merge(#55)

image.go

@@ -4,6 +4,11 @@ type Image struct {
 	buffer []byte
 }
 
+// Creates a new image
+func NewImage(buf []byte) *Image {
+	return &Image{buf}
+}
+
 // Resize the image to fixed width and height
 func (i *Image) Resize(width, height int) ([]byte, error) {
 	options := Options{
@@ -190,8 +195,3 @@ func (i *Image) Size() (ImageSize, error) {
 func (i *Image) Image() []byte {
 	return i.buffer
 }
-
-// Creates a new image
-func NewImage(buf []byte) *Image {
-	return &Image{buf}
-}

image_test.go

@@ -246,6 +246,19 @@ func TestImageConvert(t *testing.T) {
 	Write("fixtures/test_image_convert_out.png", buf)
 }
 
+func TestTransparentImageConvert(t *testing.T) {
+	image := initImage("transparent.png")
+	options := Options{
+		Type:       JPEG,
+		Background: Color{255, 255, 255},
+	}
+	buf, err := image.Process(options)
+	if err != nil {
+		t.Errorf("Cannot process the image: %#v", err)
+	}
+	Write("fixtures/test_transparent_image_convert_out.jpg", buf)
+}
+
 func TestImageMetadata(t *testing.T) {
 	data, err := initImage("test.png").Metadata()
 	if err != nil {

options.go

@@ -80,6 +80,10 @@ type Color struct {
 	R, G, B uint8
 }
 
+// Shortcut to black RGB color representation
+var ColorBlack = Color{0, 0, 0}
+
+// Text-based watermark configuration
 type Watermark struct {
 	Width       int
 	DPI         int
@@ -96,6 +100,7 @@ type GaussianBlur struct {
 	MinAmpl float64
 }
 
+// Supported image transformation options
 type Options struct {
 	Height         int
 	Width          int
@@ -117,6 +122,7 @@ type Options struct {
 	NoProfile      bool
 	Interlace      bool
 	Rotate         Angle
+	Background     Color
 	Gravity        Gravity
 	Watermark      Watermark
 	Type           ImageType

resize.go

@@ -102,6 +102,12 @@ func Resize(buf []byte, o Options) ([]byte, error) {
 		return nil, err
 	}
 
+	// Flatten image on a background, if necessary
+	image, err = imageFlatten(image, imageType, o)
+	if err != nil {
+		return nil, err
+	}
+
 	saveOptions := vipsSaveOptions{
 		Quality:        o.Quality,
 		Type:           o.Type,
@@ -303,6 +309,15 @@ func watermakImage(image *C.VipsImage, w Watermark) (*C.VipsImage, error) {
 	return image, nil
 }
 
+func imageFlatten(image *C.VipsImage, imageType ImageType, o Options) (*C.VipsImage, error) {
+	// Only PNG images are supported for now
+	if imageType != PNG || o.Background == ColorBlack {
+		return image, nil
+	}
+
+	return vipsFlattenBackground(image, o.Background)
+}
+
 func zoomImage(image *C.VipsImage, zoom int) (*C.VipsImage, error) {
 	if zoom == 0 {
 		return image, nil

vips.go

@@ -252,6 +252,26 @@ func vipsInterpretation(image *C.VipsImage) Interpretation {
 	return Interpretation(C.vips_image_guess_interpretation_bridge(image))
 }
 
+func vipsFlattenBackground(image *C.VipsImage, background Color) (*C.VipsImage, error) {
+	var outImage *C.VipsImage
+
+	backgroundC := [3]C.double{
+		C.double(background.R),
+		C.double(background.G),
+		C.double(background.B),
+	}
+
+	err := C.vips_flatten_background_brigde(image, &outImage, (*C.double)(&backgroundC[0]))
+	if int(err) != 0 {
+		return nil, catchVipsError()
+	}
+
+	C.g_object_unref(C.gpointer(image))
+	image = outImage
+
+	return image, nil
+}
+
 func vipsPreSave(image *C.VipsImage, o *vipsSaveOptions) (*C.VipsImage, error) {
 	// Remove ICC profile metadata
 	if o.NoProfile {
@@ -267,8 +287,8 @@ func vipsPreSave(image *C.VipsImage, o *vipsSaveOptions) (*C.VipsImage, error) {
 	// Apply the proper colour space
 	var outImage *C.VipsImage
 	if vipsColourspaceIsSupported(image) {
-		err := int(C.vips_colourspace_bridge(image, &outImage, interpretation))
-		if err != 0 {
+		err := C.vips_colourspace_bridge(image, &outImage, interpretation)
+		if int(err) != 0 {
 			return nil, catchVipsError()
 		}
 		C.g_object_unref(C.gpointer(image))

vips.h

@@ -226,6 +226,15 @@ vips_webpsave_bridge(VipsImage *in, void **buf, size_t *len, int strip, int qual
 	);
 }
 
+int
+vips_flatten_background_brigde(VipsImage *in, VipsImage **out, double background[3]) {
+	VipsArrayDouble *vipsBackground = vips_array_double_new(background, 3);
+	return vips_flatten(in, out,
+		"background", vipsBackground,
+		NULL
+	);
+}
+
 int
 vips_init_image (void *buf, size_t len, int imageType, VipsImage **out) {
 	int code = 1;