media/heif: add rotations and visual dimensions accessors

Updates perkeep/perkeep#1094

media/heif/heif.go

@@ -86,8 +86,28 @@ func (it *Item) SpatialExtents() (width, height int, ok bool) {
 	return
 }
 
-// TODO: add HEIF irot rotation accessor, like Image.SpatialExtents.
-// And imir (mirroring).
+// Rotations returns the number of 90 degree rotations counter-clockwise that this
+// image should be rendered at, in the range [0,3].
+func (it *Item) Rotations() int {
+	for _, p := range it.Properties {
+		if p, ok := p.(*bmff.ImageRotation); ok {
+			return int(p.Angle)
+		}
+	}
+	return 0
+}
+
+// VisualDimensions returns the item's width and height after correcting
+// for any rotations.
+func (it *Item) VisualDimensions() (width, height int, ok bool) {
+	width, height, ok = it.SpatialExtents()
+	for i := 0; i < it.Rotations(); i++ {
+		width, height = height, width
+	}
+	return
+}
+
+// TODO: add HEIF imir (mirroring) accessor, like Image.SpatialExtents.
 
 // Open returns a handle to access a HEIF file.
 func Open(f io.ReaderAt) *File {

media/heif/heif_test.go

@@ -79,6 +79,33 @@ func TestAll(t *testing.T) {
 	}
 }
 
+func TestRotations(t *testing.T) {
+	f, err := os.Open("testdata/rotate.heic")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	h := Open(f)
+	it, err := h.PrimaryItem()
+	if err != nil {
+		t.Fatalf("PrimaryItem: %v", err)
+	}
+	if r := it.Rotations(); r != 3 {
+		t.Errorf("Rotations = %v; want %v", r, 3)
+	}
+	sw, sh, ok := it.SpatialExtents()
+	if !ok {
+		t.Fatalf("expected spatial extents")
+	}
+	vw, vh, ok := it.VisualDimensions()
+	if !ok {
+		t.Fatalf("expected visual dimensions")
+	}
+	if vw != sh || vh != sw {
+		t.Errorf("visual dimensions = %v, %v; want %v, %v", vw, vh, sh, sw)
+	}
+}
+
 type walkFunc func(exif.FieldName, *tiff.Tag) error
 
 func (f walkFunc) Walk(name exif.FieldName, tag *tiff.Tag) error {