Merge #6428

6428: Extend `CScrollRegion` to support scrolling when mouse at edge r=def- a=Robyt3

Add `ScrollRelative` function to initiate relative scrolling programmatically, to realise scroll regions that scroll when the mouse is being dragged at the edge.

Add `DoEdgeScrolling` to encapsulate all the necessary edge scrolling logic based on the position of the mouse. The edge scrolling starts at a fixed distance from the edges. The scrolling speed is dependent on the distance of the mouse from this border.

## Checklist

- [X] Tested the change ingame (in combination with #6426)
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Robert Müller <robytemueller@gmail.com>

src/game/client/ui_scrollregion.cpp

@@ -13,11 +13,15 @@ CScrollRegion::CScrollRegion()
 {
 	m_ScrollY = 0.0f;
 	m_ContentH = 0.0f;
+	m_RequestScrollY = -1.0f;
+	m_ScrollDirection = SCROLLRELATIVE_NONE;
+	m_ScrollSpeedMultiplier = 1.0f;
+
 	m_AnimTimeMax = 0.0f;
 	m_AnimTime = 0.0f;
 	m_AnimInitScrollY = 0.0f;
 	m_AnimTargetScrollY = 0.0f;
-	m_RequestScrollY = -1.0f;
+
 	m_ContentScrollOff = vec2(0.0f, 0.0f);
 	m_Params = CScrollRegionParams();
 }
@@ -69,23 +73,30 @@ void CScrollRegion::End()
 	CUIRect RegionRect = m_ClipRect;
 	RegionRect.w += m_Params.m_ScrollbarWidth;
 
-	if(UI()->Enabled() && UI()->MouseHovered(&RegionRect))
+	if(m_ScrollDirection != SCROLLRELATIVE_NONE || (UI()->Enabled() && UI()->MouseHovered(&RegionRect)))
 	{
-		float ScrollDirection = 0.0f;
+		bool ProgrammaticScroll = false;
 		if(UI()->ConsumeHotkey(CUI::HOTKEY_SCROLL_UP))
-			ScrollDirection = -1.0f;
+			m_ScrollDirection = SCROLLRELATIVE_UP;
 		else if(UI()->ConsumeHotkey(CUI::HOTKEY_SCROLL_DOWN))
-			ScrollDirection = 1.0f;
+			m_ScrollDirection = SCROLLRELATIVE_DOWN;
+		else
+			ProgrammaticScroll = true;
 
-		if(ScrollDirection != 0.0f)
+		if(!ProgrammaticScroll)
+			m_ScrollSpeedMultiplier = 1.0f;
+
+		if(m_ScrollDirection != SCROLLRELATIVE_NONE)
 		{
 			const bool IsPageScroll = Input()->AltIsPressed();
-			const float ScrollUnit = IsPageScroll ? m_ClipRect.h : m_Params.m_ScrollUnit;
+			const float ScrollUnit = IsPageScroll && !ProgrammaticScroll ? m_ClipRect.h : m_Params.m_ScrollUnit;
 
 			m_AnimTimeMax = g_Config.m_UiSmoothScrollTime / 1000.0f;
 			m_AnimTime = m_AnimTimeMax;
 			m_AnimInitScrollY = m_ScrollY;
-			m_AnimTargetScrollY += ScrollDirection * ScrollUnit;
+			m_AnimTargetScrollY = (ProgrammaticScroll ? m_ScrollY : m_AnimTargetScrollY) + (int)m_ScrollDirection * ScrollUnit * m_ScrollSpeedMultiplier;
+			m_ScrollDirection = SCROLLRELATIVE_NONE;
+			m_ScrollSpeedMultiplier = 1.0f;
 		}
 	}
 
@@ -206,6 +217,28 @@ void CScrollRegion::ScrollHere(EScrollOption Option)
 	}
 }
 
+void CScrollRegion::ScrollRelative(EScrollRelative Direction, float SpeedMultiplier)
+{
+	m_ScrollDirection = Direction;
+	m_ScrollSpeedMultiplier = SpeedMultiplier;
+}
+
+void CScrollRegion::DoEdgeScrolling()
+{
+	if(!IsScrollbarShown())
+		return;
+
+	const float ScrollBorderSize = 20.0f;
+	const float MaxScrollMultiplier = 2.0f;
+	const float ScrollSpeedFactor = MaxScrollMultiplier / ScrollBorderSize;
+	const float TopScrollPosition = m_ClipRect.y + ScrollBorderSize;
+	const float BottomScrollPosition = m_ClipRect.y + m_ClipRect.h - ScrollBorderSize;
+	if(UI()->MouseY() < TopScrollPosition)
+		ScrollRelative(SCROLLRELATIVE_UP, minimum(MaxScrollMultiplier, (TopScrollPosition - UI()->MouseY()) * ScrollSpeedFactor));
+	else if(UI()->MouseY() > BottomScrollPosition)
+		ScrollRelative(SCROLLRELATIVE_DOWN, minimum(MaxScrollMultiplier, (UI()->MouseY() - BottomScrollPosition) * ScrollSpeedFactor));
+}
+
 bool CScrollRegion::IsRectClipped(const CUIRect &Rect) const
 {
 	return (m_ClipRect.x > (Rect.x + Rect.w) || (m_ClipRect.x + m_ClipRect.w) < Rect.x || m_ClipRect.y > (Rect.y + Rect.h) || (m_ClipRect.y + m_ClipRect.h) < Rect.y);

src/game/client/ui_scrollregion.h

@@ -86,10 +86,20 @@ Usage:
 // Instances of CScrollRegion must be static, as member addresses are used as UI item IDs
 class CScrollRegion : private CUIElementBase
 {
+public:
+	enum EScrollRelative
+	{
+		SCROLLRELATIVE_UP = -1,
+		SCROLLRELATIVE_NONE = 0,
+		SCROLLRELATIVE_DOWN = 1,
+	};
+
 private:
 	float m_ScrollY;
 	float m_ContentH;
 	float m_RequestScrollY; // [0, ContentHeight]
+	EScrollRelative m_ScrollDirection;
+	float m_ScrollSpeedMultiplier;
 
 	float m_AnimTimeMax;
 	float m_AnimTime;
@@ -116,6 +126,9 @@ public:
 	void End();
 	bool AddRect(const CUIRect &Rect, bool ShouldScrollHere = false); // returns true if the added rect is visible (not clipped)
 	void ScrollHere(EScrollOption Option = SCROLLHERE_KEEP_IN_VIEW);
+	void ScrollRelative(EScrollRelative Direction, float SpeedMultiplier = 1.0f);
+	const CUIRect *ClipRect() const { return &m_ClipRect; }
+	void DoEdgeScrolling();
 	bool IsRectClipped(const CUIRect &Rect) const;
 	bool IsScrollbarShown() const;
 	bool IsAnimating() const;