--by exechack.cc Toxicbadkazuin
local length = 0.5 -- animation length.

local ease = 0.25 -- easing animation IN and OUT.

local amount = 30 -- scroll amount.

	local function sign( num )

		return num > 0

	end

	local function getBiggerPos( signOld, signNew, old, new )

		if signOld != signNew then return new end

		if signNew then

			return math.max(old, new)

		else

			return math.min(old, new)

		end

	end



	local dermaCtrs = vgui.GetControlTable( "DVScrollBar" )



	local tScroll = 0

	local newerT = 0



	function dermaCtrs:AddScroll( dlta )

	

		self.Old_Pos = nil

		self.Old_Sign = nil



		local OldScroll = self:GetScroll()



		dlta = dlta * amount

		

		local anim = self:NewAnimation( length, 0, ease )

		anim.StartPos = OldScroll

		anim.TargetPos = OldScroll + dlta + tScroll

		tScroll = tScroll + dlta



		local ctime = RealTime() -- does not work correctly with CurTime, when in single player game and in game menu (then CurTime get stuck). I think RealTime is better.

		local doing_scroll = true

		newerT = ctime

		

		anim.Think = function( anim, pnl, fraction )

			local nowpos = Lerp( fraction, anim.StartPos, anim.TargetPos )

			if ctime == newerT then

				self:SetScroll( getBiggerPos( self.Old_Sign, sign(dlta), self.Old_Pos, nowpos ) )

				tScroll = tScroll - (tScroll * fraction)

			end

			if doing_scroll then -- it must be here. if not, sometimes scroll get bounce.

				self.Old_Sign = sign(dlta)

				self.Old_Pos = nowpos

			end

			if ctime != newerT then doing_scroll = false end

		end



		return math.Clamp( self:GetScroll() + tScroll, 0, self.CanvasSize ) != self:GetScroll()



	end

	derma.DefineControl( "DVScrollBar", "Smooth Scrollbar", dermaCtrs, "Panel" )