op: change Defer to only restore transformation state

It turns out restoring all operation state from the moment Defer
is executed is too much; for example, a right-click pop-up needs
the transformation, but not the current clip.

Change Defer to only restore the transformation, and reset all
other state.

Other combinations may be needed in future; we'll deal with them then,
possibly by exposing the load state mask.

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

internal/opconst/ops.go

@@ -57,7 +57,7 @@ const (
 	TypeKeyFocusLen        = 1 + 1
 	TypeKeySoftKeyboardLen = 1 + 1
 	TypeSaveLen            = 1 + 4
-	TypeLoadLen            = 1 + 4
+	TypeLoadLen            = 1 + 1 + 4
 	TypeAuxLen             = 1
 	TypeClipLen            = 1 + 4*4 + 1
 	TypeProfileLen         = 1
@@ -67,6 +67,20 @@ const (
 	TypeDashLen            = 1 + 4 + 1
 )
 
+// StateMask is a bitmask of state types a load operation
+// should restore.
+type StateMask uint8
+
+const (
+	TransformState StateMask = 1 << iota
+
+	AllState = ^StateMask(0)
+)
+
+// InitialStateID is the ID for saving and loading
+// the initial operation state.
+const InitialStateID = 0
+
 func (t OpType) Size() int {
 	return [...]int{
 		TypeMacroLen,

internal/ops/ops.go

@@ -72,11 +72,11 @@ func DecodeSave(data []byte) int {
 	return int(bo.Uint32(data[1:]))
 }
 
-// DecodeLoad decodes the state id of a restore op.
-func DecodeLoad(data []byte) int {
+// DecodeLoad decodes the state id and mask of a load op.
+func DecodeLoad(data []byte) (int, opconst.StateMask) {
 	if opconst.OpType(data[0]) != opconst.TypeLoad {
 		panic("invalid op")
 	}
 	bo := binary.LittleEndian
-	return int(bo.Uint32(data[1:]))
+	return int(bo.Uint32(data[2:])), opconst.StateMask(data[1])
 }

internal/rendertest/render_test.go

@@ -107,13 +107,17 @@ func TestDeferredPaint(t *testing.T) {
 	run(t, func(o *op.Ops) {
 		state := op.Save(o)
 		clip.Rect(image.Rect(0, 0, 80, 80)).Op().Add(o)
-		paint.ColorOp{Color: color.NRGBA{A: 0xff, R: 0xff}}.Add(o)
+		paint.ColorOp{Color: color.NRGBA{A: 0xff, G: 0xff}}.Add(o)
+		paint.PaintOp{}.Add(o)
+
+		op.Affine(f32.Affine2D{}.Offset(f32.Pt(20, 20))).Add(o)
 		m := op.Record(o)
+		clip.Rect(image.Rect(0, 0, 80, 80)).Op().Add(o)
+		paint.ColorOp{Color: color.NRGBA{A: 0xff, R: 0xff, G: 0xff}}.Add(o)
 		paint.PaintOp{}.Add(o)
 		paintMacro := m.Stop()
 		op.Defer(o, paintMacro)
-		paint.ColorOp{Color: color.NRGBA{A: 0xff, G: 0xff}}.Add(o)
-		paint.PaintOp{}.Add(o)
+
 		state.Load()
 		op.Affine(f32.Affine2D{}.Offset(f32.Pt(10, 10))).Add(o)
 		clip.Rect(image.Rect(0, 0, 80, 80)).Op().Add(o)