add support for image rotation

data/data.go

@@ -32,6 +32,9 @@ type Options struct {
 	// If true, resize the image to fit in the specified dimensions.  Image
 	// will not be cropped, and aspect ratio will be maintained.
 	Fit bool
+
+	// Rotate image the specified degrees counter-clockwise.  Valid values are 90, 180, 270.
+	Rotate int
 }
 
 func (o Options) String() string {
@@ -63,6 +66,11 @@ func ParseOptions(str string) *Options {
 	for _, part := range parts[1:] {
 		if part == "fit" {
 			o.Fit = true
+			continue
+		}
+		if len(part) > 2 && strings.HasPrefix(part, "r=") {
+			o.Rotate, _ = strconv.Atoi(part[2:])
+			continue
 		}
 	}
 

readme.md

@@ -59,6 +59,12 @@ always, the original aspect ratio will be preserved. Specifying the `fit`
 option with only one of either width or height does the same thing as if `fit`
 had not been specified.
 
+#### Rotate ####
+
+The `r={degrees}` option will rotate the image the specified number of degrees,
+counter-clockwise.  Valid degrees values are `90`, `180`, and `270`.  Images
+are rotated **after** being resized.
+
 ### Remote URL ###
 
 The URL of the original image to load is specified as the remainder of the
@@ -85,6 +91,7 @@ x100    | 100px tall, proportional width           | ![x100](https://s.wjn.me/x1
 100x150 | 100 by 150 pixels, cropping as needed    | ![100x150](https://s.wjn.me/100x150/https://willnorris.com/content/uploads/2013/12/small-things.jpg)
 100     | 100px square, cropping as needed         | ![100](https://s.wjn.me/100/https://willnorris.com/content/uploads/2013/12/small-things.jpg)
 150,fit | fit to be no more than 150 by 150 pixels | ![150,fit](https://s.wjn.me/150,fit/https://willnorris.com/content/uploads/2013/12/small-things.jpg)
+100,r=90| 100px square, rotated 90 degrees         | ![100,r=90](https://s.wjn.me/100,r=90/https://willnorris.com/content/uploads/2013/12/small-things.jpg)
 
 
 ## License ##

transform/transform.go

@@ -49,6 +49,7 @@ func Transform(img data.Image, opt *data.Options) (*data.Image, error) {
 		return nil, err
 	}
 
+	// convert percentage width and height values to absolute values
 	var h, w int
 	if opt.Width > 0 && opt.Width < 1 {
 		w = int(float64(m.Bounds().Max.X-m.Bounds().Min.X) * opt.Width)
@@ -72,6 +73,19 @@ func Transform(img data.Image, opt *data.Options) (*data.Image, error) {
 		}
 	}
 
+	// rotate
+	switch opt.Rotate {
+	case 90:
+		m = imaging.Rotate90(m)
+		break
+	case 180:
+		m = imaging.Rotate180(m)
+		break
+	case 270:
+		m = imaging.Rotate270(m)
+		break
+	}
+
 	// encode image
 	buf := new(bytes.Buffer)
 	switch format {