we can haz GUI?

we can.

src/UI/Callbacks.hs

@@ -6,6 +6,14 @@ import Control.Monad.Trans (liftIO)
 import Types
 import UI.UITypes
 
+import qualified Graphics.Rendering.OpenGL.GL         as GL
+import           Control.Lens                         ((^.), (.~), (%~))
+import           Render.Misc                          (genColorData)
+import           Foreign.Marshal.Array (pokeArray)
+import           Foreign.Marshal.Alloc (allocaBytes)
+import           Control.Monad.RWS.Strict             (get, liftIO, modify)
+
+
 data Pixel = Pixel Int Int
 
 getGUI :: [GUIAny]
@@ -47,12 +55,48 @@ alternateClickHandler :: Pixel -> Pioneers ()
 alternateClickHandler (Pixel x y) = liftIO $ putStrLn $ unwords ["alternate press on (",show x,",",show y,")"]
 
 
--- | informs the GUI to prepare a blitting of state ^. gl.hudTexture
+-- | informs the GUI to prepare a blitting of state ^. gl.glHud.hudTexture
 --
 --TODO: should be done asynchronously at one point.
+--        -> can't. if 2 Threads bind Textures its not sure
+--           on which one the GPU will work.
+--           "GL.textureBinding GL.Texture2D" is a State set
+--           to the texture all following works on.
+--
+--           https://www.opengl.org/wiki/GLAPI/glTexSubImage2D for copy
 prepareGUI :: Pioneers ()
 prepareGUI = do
-                return ()
+                state <- get
+                let tex = (state ^. gl.glHud.hudTexture)
+                liftIO $ do
+                    -- bind texture - all later calls work on this one.
+                    GL.textureBinding GL.Texture2D GL.$= Just tex
+                    mapM_ (copyGUI tex) getGUI
+                modify $ ui.uiHasChanged .~ False
+
+--TODO: Perform border-checking ... is xoff + width and yoff+height inside the screen-coordinates..
+copyGUI :: GL.TextureObject -> GUIAny -> IO ()
+copyGUI tex widget = do
+                        let (xoff, yoff, width, height) = getBoundary widget
+                            int = fromInteger.toInteger --conversion between Int8, GLInt, Int, ...
+                            --temporary color here. lateron better some getData-function to
+                            --get a list of pixel-data or a texture.
+                            color = case widget of
+                                (GUIAnyC _)   -> [255,0,0,128]
+                                (GUIAnyB _ _) -> [255,255,0,255]
+                                (GUIAnyP _)   -> [128,128,128,255]
+                                _             -> [255,0,255,255]
+                        allocaBytes (width*height*4) $ \ptr -> do
+                                --copy data into C-Array
+                                pokeArray ptr (genColorData (width*height) color)
+                                GL.texSubImage2D
+                                        GL.Texture2D
+                                        0
+                                        (GL.TexturePosition2D (int xoff) (int yoff))
+                                        (GL.TextureSize2D (int width) (int height))
+                                        (GL.PixelData GL.RGBA GL.UnsignedByte ptr)
+                        mapM_ (copyGUI tex) (getChildren widget)
+copyGUI _ _ = return ()
 
 --TODO: Add scroll-Handler, return (Pioneers Bool) to indicate event-bubbling etc.
 --TODO: Maybe queues are better?