i have changed the red parts of tutorial 2
it should make a square but it makes a triangle
whats wrong?

function TForm1.InitVertexBuffer(): boolean;

var _vb : array[0...3] of TCustomVertex;
_ptr : pByte;

begin
Result := false;

// Initialize the vertices.
_vb[0] := GetCustomVertex(0, 0, 0.5, 1, $FFFF0000);
_vb[1] := GetCustomVertex(250, 0, 0.5, 1, $FF00FF00);
_vb[2] := GetCustomVertex( 0, 250, 0.5, 1, $FF0000FF);
_vb[3] := GetCustomVertex(250, 250, 0.5, 1, $FF0000FF);



// Create a vertex buffer.
if failed(PowerGraph.D3DDevice8.CreateVertexBuffer(Si zeOf(_vb), 0,
D3DFVF_CUSTOMVERTEX,
D3DPOOL_DEFAULT,
VertexBuffer)) then exit;

// Lock, fill and unlock vertex buffer.
if failed(VertexBuffer.Lock(0, SizeOf(_vb), _ptr, 0)) then exit;
Move(_vb, _ptr^, SizeOf(_vb));
VertexBuffer.Unlock;

// All right
Result := true;
end;