Animated GIF support for ExtractArea

vips/conversion.c

@@ -39,6 +39,35 @@ int extract_image_area(VipsImage *in, VipsImage **out, int left, int top,
   return vips_extract_area(in, out, left, top, width, height, NULL);
 }
 
+int extract_area_multi_page(VipsImage *in, VipsImage **out, int left, int top, int width, int height) {
+  VipsObject *base = VIPS_OBJECT(vips_image_new());
+  int page_height = vips_image_get_page_height(in);
+  int n_pages = in->Ysize / page_height;
+
+  VipsImage **page = (VipsImage **) vips_object_local_array(base, n_pages);
+  VipsImage **copy = (VipsImage **) vips_object_local_array(base, 1);
+
+  // split image into cropped frames
+  for (int i = 0; i < n_pages; i++) {
+    if(vips_extract_area(in, &page[i], left, page_height * i + top, width, height, NULL)) {
+      g_object_unref(base);
+      return -1;
+    }
+  }
+  // reassemble frames and set page height
+  // copy before modifying metadata
+  if(
+    vips_arrayjoin(page, &copy[0], n_pages, "across", 1, NULL) ||
+    vips_copy(copy[0], out, NULL)
+  ) {
+    g_object_unref(base);
+    return -1;
+  }
+  vips_image_set_int(*out, VIPS_META_PAGE_HEIGHT, height);
+  g_object_unref(base);
+  return 0;
+}
+
 int extract_band(VipsImage *in, VipsImage **out, int band, int num) {
   if (num > 0) {
     return vips_extract_band(in, out, band, "n", num, NULL);

vips/conversion.go

@@ -180,6 +180,17 @@ func vipsExtractArea(in *C.VipsImage, left, top, width, height int) (*C.VipsImag
 	return out, nil
 }
 
+func vipsExtractAreaMultiPage(in *C.VipsImage, left, top, width, height int) (*C.VipsImage, error) {
+	incOpCounter("extractAreaMultiPage")
+	var out *C.VipsImage
+
+	if err := C.extract_area_multi_page(in, &out, C.int(left), C.int(top), C.int(width), C.int(height)); err != 0 {
+		return nil, handleImageError(out)
+	}
+
+	return out, nil
+}
+
 // https://libvips.github.io/libvips/API/current/libvips-conversion.html#vips-extract-band
 func vipsExtractBand(in *C.VipsImage, band, num int) (*C.VipsImage, error) {
 	incOpCounter("extractBand")

vips/conversion.h

@@ -14,6 +14,8 @@ int flip_image(VipsImage *in, VipsImage **out, int direction);
 
 int extract_image_area(VipsImage *in, VipsImage **out, int left, int top,
                        int width, int height);
+int extract_area_multi_page(VipsImage *in, VipsImage **out, int left, int top,
+                       int width, int height);
 
 int extract_band(VipsImage *in, VipsImage **out, int band, int num);
 

vips/error.go

@@ -12,8 +12,7 @@ import (
 
 var (
 	// ErrUnsupportedImageFormat when image type is unsupported
-	ErrUnsupportedImageFormat        = errors.New("unsupported image format")
-	ErrUnsupportedMultiPageOperation = errors.New("unsupported operation for multi-page image")
+	ErrUnsupportedImageFormat = errors.New("unsupported image format")
 )
 
 func handleImageError(out *C.VipsImage) error {

vips/image.go

@@ -1162,15 +1162,20 @@ func (r *ImageRef) AutoRotate() error {
 
 // ExtractArea crops the image to a specified area
 func (r *ImageRef) ExtractArea(left, top, width, height int) error {
-	if err := r.multiPageNotSupported(); err != nil {
-		return err
-	}
-
-	out, err := vipsExtractArea(r.image, left, top, width, height)
-	if err != nil {
-		return err
+	if r.Height() > r.PageHeight() {
+		// use animated extract area if more than 1 pages loaded
+		out, err := vipsExtractAreaMultiPage(r.image, left, top, width, height)
+		if err != nil {
+			return err
+		}
+		r.setImage(out)
+	} else {
+		out, err := vipsExtractArea(r.image, left, top, width, height)
+		if err != nil {
+			return err
+		}
+		r.setImage(out)
 	}
-	r.setImage(out)
 	return nil
 }
 
@@ -1711,14 +1716,6 @@ func (r *ImageRef) newMetadata(format ImageType) *ImageMetadata {
 	}
 }
 
-func (r *ImageRef) multiPageNotSupported() error {
-	if r.Pages() > 1 {
-		return ErrUnsupportedMultiPageOperation
-	}
-
-	return nil
-}
-
 // Pixelate applies a simple pixelate filter to the image
 func Pixelate(imageRef *ImageRef, factor float64) (err error) {
 	if factor < 1 {

vips/image_gif_test.go

@@ -69,3 +69,13 @@ func TestImage_GIF_Animated_Rotate270(t *testing.T) {
 		nil,
 		nil)
 }
+
+func TestImage_GIF_Animated_ExtractArea(t *testing.T) {
+	goldenAnimatedTest(t, resources+"gif-animated.gif",
+		-1,
+		func(img *ImageRef) error {
+			return img.ExtractArea(10, 20, 80, 90)
+		},
+		nil,
+		nil)
+}

vips/image_test.go

@@ -967,15 +967,6 @@ func TestImageRef_JP2K(t *testing.T) {
 	assert.Equal(t, ImageTypeJP2K, metadata.Format)
 }
 
-func TestImageRef_ExtractArea_MultiPage_Unsupported(t *testing.T) {
-	Startup(nil)
-	image, err := NewImageFromFile(resources + "gif-animated.gif")
-	require.NoError(t, err)
-
-	err = image.ExtractArea(1, 2, 3, 4)
-	assert.Error(t, err)
-}
-
 // TODO unit tests to cover:
 // NewImageFromReader failing test
 // NewImageFromFile failing test