simplify style system

luigi/backend/ffisdl.lua

@@ -85,6 +85,7 @@ Backend.run = function ()
             end
         end
 
+        sdl.renderSetClipRect(renderer, nil)
         sdl.setRenderDrawColor(renderer, 0, 0, 0, 255)
         sdl.renderClear(renderer)
         callback.draw()
@@ -273,8 +274,6 @@ local stack = {}
 Backend.pop = function ()
     local history = stack[#stack]
     local color = history.color or { 0, 0, 0, 255 }
-    Backend.setColor(history.color or { 0, 0, 0, 255 })
-    Backend.sdl = sdl
 
     sdl.setRenderDrawColor(renderer,
         color[1], color[2], color[3], color[4] or 255)