From ea597e505a69974dfd35dd2728b1e9f3bb109fa9 Mon Sep 17 00:00:00 2001
From: Matthijs Kooijman <matthijs@stdin.nl>
Date: Mon, 24 Aug 2009 20:24:33 +0200
Subject: [PATCH] Add a backbuffer for the created window.

This backbuffer is copied to the window on every expose event, but
nothing is draw on it yet.
---
 FPPrac.hs | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/FPPrac.hs b/FPPrac.hs
index 47b3cad..79a6a0a 100644
--- a/FPPrac.hs
+++ b/FPPrac.hs
@@ -99,6 +99,7 @@ testProg = Main
 
 data IState = forall s. IS
 	{ window    :: Gtk.Window
+	, buffer    :: IORef Cairo.Surface
 	, postponed :: IORef [Request]
 	, usrState  :: IORef s
 	, usrProg   :: TinaStep s
@@ -132,11 +133,11 @@ runTina :: TinaProgram -> IO ()
 runTina Main {..} = do
 	usrState  <- newIORef initialState
 	postponed <- newIORef (GfxText (rgb 0 0 0) (pt 50 50) "foo" : GfxClear :initialRequests)
-	let state = IS { window = undefined, usrProg = eventHandler, .. }
+	let state = IS { window = undefined, buffer = undefined, usrProg = eventHandler, .. }
 	runGUI windowWidth windowHeight state
 
 runGUI :: Int -> Int -> IState -> IO ()
-runGUI w h s = do
+runGUI w h (IS { .. }) = do
 	-- Init GTK.
 	Gtk.initGUI
 	
@@ -150,14 +151,36 @@ runGUI w h s = do
 		       , Gtk.windowDefaultHeight := h
 	               ]
 	Gtk.onDestroy window Gtk.mainQuit
-
-	-- Add the window to the state
-	let state = s { window = window }
 	
+	-- Create a buffer to draw on (name the actual buffer buffer', so we
+	-- can use IS { .. } syntax below to pack the state. Using a record update
+	-- wouldn't work, probably because Cairo.Surface contains an existential
+	-- type...
+	-- We put the buffer in an IORef, so we can change it for a new one
+	-- later on (on window resizes).
+	buffer' <- Cairo.createImageSurface Cairo.FormatARGB32 w h
+	buffer <- newIORef buffer'
+
+	-- Register the expose event
+	Gtk.on window Gtk.exposeEvent $ onExpose buffer
+
+	-- Repack state
+	let state = IS { .. }
+		
 	-- Show the window and start the Gtk mainloop.
 	Gtk.widgetShowAll window
 	Gtk.mainGUI
 
+-- | Copy the given surface to the exposed window on an expose event.
+onExpose :: IORef Cairo.Surface -> EventM.EventM EventM.EExpose Bool
+onExpose buffer = do
+	current_buffer <- liftIO $ readIORef buffer
+	dw <- EventM.eventWindow
+	-- Copy the buffer to the window
+	liftIO $ Gtk.renderWithDrawable dw $ do
+		Cairo.setSourceSurface current_buffer 0 0
+		Cairo.paint
+	return True -- No clue what this means
 
 {-
 runGUI s IS {..} = do
-- 
2.30.2