account_invoice_view.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>
        <record id="invoice_supplier_form_ext" model="ir.ui.view">
            <field name="name">invoice.supplier.form.ext</field>
            <field name="model">account.invoice</field>
            <field name="inherit_id" ref="account.invoice_supplier_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='currency_id']" position="after">
					<field name="ref_purchase_id" options="{'limit': 10, 'create': false, 'create_edit': false}"/> 
                    <field name="ref_order_id" options="{'limit': 10, 'create': false, 'create_edit': false}" attrs="{'invisible': ['|',('ref_order_id','=',False),('cost_order_id','!=',False)]}"/>
                    <field name="cost_order_id" options="{'limit': 10, 'create': false, 'create_edit': false}" attrs="{'invisible': [('ref_order_id','!=',False)]}"/>
					<field name="ref_project_name"/>
                </xpath>
            </field>
        </record>
	</data>
</openerp>