OpenGL command crashing under Lazarus but not Dephi 5

[paul_nicholls]

Hi all, I use the ScreenToWorld method (below) like so:

Method using code

Begin
{...}
        p0 := ScreenToWorld(FMousePosX,FMousePosY,0);
        p1 := ScreenToWorld(FMousePosX,FMousePosY,1);
{...}
End;

Method being used

Function  TAbaloneGL.ScreenToWorld(AScreenX, AScreenY, AScreenZ : GLdouble) : TVector3f;
Var
    Viewport : TViewPortArray;
    MVMat    : T16dArray;
    PJMat    : T16dArray;
    ObjX     : GLdouble;
    ObjY     : GLdouble;
    ObjZ     : GLdouble;
Begin
    // Retrieves the viewport
    glGetIntegerv(GL_VIEWPORT, @Viewport);
    // Retrieve the matrices
    glGetDoublev(GL_MODELVIEW_MATRIX, @MVMat[0]);
    glGetDoublev(GL_PROJECTION_MATRIX, @PJMat[0]);
    
    // Unproject screen coordinates
    gluUnProject(
        AScreenX,
        Viewport[3] - AScreenY,
        AScreenZ,
        MVMat, PJMat, Viewport,
        @ObjX, @ObjY, @ObjZ);
        
    Result := V3(ObjX, ObjY, ObjZ);
End;

This works just find under Delphi 5 without any issues, but when I compile and run it using Lazarus (latest version 0.9.1, it crashes on the gluUnProject line with an access violation

If I run it through the debugger it gives this error:

"Project raised exception class 'External: SIGSEGV"

I can't seem to figure it out...

PS I am using the GL.pas and GLU.pas files that come with JEDI-SDL if that helps...

cheers,
Paul.