ui/pointer: split AreaOp into RectAreaOp and EllipseAreaOp

Now that the pass through mode is moved into its own PassOp op,
it doesn't make sense to collect all area types into one exported
type.

Add RectAreaOp and EllipseAreaOp for clients; the internal
representation is still a single op. It can be changed later without
breaking clients.

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

ui/input/pointer.go

@@ -3,6 +3,9 @@
 package input
 
 import (
+	"encoding/binary"
+	"image"
+
 	"gioui.org/ui"
 	"gioui.org/ui/f32"
 	"gioui.org/ui/internal/ops"
@@ -41,12 +44,24 @@ type pointerHandler struct {
 	wantsGrab bool
 }
 
+type areaOp struct {
+	kind areaKind
+	size image.Point
+}
+
 type areaNode struct {
 	trans ui.Transform
 	next  int
-	area  pointer.AreaOp
+	area  areaOp
 }
 
+type areaKind uint8
+
+const (
+	areaRect areaKind = iota
+	areaEllipse
+)
+
 func (q *pointerQueue) collectHandlers(r *ui.OpsReader, events handlerEvents, t ui.Transform, area, node int, pass bool) {
 	for {
 		encOp, ok := r.Decode()
@@ -63,7 +78,7 @@ func (q *pointerQueue) collectHandlers(r *ui.OpsReader, events handlerEvents, t
 			op.Decode(encOp.Data)
 			pass = op.Pass
 		case ops.TypeArea:
-			var op pointer.AreaOp
+			var op areaOp
 			op.Decode(encOp.Data)
 			q.areas = append(q.areas, areaNode{trans: t, next: area, area: op})
 			area = len(q.areas) - 1
@@ -257,3 +272,44 @@ func (q *pointerQueue) Push(e pointer.Event, events handlerEvents) {
 		}
 	}
 }
+
+func (op *areaOp) Decode(d []byte) {
+	if ops.OpType(d[0]) != ops.TypeArea {
+		panic("invalid op")
+	}
+	bo := binary.LittleEndian
+	size := image.Point{
+		X: int(bo.Uint32(d[2:])),
+		Y: int(bo.Uint32(d[6:])),
+	}
+	*op = areaOp{
+		kind: areaKind(d[1]),
+		size: size,
+	}
+}
+
+func (op *areaOp) Hit(pos f32.Point) bool {
+	switch op.kind {
+	case areaRect:
+		if 0 <= pos.X && pos.X < float32(op.size.X) &&
+			0 <= pos.Y && pos.Y < float32(op.size.Y) {
+			return true
+		} else {
+			return false
+		}
+	case areaEllipse:
+		rx := float32(op.size.X) / 2
+		ry := float32(op.size.Y) / 2
+		rx2 := rx * rx
+		ry2 := ry * ry
+		xh := pos.X - rx
+		yk := pos.Y - ry
+		if xh*xh*ry2+yk*yk*rx2 <= rx2*ry2 {
+			return true
+		} else {
+			return false
+		}
+	default:
+		panic("invalid area kind")
+	}
+}