[HOpenGL] GLU.Tessellator crashes

[Jules Bean]

Balazs Komuves wrote:
> 
> Hello,
> 
> I can't reproduce this behaviour (though I didn't try very hard).
> Could you send some specific code which produces bus error on your setup?

Sure. Code attached below this message.

After some playing around minimalising this example, I have come to a 
stronger conclusion: the code only crashes when the Combiner callback 
gets invoked.

Since I have tolerance 0, that only happens if you have a duplicated 
vertex. If the vertex (200,200) appears twice (as in the simple example 
I attach) then you get the bus error, presumably when calling the Combiner.

This makes me suspect that the nasty peeking and poking going on in the 
AnnotatedVertex Storable instance is not quite right, or something else 
is wrong in withCombineCallback or combineProperties (see

http://hackage.haskell.org/packages/archive/OpenGL/2.2.1.1/doc/html/src/Graphics-Rendering-OpenGL-GLU-Tessellation.html

)

Code follows. I'd be interested to hear if it crashes for other people 
(could it be a bug in my OS's GLU?)

Jules

-- 

import Graphics.Rendering.OpenGL
import Graphics.UI.GLUT

import Control.Monad


main = do
   (progName,args) <-  getArgsAndInitialize
   initialDisplayMode $= [ DoubleBuffered, RGBAMode,
                           WithDepthBuffer]
   createWindow progName
   windowSize         $= (Size 640 480)

   blend              $= Enabled
   blendFunc          $= (SrcAlpha,OneMinusSrcAlpha)

   multisample $= Enabled
   --lineSmooth $= Enabled
   lineWidth $= 1
   reshapeCallback       $= Just reshape
   displayCallback $= display
   postRedisplay Nothing
   addTimerCallback 50 (idle)
   mainLoop

idle = do
   postRedisplay Nothing
   addTimerCallback 50 (idle)

display = do
   loadIdentity
   depthMask $= Enabled
   depthFunc $= Nothing -- Just Lequal
   clear [ColorBuffer,DepthBuffer]
   polygonMode $= (Line,Line)
   let pts = (figure8)
   -- let pts = (circle 27)
   pp <- tessRegion pts
   color $ Color4 1 1 0 (1::GLfloat)
   renderSimplePolygon pp

   swapBuffers

-- n-point approximation to a circle (does not cause crash whatever n
-- you use)
circle n =
   map (\t -> (200 + 200 * sin (t*2*pi),
               200 + 200 * cos (t*2*pi)))
   [0,1/n..1]

-- causes crash, presumably because of the duplicated point (200,200)
figure8 = 
[(200,0),(100,100),(200,200),(300,300),(200,400),(100,300),(200,200),(300,100)]
-- does not crash, as it has no duplicated point
figure8' = 
[(200,0),(100,100),(200,200),(300,300),(200,400),(100,300),(201,201),(300,100)]

-- 2D projection
reshape screenSize@(Size w h) = do
   viewport $= ((Position 0 0), screenSize)
   matrixMode $= Projection
   loadIdentity
   ortho2D 0 (fromIntegral w) 0 (fromIntegral h)
   matrixMode $= Modelview 0

-- this appears to give a bus error with sufficiently complex input
tessRegion :: [(GLfloat,GLfloat)] -> IO (SimplePolygon Int)
tessRegion pp =
   tessellate TessWindingOdd 0 (Normal3 0 0 0)
   (\vv (WeightedProperties (_,p) _ _ _) -> p) $
   ComplexPolygon
   [ComplexContour (map (\(x,y) -> AnnotatedVertex
                                   (Vertex3 (realToFrac x) (realToFrac 
y) 0)
                                   (0::Int))
                    pp)]

renderSimplePolygon (SimplePolygon pp) = mapM_ renderSimplePrimitive pp
renderSimplePrimitive (Primitive pm vv) =
   renderPrimitive pm . forM_ vv $ \(AnnotatedVertex v _) ->
   vertex v