升级SCR模块，整理大量坐标系变换代码

parts/backgrounds/blockrain.lua

@@ -41,15 +41,12 @@ function back.update()
 end
 function back.draw()
 	gc.clear(.1,.1,.1)
-	gc.push('transform')
-	gc.origin()
 	for i=1,#mino do
 		local C=mino[i]
 		local c=C.color
 		gc.setColor(c[1],c[2],c[3],.2)
 		gc.draw(C.block,C.x,C.y,C.ang,C.k,C.k,C.block:getWidth()/2,C.block:getHeight()/2)
 	end
-	gc.pop()
 end
 function back.discard()
 	mino=nil