Camera OnPostRenderer on iPhone/iPad sometimes paints all the GL.Lines Black.

Hi I am using the following code to render a number of marks without inducing too much rendering overhead. It takes only one draw call. It works fine in the editor but at certain camera angles/positions on the iphone and ipad the drawn lines are drawn black instead of the desired colour.

var drawLines = true; private var lineMaterial : Material; private var stateLink : StateController;

function Awake () { lineMaterial = new Material( "Shader \"Lines/Colored Blended\" {" + "SubShader { Tags { \"Queue\" = \"Transparent+2\" \"RenderType\"=\"Transparent\"}" + "Pass {" + " BindChannels { Bind \"Color\",color }" + " Blend SrcAlpha OneMinusSrcAlpha" + " ZWrite Off Cull Off Fog { Mode Off }" + "} } }"); lineMaterial.hideFlags = HideFlags.HideAndDontSave; lineMaterial.shader.hideFlags = HideFlags.HideAndDontSave; stateLink = GameObject.FindWithTag ("Engine").GetComponent(StateController); }

function OnPostRender () { if(drawLines) { lineMaterial.SetPass(0); GL.Begin(GL.LINES); stateLink.drawTrajMarks(); GL.End(); } }

function OnApplicationQuit () { DestroyImmediate(lineMaterial); }

@script RequireComponent(Camera)

The line stateLink.drawTrajMarks(); calls functions which draw lines by calling positions from an number of different objects.

eg.

function drawTrajMarks()
{
    ...
    GL.Color(colour);
    for (var q = 0; q < circle2.length-1; q++)
    {
        GL.Vertex(circle2[q]+posnPnt );
        GL.Vertex(circle2[q+1]+posnPnt );
    }
...
}

I have tried a number of things to determine why the color goes black only at certain camera angles. I thought initially it was a z buffer order problem. But even if I change to ZTest always, at some camera angles the lines become black. I would be very interested in any pointers of where I should look next.