sale_discount_total/views/sale_view.xml

<?xml version="1.0" encoding="UTF-8"?>
<openerp>
    <data>

        <record id="discount_view_orer_line_form" model="ir.ui.view">
            <field name="name">discount.sale.order.line.form</field>
            <field name="model">sale.order.line</field>
            <field name="inherit_id" ref="sale.view_order_line_form2"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='discount']" position="attributes">
                    <attribute name="digits">(16, 2)</attribute>
                </xpath>
            </field>
        </record>

        <record id="discount_sale_view_form" model="ir.ui.view">
            <field name="name">discount.sale.order.form</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//tree/field[@name='discount']" position="attributes">
                    <attribute name="digits">(16, 2)</attribute>
                </xpath>

                <xpath expr="//tree[@string='Sales Order Lines']//field[@name='discount']" position="after">
                    <field name="discount_amount" readonly="1"/>
                </xpath>

                <xpath expr="//group[@name='sale_total']" position="replace">
                    <group col="4">
                        <group name="discount" colspan="2">
                            <field name="discount_type"/>
                            <field name="discount_rate"/>
                        </group>
                        <group class="oe_subtotal_footer oe_right" colspan="2" name="sale_total">
                            <field name="amount_untaxed" widget='monetary' options="{'currency_field': 'currency_id'}"/>
                            <field name="amount_discount" widget='monetary' options="{'currency_field': 'currency_id'}"/>
                            <field name="amount_tax" widget='monetary' options="{'currency_field': 'currency_id'}"/>
                            <div class="oe_subtotal_footer_separator oe_inline">
                                <label for="amount_total" />
                                <button name="button_dummy"
                                        states="draft,sent" string="(update)" type="object" class="oe_edit_only oe_link"/>
                            </div>
                            <field name="amount_total" nolabel="1" class="oe_subtotal_footer_separator" widget='monetary' options="{'currency_field': 'currency_id'}"/>
                        </group>
                    </group>
                </xpath>
                <xpath expr="//button[@string='Create Invoice']" position="attributes">
                    <attribute name="context">{'discount_type':discount_type,'discount_rate':discount_rate,'amount_discount':amount_discount}</attribute>
                </xpath>
            </field>
        </record>
    </data>
</openerp>