重构背景系统（每个背景使用独立文件），全局变量名整理

parts/backgrounds/space.lua

@@ -0,0 +1,48 @@
+--Space with stars
+local gc=love.graphics
+local rnd=math.random
+local back={}
+
+local stars
+local W,H
+function back.init()
+	stars={}
+	W,H=SCR.w+20,SCR.h+20
+	BG.resize(SCR.w,SCR.h)
+end
+function back.resize()
+	local S=stars
+	for i=1,1260,5 do
+		local s=rnd(26,40)*.1
+		S[i]=s*SCR.k			--Size
+		S[i+1]=rnd(W)-10		--X
+		S[i+2]=rnd(H)-10		--Y
+		S[i+3]=(rnd()-.5)*.01*s	--Vx
+		S[i+4]=(rnd()-.5)*.01*s	--Vy
+	end
+end
+function back.update()
+	local S=stars
+	--Star moving
+	for i=1,1260,5 do
+		S[i+1]=(S[i+1]+S[i+3])%W
+		S[i+2]=(S[i+2]+S[i+4])%H
+	end
+end
+function back.draw()
+	gc.clear(.2,.2,.2)
+	if not stars[1]then return end
+	gc.translate(-10,-10)
+	gc.setColor(.8,.8,.8)
+	for i=1,1260,5 do
+		local s=stars
+		local x,y=s[i+1],s[i+2]
+		s=s[i]
+		gc.rectangle("fill",x,y,s,s)
+	end
+	gc.translate(10,10)
+end
+function back.discard()
+	stars=nil
+end
+return back