Proper handling of the EXIF cases.

Kudos to
https://www.daveperrett.com/articles/2012/07/28/exif-orientation-handling-is-a-ghetto/

Signed-off-by: Yoan Blanc <[email protected]>

resize.go

@@ -518,15 +518,15 @@ func calculateRotationAndFlip(image *C.VipsImage, angle Angle) (Angle, bool) {
 		break // flip 1
 	case 7:
 		flip = true
-		rotate = D90
+		rotate = D270
 		break // flip 6
 	case 4:
 		flip = true
 		rotate = D180
 		break // flip 3
 	case 5:
 		flip = true
-		rotate = D270
+		rotate = D90
 		break // flip 8
 	}
 

resize_test.go

@@ -3,6 +3,7 @@ package bimg
 import (
 	"bytes"
 	"crypto/md5"
+	"fmt"
 	"image"
 	"image/jpeg"
 	"io/ioutil"
@@ -393,6 +394,65 @@ func TestResizePngWithTransparency(t *testing.T) {
 	Write("fixtures/transparent_out.png", newImg)
 }
 
+func TestRotationAndFlip(t *testing.T) {
+	files := []struct {
+		Name  string
+		Angle Angle
+		Flip  bool
+	}{
+		{"Landscape_1", 0, false},
+		{"Landscape_2", 0, true},
+		{"Landscape_3", D180, false},
+		{"Landscape_4", D180, true},
+		{"Landscape_5", D90, true},
+		{"Landscape_6", D90, false},
+		{"Landscape_7", D270, true},
+		{"Landscape_8", D270, false},
+		{"Portrait_1", 0, false},
+		{"Portrait_2", 0, true},
+		{"Portrait_3", D180, false},
+		{"Portrait_4", D180, true},
+		{"Portrait_5", D90, true},
+		{"Portrait_6", D90, false},
+		{"Portrait_7", D270, true},
+		{"Portrait_8", D270, false},
+	}
+
+	for _, file := range files {
+		img, err := os.Open(fmt.Sprintf("fixtures/exif/%s.jpg", file.Name))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		buf, err := ioutil.ReadAll(img)
+		if err != nil {
+			t.Fatal(err)
+		}
+		img.Close()
+
+		image, _, err := loadImage(buf)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		angle, flip := calculateRotationAndFlip(image, D0)
+		if angle != file.Angle {
+			t.Errorf("Rotation for %v expected to be %v. got %v", file.Name, file.Angle, angle)
+		}
+		if flip != file.Flip {
+			t.Errorf("Flip for %v expected to be %v. got %v", file.Name, file.Flip, flip)
+		}
+
+		// Visual debugging.
+		newImg, err := Resize(buf, Options{})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		Write(fmt.Sprintf("fixtures/exif/%s_out.jpg", file.Name), newImg)
+	}
+}
+
 func TestIfBothSmartCropOptionsAreIdentical(t *testing.T) {
 	if !(VipsMajorVersion >= 8 && VipsMinorVersion > 4) {
 		t.Skipf("Skipping this test, libvips doesn't meet version requirement %s > 8.4", VipsVersion)