What is the dashboard graph widget can used for on the qweb template, like project overview timesheet plan from sale_timesheet module or etc. ?

I try this but widget does not work

<div class="row">

     <t t-name="MyGraph">

         <t-esc="graph_data" t-options="{'widget': 'dashboard_graph' }" t-attf-graph_type="'line'"/>

     </t>

</div>

Why the widget can not rendered on the qweb ?