all: make pointer.Area an interface

With an interface instead of anonymous functions, amending an
area's parameters can be done even after adding it to an OpHandler.

This will be useful when we switch to serialized op lists.

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

ui/gesture/gestures.go

@@ -37,6 +37,14 @@ type Scroll struct {
 	scroll float32
 }
 
+type Rect struct {
+	Size image.Point
+}
+
+type Ellipse struct {
+	Size image.Point
+}
+
 type flinger struct {
 	// Current offset in pixels.
 	x float32
@@ -254,30 +262,26 @@ func (f *flinger) Tick(now time.Time) int {
 	return idist
 }
 
-func Rect(sz image.Point) pointer.Area {
-	return func(pos f32.Point) pointer.HitResult {
-		if 0 <= pos.X && pos.X < float32(sz.X) &&
-			0 <= pos.Y && pos.Y < float32(sz.Y) {
-			return pointer.HitOpaque
-		} else {
-			return pointer.HitNone
-		}
+func (r *Rect) Hit(pos f32.Point) pointer.HitResult {
+	if 0 <= pos.X && pos.X < float32(r.Size.X) &&
+		0 <= pos.Y && pos.Y < float32(r.Size.Y) {
+		return pointer.HitOpaque
+	} else {
+		return pointer.HitNone
 	}
 }
 
-func Ellipse(sz image.Point) pointer.Area {
-	return func(pos f32.Point) pointer.HitResult {
-		rx := float32(sz.X) / 2
-		ry := float32(sz.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 pointer.HitOpaque
-		} else {
-			return pointer.HitNone
-		}
+func (e *Ellipse) Hit(pos f32.Point) pointer.HitResult {
+	rx := float32(e.Size.X) / 2
+	ry := float32(e.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 pointer.HitOpaque
+	} else {
+		return pointer.HitNone
 	}
 }