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/internal/ops/ops.go

@@ -2,8 +2,11 @@ package ops
 
 type OpType byte
 
+// Start at a high number for easier debugging.
+const FirstOpIndex = 200
+
 const (
-	TypeBlockDef OpType = iota
+	TypeBlockDef OpType = iota + FirstOpIndex
 	TypeBlock
 	TypeTransform
 	TypeLayer
@@ -20,18 +23,33 @@ const (
 )
 
 const (
-	TypeBlockDefLen       = 1 + 4
-	TypeBlockLen          = 1 + 4
+	TypeBlockDefLen       = 1 + 4 + 4
+	TypeBlockLen          = 1 + 4 + 4
 	TypeTransformLen      = 1 + 4*2
 	TypeLayerLen          = 1
 	TypeRedrawLen         = 1 + 8
-	TypeClipLen           = 1 + 4
-	TypeImageLen          = 1 + 4 + 4*4
+	TypeClipLen           = 1
+	TypeImageLen          = 1 + 4*4
 	TypeDrawLen           = 1 + 4*4
 	TypeColorLen          = 1 + 4
-	TypePointerHandlerLen = 1 + 4 + 4 + 1
-	TypeKeyHandlerLen     = 1 + 4 + 1
+	TypePointerHandlerLen = 1 + 1
+	TypeKeyHandlerLen     = 1 + 1
 	TypeHideInputLen      = 1
 	TypePushLen           = 1
 	TypePopLen            = 1
+
+	TypeBlockDefRefs       = 0
+	TypeBlockRefs          = 0
+	TypeTransformRefs      = 0
+	TypeLayerRefs          = 0
+	TypeRedrawRefs         = 0
+	TypeClipRefs           = 1
+	TypeImageRefs          = 1
+	TypeDrawRefs           = 0
+	TypeColorRefs          = 0
+	TypePointerHandlerRefs = 2
+	TypeKeyHandlerRefs     = 1
+	TypeHideInputRefs      = 0
+	TypePushRefs           = 0
+	TypePopRefs            = 0
 )