op: introduce CallOp

We'd like to improve the API of Flex, Stack and similar layouts
that use MacroOps internall. Unfortunately, the

  func (m MacroOp) Add(o *Ops)

method causes the MacroOp to be allocated on the heap, ruining the
nice garbage-free property of layouts.

Fortunately, layouts don't need the feature that caused the heap
allocation: invoking operation lists different than the current.

CallOp separates the invoke-different-list semantic from MacroOp,
in preparation for removing the feature from MacroOp.

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

internal/opconst/ops.go

@@ -26,6 +26,7 @@ const (
 	TypeAux
 	TypeClip
 	TypeProfile
+	TypeCall
 )
 
 const (
@@ -47,6 +48,7 @@ const (
 	TypeAuxLen          = 1
 	TypeClipLen         = 1 + 4*4
 	TypeProfileLen      = 1
+	TypeCallLen         = 1
 )
 
 func (t OpType) Size() int {
@@ -69,12 +71,13 @@ func (t OpType) Size() int {
 		TypeAuxLen,
 		TypeClipLen,
 		TypeProfileLen,
+		TypeCallLen,
 	}[t-firstOpIndex]
 }
 
 func (t OpType) NumRefs() int {
 	switch t {
-	case TypeMacro, TypeKeyInput, TypePointerInput, TypeProfile:
+	case TypeMacro, TypeKeyInput, TypePointerInput, TypeProfile, TypeCall:
 		return 1
 	case TypeImage:
 		return 2

internal/ops/reader.go

@@ -38,6 +38,11 @@ type macroOp struct {
 	pc      pc
 }
 
+// Shadow of op.CallOp.
+type callOp struct {
+	ops *op.Ops
+}
+
 type pc struct {
 	data int
 	refs int
@@ -94,6 +99,24 @@ func (r *Reader) Decode() (EncodedOp, bool) {
 			block := r.stack[len(r.stack)-1]
 			n += block.endPC.data - r.pc.data - opconst.TypeAuxLen
 			data = data[:n]
+		case opconst.TypeCall:
+			var op callOp
+			op.decode(data, refs)
+			endPC := pc{
+				data: len(op.ops.Data()),
+				refs: len(op.ops.Refs()),
+			}
+			retPC := r.pc
+			retPC.data += n
+			retPC.refs += nrefs
+			r.stack = append(r.stack, macro{
+				ops:   r.ops,
+				retPC: retPC,
+				endPC: endPC,
+			})
+			r.pc = pc{}
+			r.ops = op.ops
+			continue
 		case opconst.TypeMacro:
 			var op macroOp
 			op.decode(data, refs)
@@ -148,6 +171,15 @@ func (op *opMacroDef) decode(data []byte) {
 	}
 }
 
+func (m *callOp) decode(data []byte, refs []interface{}) {
+	if opconst.OpType(data[0]) != opconst.TypeCall {
+		panic("invalid op")
+	}
+	*m = callOp{
+		ops: refs[0].(*op.Ops),
+	}
+}
+
 func (m *macroOp) decode(data []byte, refs []interface{}) {
 	if opconst.OpType(data[0]) != opconst.TypeMacro {
 		panic("invalid op")

op/op.go

@@ -45,6 +45,12 @@ The StackOp saves the current state to the state stack and restores it later:
 	// Restore the previous transform.
 	stack.Pop()
 
+The CallOp invokes another operation list:
+
+	ops := new(op.Ops)
+	ops2 := new(op.Ops)
+	op.CallOp{Ops: ops2}.Add(ops)
+
 The MacroOp records a list of operations to be executed later:
 
 	ops := new(op.Ops)
@@ -105,6 +111,13 @@ type MacroOp struct {
 	pc        pc
 }
 
+// CallOp invokes all the operations from a separate
+// operations list.
+type CallOp struct {
+	// Ops is the list of operations to invoke.
+	Ops *Ops
+}
+
 // InvalidateOp requests a redraw at the given time. Use
 // the zero value to request an immediate redraw.
 type InvalidateOp struct {
@@ -134,6 +147,15 @@ type pc struct {
 	refs int
 }
 
+// Add the call to the operation list.
+func (c CallOp) Add(o *Ops) {
+	if c.Ops == nil {
+		return
+	}
+	data := o.Write(opconst.TypeCallLen, c.Ops)
+	data[0] = byte(opconst.TypeCall)
+}
+
 // Push (save) the current operations state.
 func (s *StackOp) Push(o *Ops) {
 	if s.active {