Added Inset and Add method to RectangleF

rectanglef.go

@@ -1,6 +1,7 @@
 package geom
 
 // RectangleF is defined by two points, the minimum and maximum (floating point).
+// Tries to use the same interface as the image.Rectangle but uses float64 instead of int.
 type RectangleF struct {
 	Min, Max PointF
 }
@@ -16,6 +17,34 @@ func RectF(x0, y0, x1, y1 float64) RectangleF {
 	return RectangleF{PtF(x0, y0), PtF(x1, y1)}
 }
 
+// Add translates rectangle r by point p.
+func (r RectangleF) Add(p PointF) RectangleF {
+	return RectangleF{
+		PointF{r.Min.X + p.X, r.Min.Y + p.Y},
+		PointF{r.Max.X + p.X, r.Max.Y + p.Y},
+	}
+}
+
+// Inset returns the rectangle r inset by n. The resulting rectangle will never have
+// a negative size.
+func (r RectangleF) Inset(n float64) RectangleF {
+	if r.Dx() < 2*n {
+		r.Min.X = (r.Min.X + r.Max.X) / 2
+		r.Max.X = r.Min.X
+	} else {
+		r.Min.X += n
+		r.Max.X -= n
+	}
+	if r.Dy() < 2*n {
+		r.Min.Y = (r.Min.Y + r.Max.Y) / 2
+		r.Max.Y = r.Min.Y
+	} else {
+		r.Min.Y += n
+		r.Max.Y -= n
+	}
+	return r
+}
+
 // Dx returns the width of r.
 func (r RectangleF) Dx() float64 {
 	return r.Max.X - r.Min.X