feat(#3, #5): support image operations

options.go

@@ -1,5 +1,11 @@
 package bimg
 
+/*
+#cgo pkg-config: vips
+#include "vips/vips.h"
+*/
+import "C"
+
 const QUALITY = 80
 
 type Gravity int
@@ -16,6 +22,26 @@ func (i Interpolator) String() string {
 	return interpolations[i]
 }
 
+type Rotation struct {
+	angle int
+}
+
+func (a Rotation) calculate() int {
+	angle := a.angle
+	divisor := angle % 90
+	if divisor != 0 {
+		angle = a.angle - divisor
+	}
+	return angle
+}
+
+type Direction int
+
+const (
+	HORIZONTAL Direction = C.VIPS_DIRECTION_HORIZONTAL
+	VERTICAL   Direction = C.VIPS_DIRECTION_VERTICAL
+)
+
 type Options struct {
 	Height       int
 	Width        int
@@ -23,7 +49,9 @@ type Options struct {
 	Enlarge      bool
 	Extend       int
 	Embed        bool
-	Interpolator Interpolator
-	Gravity      Gravity
 	Quality      int
+	Rotate       int
+	Flip         Direction
+	Gravity      Gravity
+	Interpolator Interpolator
 }