all: [API] change op.Offset to take integer coordinates

op.Offset is a convenience function most often used by layouts. Layouts
usually operate in integer coordinates, and the float32 version of op.Offset
needlessly force conversions from int to float32. This change makes op.Offset
take integer coordinates, to better match its intended use.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/dnd.go

@@ -64,7 +64,7 @@ func (d *Draggable) Layout(gtx layout.Context, w, drag layout.Widget) layout.Dim
 
 	if drag != nil && d.drag.Pressed() {
 		rec := op.Record(gtx.Ops)
-		op.Offset(pos).Add(gtx.Ops)
+		op.Offset(pos.Round()).Add(gtx.Ops)
 		drag(gtx)
 		op.Defer(gtx.Ops, rec.Stop())
 	}