only drawing on available surface area

src/Affection/Draw.hs

@@ -12,6 +12,8 @@ module Affection.Draw
 
 import Affection.Types
 
+import Data.Maybe (maybe)
+
 import Foreign
 import Foreign.C.Types
 
@@ -75,18 +77,23 @@ handleDrawRequest
 handleDrawRequest pixels stride cpp dr@DrawRequest{..} = do
   ad <- get
   let surf = drawSurface ad
-  liftIO $ SDL.lockSurface surf
-  liftIO $ G.gegl_buffer_get
-    requestBuffer
-    (Just requestArea)
-    1
-    (Just $ drawFormat ad)
-    (pixels `plusPtr`
-      (rectangleX requestArea * cpp + rectangleY requestArea * stride))
-    stride
-    G.GeglAbyssNone
-  liftIO $ SDL.unlockSurface surf
-  -- liftIO $ SDL.updateWindowSurface $ drawWindow ad
+  mrealRect <- liftIO $ G.gegl_rectangle_intersect
+    requestArea
+    (G.GeglRectangle 0 0 (fst $ drawDimensions ad) (snd $ drawDimensions ad))
+  maybe (return()) (\realRect -> do
+    liftIO $ SDL.lockSurface surf
+    liftIO $ G.gegl_buffer_get
+      requestBuffer
+      (Just realRect)
+      1
+      (Just $ drawFormat ad)
+      (pixels `plusPtr`
+        (rectangleX realRect * cpp + rectangleY realRect * stride))
+      stride
+      G.GeglAbyssNone
+    liftIO $ SDL.unlockSurface surf
+    -- liftIO $ SDL.updateWindowSurface $ drawWindow ad
+    ) mrealRect
   case requestPersist of
     Yes ->
       return Nothing
@@ -103,19 +110,24 @@ invalidateDrawRequest
   -> Affection us ()
 invalidateDrawRequest pixels stride cpp dr@DrawRequest{..} = do
   ad <- get
-  let surf = drawSurface ad
-  liftIO $ clearArea requestBuffer requestArea
-  liftIO $ SDL.lockSurface surf
-  liftIO $ G.gegl_buffer_get
-    requestBuffer
-    (Just requestArea)
-    1
-    (Just $ drawFormat ad)
-    (pixels `plusPtr`
-      (rectangleX requestArea * cpp + rectangleY requestArea * stride))
-    stride
-    G.GeglAbyssNone
-  liftIO $ SDL.unlockSurface surf
+  mrealRect <- liftIO $ G.gegl_rectangle_intersect
+    requestArea
+    (G.GeglRectangle 0 0 (fst $ drawDimensions ad) (snd $ drawDimensions ad))
+  maybe (return()) (\realRect -> do
+    let surf = drawSurface ad
+    liftIO $ clearArea requestBuffer realRect
+    liftIO $ SDL.lockSurface surf
+    liftIO $ G.gegl_buffer_get
+      requestBuffer
+      (Just realRect)
+      1
+      (Just $ drawFormat ad)
+      (pixels `plusPtr`
+        (rectangleX realRect * cpp + rectangleY realRect * stride))
+      stride
+      G.GeglAbyssNone
+    liftIO $ SDL.unlockSurface surf
+    ) mrealRect
   case requestPersist of
     Kill (Just victim) ->
       liftIO $ G.gegl_node_drop victim