Added progressive jpeg functionality.

README.md

@@ -39,6 +39,7 @@ The [install script](https://github.com/lovell/sharp/blob/master/preinstall.sh)
 - Enlarge
 - Crop
 - Rotate (with auto-rotate based on EXIF orientation)
+- Progressive
 - Flip (with auto-flip based on EXIF metadata)
 - Flop
 - Zoom
@@ -159,6 +160,7 @@ options := bimg.Options{
   Crop:         true,
   Quality:      95,
   Rotate:       180,
+  Interlace:    1,
 }
 
 buffer, err := bimg.Read("image.jpg")
@@ -618,6 +620,7 @@ type Options struct {
   Flip         bool
   Flop         bool
   NoAutoRotate bool
+  Interlace    int
   Rotate       Angle
   Gravity      Gravity
   Watermark    Watermark

options.go

@@ -88,6 +88,7 @@ type Options struct {
 	Flip         bool
 	Flop         bool
 	NoAutoRotate bool
+	Interlace    int
 	Rotate       Angle
 	Gravity      Gravity
 	Watermark    Watermark

resize.go

@@ -126,6 +126,7 @@ func Resize(buf []byte, o Options) ([]byte, error) {
 		Quality:     o.Quality,
 		Type:        o.Type,
 		Compression: o.Compression,
+		Interlace:   o.Interlace,
 	}
 
 	// Finally save as buffer

vips.go

@@ -35,6 +35,7 @@ type vipsSaveOptions struct {
 	Quality     int
 	Compression int
 	Type        ImageType
+	Interlace   int
 }
 
 type vipsWatermarkOptions struct {
@@ -235,7 +236,7 @@ func vipsSave(image *C.struct__VipsImage, o vipsSaveOptions) ([]byte, error) {
 		break
 	default:
 		debug("Save JPEG options: Q: %s", o.Quality)
-		err = C.vips_jpegsave_bridge(image, &ptr, &length, 1, C.int(o.Quality), 0)
+		err = C.vips_jpegsave_bridge(image, &ptr, &length, 1, C.int(o.Quality), C.int(o.Interlace))
 		break
 	}
 

vips_test.go

@@ -30,7 +30,7 @@ func TestVipsRead(t *testing.T) {
 
 func TestVipsSave(t *testing.T) {
 	image, _, _ := vipsRead(readImage("test.jpg"))
-	options := vipsSaveOptions{Quality: 95, Type: JPEG}
+	options := vipsSaveOptions{Quality: 95, Type: JPEG, Interlace: 1}
 
 	buf, err := vipsSave(image, options)
 	if err != nil {