void addVert( int index, Vector2 position, Vector2 texCoord, Color col )
{
if( position == Vector2.Zero )
Debug.break_();
_vertices.ensureCapacity();
_vertices.buffer[index].Position = position.toVector3();
_vertices.buffer[index].TextureCoordinate = texCoord;
_vertices.buffer[index].Color = col;
_vertices.length++;
}