resources/images: Create AutoOrient image filter

Closes #11717

3 files changed, 78 insertions, 6 deletions

diff --git a/resources/image.go b/resources/image.go
index cb0181a5f..6c34795f8 100644
--- a/resources/image.go
+++ b/resources/image.go
@@ -279,8 +279,8 @@ func (i *imageResource) Filter(filters ...any) (images.ImageResource, error) {
 	}
 
 	return i.doWithImageConfig(conf, func(src image.Image) (image.Image, error) {
-		filters := gfilters
-		for j, f := range gfilters {
+		var filters []gift.Filter
+		for _, f := range gfilters {
 			f = images.UnwrapFilter(f)
 			if specProvider, ok := f.(images.ImageProcessSpecProvider); ok {
 				processSpec := specProvider.ImageProcessSpec()
@@ -293,10 +293,14 @@ func (i *imageResource) Filter(filters ...any) (images.ImageResource, error) {
 				if err != nil {
 					return nil, err
 				}
-				// Replace the filter with the new filters.
-				// This slice will be empty if this is just a format conversion.
-				filters = append(filters[:j], append(pFilters, filters[j+1:]...)...)
-
+				filters = append(filters, pFilters...)
+			} else if orientationProvider, ok := f.(images.ImageFilterFromOrientationProvider); ok {
+				tf := orientationProvider.AutoOrient(i.Exif())
+				if tf != nil {
+					filters = append(filters, tf)
+				}
+			} else {
+				filters = append(filters, f)
 			}
 		}
 		return i.Proc.Filter(src, filters...)
diff --git a/resources/images/auto_orient.go b/resources/images/auto_orient.go
new file mode 100644
index 000000000..194efefb5
--- /dev/null
+++ b/resources/images/auto_orient.go
@@ -0,0 +1,60 @@
+// Copyright 2023 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package images
+
+import (
+	"image"
+	"image/draw"
+
+	"github.com/disintegration/gift"
+	"github.com/gohugoio/hugo/resources/images/exif"
+)
+
+var _ gift.Filter = (*autoOrientFilter)(nil)
+
+var transformationFilters = map[int]gift.Filter{
+	2: gift.FlipHorizontal(),
+	3: gift.Rotate180(),
+	4: gift.FlipVertical(),
+	5: gift.Transpose(),
+	6: gift.Rotate270(),
+	7: gift.Transverse(),
+	8: gift.Rotate90(),
+}
+
+type autoOrientFilter struct{}
+
+type ImageFilterFromOrientationProvider interface {
+	AutoOrient(exifInfo *exif.ExifInfo) gift.Filter
+}
+
+func (f autoOrientFilter) Draw(dst draw.Image, src image.Image, options *gift.Options) {
+	panic("not supported")
+}
+
+func (f autoOrientFilter) Bounds(srcBounds image.Rectangle) image.Rectangle {
+	panic("not supported")
+}
+
+func (f autoOrientFilter) AutoOrient(exifInfo *exif.ExifInfo) gift.Filter {
+	if exifInfo != nil {
+		if orientation, ok := exifInfo.Tags["Orientation"].(int); ok {
+			if filter, ok := transformationFilters[orientation]; ok {
+				return filter
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/resources/images/filters.go b/resources/images/filters.go
index 2a1f41a03..572a10d71 100644
--- a/resources/images/filters.go
+++ b/resources/images/filters.go
@@ -174,6 +174,14 @@ func (*Filters) Padding(args ...any) gift.Filter {
 	}
 }
 
+// AutoOrient creates a filter that rotates and flips an image as needed per
+// its EXIF orientation tag.
+func (*Filters) AutoOrient() gift.Filter {
+	return filter{
+		Filter: autoOrientFilter{},
+	}
+}
+
 // Brightness creates a filter that changes the brightness of an image.
 // The percentage parameter must be in range (-100, 100).
 func (*Filters) Brightness(percentage any) gift.Filter {