refresh emulation: only update areas that are refreshed

when refresh emulation is enabled, only the parts of the screen
are actually updated that are being refreshed. This allows to
debug refresh regions with the emulator.
Reminder: activate refresh emulation by setting the environment
variable EMULATE_READER_FLASH to the number of milliseconds that
you want the inverse flash to endure. Suggested are now about
100 (msecs).

ffi/framebuffer_SDL1_2.lua

@@ -3,14 +3,25 @@ local SDL = require("ffi/SDL1_2")
 local BB = require("ffi/blitbuffer")
 local util = require("ffi/util")
 
-local framebuffer = {}
+local framebuffer = {
+    -- this blitbuffer will be used when we use refresh emulation
+    sdl_bb = nil,
+}
 
 function framebuffer:init()
 	if not self.dummy then
 		SDL.open()
-		-- we present this buffer to the outside
-		self.bb = BB.new(SDL.screen.w, SDL.screen.h, BB.TYPE_BBRGB32,
+		local bb = BB.new(SDL.screen.w, SDL.screen.h, BB.TYPE_BBRGB32,
 			SDL.screen.pixels, SDL.screen.pitch)
+        local flash = os.getenv("EMULATE_READER_FLASH")
+        if flash then
+            -- in refresh emulation mode, we use a shadow blitbuffer
+            -- and blit refresh areas from it.
+            self.sdl_bb = bb
+            self.bb = BB.new(SDL.screen.w, SDL.screen.h, BB.TYPE_BBRGB32)
+        else
+            self.bb = bb
+        end
 	else
 		self.bb = BB.new(600, 800)
 	end
@@ -46,10 +57,12 @@ function framebuffer:refreshFullImp(x, y, w, h)
 
     local flash = os.getenv("EMULATE_READER_FLASH")
     if flash then
-        bb:invertRect(x, y, w, h)
+        self.sdl_bb:invertRect(x, y, w, h)
         flip()
         util.usleep(tonumber(flash)*1000)
-        bb:invertRect(x, y, w, h)
+        self.sdl_bb:setRotation(bb:getRotation())
+        self.sdl_bb:setInverse(bb:getInverse())
+        self.sdl_bb:blitFrom(bb, x, y, x, y, w, h)
     end
 
     flip()

ffi/framebuffer_SDL2_0.lua

@@ -3,13 +3,25 @@ local SDL = require("ffi/SDL2_0")
 local BB = require("ffi/blitbuffer")
 local util = require("ffi/util")
 
-local framebuffer = {}
+local framebuffer = {
+    -- this blitbuffer will be used when we use refresh emulation
+    sdl_bb = nil,
+}
 
 function framebuffer:init()
     if not self.dummy then
 		SDL.open()
 		-- we present this buffer to the outside
-		self.bb = BB.new(SDL.w, SDL.h, BB.TYPE_BBRGB32)
+		local bb = BB.new(SDL.w, SDL.h, BB.TYPE_BBRGB32)
+        local flash = os.getenv("EMULATE_READER_FLASH")
+        if flash then
+            -- in refresh emulation mode, we use a shadow blitbuffer
+            -- and blit refresh areas from it.
+            self.sdl_bb = bb
+            self.bb = BB.new(SDL.w, SDL.h, BB.TYPE_BBRGB32)
+        else
+            self.bb = bb
+        end
 	else
 		self.bb = BB.new(600, 800)
     end
@@ -43,10 +55,12 @@ function framebuffer:refreshFullImp()
 
     local flash = os.getenv("EMULATE_READER_FLASH")
     if flash then
-        bb:invertRect(x, y, w, h)
+        self.sdl_bb:invertRect(x, y, w, h)
         render(bb)
         util.usleep(tonumber(flash)*1000)
-        bb:invertRect(x, y, w, h)
+        self.sdl_bb:setRotation(bb:getRotation())
+        self.sdl_bb:setInverse(bb:getInverse())
+        self.sdl_bb:blitFrom(bb, x, y, x, y, w, h)
     end
     render(bb)
 end