OpenGL VBO's in Haskell

Question

Basing on this post, I was trying to figure out how to use VBO's in Haskell. I tried to fill in the bits that were not covered there:

data Sprite = Sprite { spriteImage :: Image
                     , spritePosition :: Position
                     } deriving (Show, Eq)

spriteBatch :: [Sprite] -> [(TextureObject, [Sprite])]
spriteBatch = (map f) . toList . (groupedBy (imageTexture . spriteImage))
    where f (t, s) = (t, s)

offset = plusPtr nullPtr

renderSprites :: [Sprite] -> IO ()
renderSprites l = (flip mapM_) (spriteBatch l) $ \(t, sps) -> do
        textureBinding Texture2D $= Just t
        let l = concat $ map sprToList sps
        vbo <- vboOfList ((length l)*4) l
        displayVbo vbo $ fromIntegral $ length sps
    where
        sprToList :: Sprite -> [GLfloat]
        sprToList (Sprite (Image _ (TexCoord2 u0 v0) (TexCoord2 u1 v1) (Size w h) _) (Position x y)) = 
            [fromIntegral x, fromIntegral y, u0, v0
            ,fromIntegral (x+w), fromIntegral y, u1, v0
            ,fromIntegral (x+w), fromIntegral (y+h), u1, v1
            ,fromIntegral x, fromIntegral (y+h), u0, v1
            ]

vboOfList :: Int -> [GLfloat] -> IO BufferObject
vboOfList size elems = do
    let ptrsize = toEnum $ size * 4
        arrayType = ElementArrayBuffer
    (array:_) <- genObjectNames 1
    bindBuffer arrayType $= Just array
    arr <- newListArray (0, size - 1) elems
    withStorableArray arr $ \ptr -> bufferData arrayType $= (ptrsize, ptr, StaticDraw)
    bindBuffer ArrayBuffer $= Nothing
    return array

displayVbo buff size = do
    let stride = 2*(2*4)
        vxDesc = VertexArrayDescriptor 2 Float stride $ offset 0
        texCoo = VertexArrayDescriptor 2 Float stride $ offset 8
    bindBuffer ArrayBuffer $= Just buff

    arrayPointer VertexArray $= vxDesc
    arrayPointer TextureCoordArray $= texCoo

    clientState VertexArray $= Enabled
    clientState TextureCoordArray $= Enabled

    drawArrays Quads 0 size
    bindBuffer ArrayBuffer $= Nothing

You can find the full code here, in case you need to.

On the master branch, the very same function uses normal vertex calls to draw the Sprites and it works perfectly. But using VBO's, the sprite just isn't there; I get a blank screen.

Can anyone explain to me what I did wrong here?

Answer 1

You're using one buffer for vertices and uvs. Use two buffers, one for vertices and one for uvs.