"scroll_container_end[]"..
+	"scrollbar[10.1,8;0.5,4;vertical;scrbar420;0]"..
+	-- Buttons for scale comparison
+	"button[11,8;1,1;;0]"..
+	"button[11,9;1,1;;1]"..
+	"button[11,10;1,1;;2]"..
+	"button[11,11;1,1;;3]"..
+	"button[11,12;1,1;;4]"
 
 --style_type[label;textcolor=green]
 --label[0,0;Green]
@@ -462,7 +473,7 @@ mouse control = true]
 		]],
 
 	-- Scroll containers
-		"formspec_version[3]size[12,13]" ..
+		"formspec_version[7]size[12,13]" ..
 		scroll_fs,
 
 	-- Sound

src/gui/guiFormSpecMenu.cpp

@@ -356,7 +356,7 @@ void GUIFormSpecMenu::parseContainerEnd(parserData* data, const std::string &)
 void GUIFormSpecMenu::parseScrollContainer(parserData *data, const std::string &element)
 {
 	std::vector<std::string> parts;
-	if (!precheckElement("scroll_container start", element, 4, 5, parts))
+	if (!precheckElement("scroll_container start", element, 4, 6, parts))
 		return;
 
 	std::vector<std::string> v_pos  = split(parts[0], ',');
@@ -367,6 +367,12 @@ void GUIFormSpecMenu::parseScrollContainer(parserData *data, const std::string &
 	if (parts.size() >= 5 && !parts[4].empty())
 		scroll_factor = stof(parts[4]);
 
+	std::optional<s32> content_padding_px;
+	if (parts.size() >= 6 && !parts[5].empty()) {
+		std::vector<std::string> v_size = { parts[5], parts[5] };
+		content_padding_px = getRealCoordinateGeometry(v_size)[orientation == "vertical" ? 1 : 0];
+	}
+
 	MY_CHECKPOS("scroll_container", 0);
 	MY_CHECKGEOM("scroll_container", 1);
 
@@ -405,6 +411,7 @@ void GUIFormSpecMenu::parseScrollContainer(parserData *data, const std::string &
 
 	GUIScrollContainer *mover = new GUIScrollContainer(Environment,
 			clipper, spec_mover.fid, rect_mover, orientation, scroll_factor);
+	mover->setContentPadding(content_padding_px);
 
 	data->current_parent = mover;
 

src/gui/guiScrollBar.h

@@ -45,6 +45,7 @@ class GUIScrollBar : public IGUIElement
 	s32 getSmallStep() const { return small_step; }
 	s32 getPos() const;
 	s32 getTargetPos() const;
+	bool isHorizontal() const { return is_horizontal; }
 
 	void setMax(const s32 &max);
 	void setMin(const s32 &min);

src/gui/guiScrollContainer.cpp

@@ -67,6 +67,50 @@ void GUIScrollContainer::draw()
 	}
 }
 
+void GUIScrollContainer::setScrollBar(GUIScrollBar *scrollbar)
+{
+	m_scrollbar = scrollbar;
+
+	if (m_scrollbar && m_content_padding_px.has_value() && m_scrollfactor != 0.0f) {
+		// Set the scrollbar max value based on the content size.
+
+		// Get content size based on elements
+		core::rect<s32> size;
+		for (gui::IGUIElement *e : Children) {
+			core::rect<s32> abs_rect = e->getAbsolutePosition();
+			size.addInternalPoint(abs_rect.LowerRightCorner);
+		}
+
+		s32 visible_content_px = (
+			m_orientation == VERTICAL
+				? AbsoluteClippingRect.getHeight()
+				: AbsoluteClippingRect.getWidth()
+		);
+
+		s32 total_content_px = *m_content_padding_px + (
+			m_orientation == VERTICAL
+				? (size.LowerRightCorner.Y - AbsoluteClippingRect.UpperLeftCorner.Y)
+				: (size.LowerRightCorner.X - AbsoluteClippingRect.UpperLeftCorner.X)
+		);
+
+		s32 hidden_content_px = std::max<s32>(0, total_content_px - visible_content_px);
+		m_scrollbar->setMin(0);
+		m_scrollbar->setMax(std::ceil(hidden_content_px / std::fabs(m_scrollfactor)));
+
+		// Note: generally, the scrollbar has the same size as the scroll container.
+		// However, in case it isn't, proportional adjustments are needed.
+		s32 scrollbar_px = (
+			m_scrollbar->isHorizontal()
+				? m_scrollbar->getRelativePosition().getWidth()
+				: m_scrollbar->getRelativePosition().getHeight()
+		);
+
+		m_scrollbar->setPageSize((total_content_px * scrollbar_px) / visible_content_px);
+	}
+
+	updateScrolling();
+}
+
 void GUIScrollContainer::updateScrolling()
 {
 	s32 pos = m_scrollbar->getPos();

src/gui/guiScrollContainer.h

@@ -34,17 +34,18 @@ class GUIScrollContainer : public gui::IGUIElement
 
 	virtual void draw() override;
 
+	inline void setContentPadding(std::optional<s32> padding)
+	{
+		m_content_padding_px = padding;
+	}
+
 	inline void onScrollEvent(gui::IGUIElement *caller)
 	{
 		if (caller == m_scrollbar)
 			updateScrolling();
 	}
 
-	inline void setScrollBar(GUIScrollBar *scrollbar)
-	{
-		m_scrollbar = scrollbar;
-		updateScrolling();
-	}
+	void setScrollBar(GUIScrollBar *scrollbar);
 
 private:
 	enum OrientationEnum
@@ -56,7 +57,8 @@ class GUIScrollContainer : public gui::IGUIElement
 
 	GUIScrollBar *m_scrollbar;
 	OrientationEnum m_orientation;
-	f32 m_scrollfactor;
+	f32 m_scrollfactor; //< scrollbar pos * scrollfactor = scroll offset in pixels
+	std::optional<s32> m_content_padding_px; //< in pixels
 
 	void updateScrolling();
 };

src/network/networkprotocol.cpp

@@ -63,4 +63,4 @@
 const u16 LATEST_PROTOCOL_VERSION = 46;
 
 // See also formspec [Version History] in doc/lua_api.md
-const u16 FORMSPEC_API_VERSION = 7;
+const u16 FORMSPEC_API_VERSION = 8;