ui: let OpsReader keep track of references

Instead of exposing the entire reference slice, return the relevant
references from Next.

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

ui/pointer/pointer.go

@@ -3,7 +3,6 @@
 package pointer
 
 import (
-	"encoding/binary"
 	"time"
 
 	"gioui.org/ui"
@@ -72,26 +71,20 @@ const (
 func (h OpHandler) Add(o *ui.Ops) {
 	data := make([]byte, ops.TypePointerHandlerLen)
 	data[0] = byte(ops.TypePointerHandler)
-	bo := binary.LittleEndian
 	if h.Grab {
 		data[1] = 1
 	}
-	bo.PutUint32(data[2:], uint32(o.Ref(h.Key)))
-	bo.PutUint32(data[6:], uint32(o.Ref(h.Area)))
-	o.Write(data)
+	o.Write(data, []interface{}{h.Key, h.Area})
 }
 
 func (h *OpHandler) Decode(d []byte, refs []interface{}) {
-	bo := binary.LittleEndian
 	if ops.OpType(d[0]) != ops.TypePointerHandler {
 		panic("invalid op")
 	}
-	key := int(bo.Uint32(d[2:]))
-	area := int(bo.Uint32(d[6:]))
 	*h = OpHandler{
 		Grab: d[1] != 0,
-		Key:  refs[key].(Key),
-		Area: refs[area].(Area),
+		Key:  refs[0].(Key),
+		Area: refs[1].(Area),
 	}
 }