Add support for any rotation angle (#791)

Allow to provide any positive or negative multiple of 90 to `.rotate(...)`.
Negative angles and angles above 360 are converted to valid 0/90/180/270
rotations (0 rotations are still ignored).

Changes:
- [Node] Add `useExifOrientation` internal variable to know if the Exif
  orientation must be used instead of the provided angle. This allows to save a
  negative angle in the `angle` option, because the `-1` special case is not
  needed.

- [Node] Change check for planed-rotation in extract, to prepare a
  rotation before extraction: check with both `angle` and `useExifOrientation`
  options.
  I think this check contains a bit too much logics on rotation options. Maybe
  we could move this condition to a dedicated function.

- [C++] Separate `CalculateRotationAndFlip` into two generic functions:
  - `CalculateExifRotationAndFlip`: Calculate the angle of rotation and
    need-to-flip for the given Exif orientation.
  - `CalculateAngleRotation`: Calculate the rotation for the given angle.

  One or the other function is used to calculate the rotation, depending on
  wether the Exif orientation tag or the provided angle must be used.

- Add unit tests for `-3690`, `-450`, `-90`, `90`, `450`, `3690` and `-3780`,
  `-540`, `0`, `180`, `540`, `3780` rotations
- Add `320x240` fixture image for tests.

Unrelated changes (squashed):
- Add ncoden to the list of contributors

src/pipeline.cc

@@ -81,16 +81,12 @@ class PipelineWorker : public Nan::AsyncWorker {
 
       // Calculate angle of rotation
       VipsAngle rotation;
-      bool flip;
-      bool flop;
-      std::tie(rotation, flip, flop) = CalculateRotationAndFlip(baton->angle, image);
-      if (flip && !baton->flip) {
-        // Add flip operation due to EXIF mirroring
-        baton->flip = TRUE;
-      }
-      if (flop && !baton->flop) {
-        // Add flip operation due to EXIF mirroring
-        baton->flop = TRUE;
+      if (baton->useExifOrientation) {
+        // Rotate and flip image according to Exif orientation
+        // (ignore the requested rotation and flip)
+        std::tie(rotation, baton->flip, baton->flop) = CalculateExifRotationAndFlip(sharp::ExifOrientation(image));
+      } else {
+        rotation = CalculateAngleRotation(baton->angle);
       }
 
       // Rotate pre-extract
@@ -1065,39 +1061,43 @@ class PipelineWorker : public Nan::AsyncWorker {
   std::vector<v8::Local<v8::Object>> buffersToPersist;
 
   /*
-    Calculate the angle of rotation and need-to-flip for the output image.
-    In order of priority:
-     1. Use explicitly requested angle (supports 90, 180, 270)
-     2. Use input image EXIF Orientation header - supports mirroring
-     3. Otherwise default to zero, i.e. no rotation
+    Calculate the angle of rotation and need-to-flip for the given Exif orientation
+    By default, returns zero, i.e. no rotation.
   */
   std::tuple<VipsAngle, bool, bool>
-  CalculateRotationAndFlip(int const angle, vips::VImage image) {
+  CalculateExifRotationAndFlip(int const exifOrientation) {
     VipsAngle rotate = VIPS_ANGLE_D0;
     bool flip = FALSE;
     bool flop = FALSE;
-    if (angle == -1) {
-      switch (sharp::ExifOrientation(image)) {
-        case 6: rotate = VIPS_ANGLE_D90; break;
-        case 3: rotate = VIPS_ANGLE_D180; break;
-        case 8: rotate = VIPS_ANGLE_D270; break;
-        case 2: flop = TRUE; break;  // flop 1
-        case 7: flip = TRUE; rotate = VIPS_ANGLE_D90; break;  // flip 6
-        case 4: flop = TRUE; rotate = VIPS_ANGLE_D180; break;  // flop 3
-        case 5: flip = TRUE; rotate = VIPS_ANGLE_D270; break;  // flip 8
-      }
-    } else {
-      if (angle == 90) {
-        rotate = VIPS_ANGLE_D90;
-      } else if (angle == 180) {
-        rotate = VIPS_ANGLE_D180;
-      } else if (angle == 270) {
-        rotate = VIPS_ANGLE_D270;
-      }
+    switch (exifOrientation) {
+      case 6: rotate = VIPS_ANGLE_D90; break;
+      case 3: rotate = VIPS_ANGLE_D180; break;
+      case 8: rotate = VIPS_ANGLE_D270; break;
+      case 2: flop = TRUE; break;  // flop 1
+      case 7: flip = TRUE; rotate = VIPS_ANGLE_D90; break;  // flip 6
+      case 4: flop = TRUE; rotate = VIPS_ANGLE_D180; break;  // flop 3
+      case 5: flip = TRUE; rotate = VIPS_ANGLE_D270; break;  // flip 8
     }
     return std::make_tuple(rotate, flip, flop);
   }
 
+  /*
+    Calculate the rotation for the given angle.
+    Supports any positive or negative angle that is a multiple of 90.
+  */
+  VipsAngle
+  CalculateAngleRotation(int angle) {
+    angle = angle % 360;
+    if (angle < 0)
+      angle = 360 + angle;
+    switch (angle) {
+      case 90: return VIPS_ANGLE_D90;
+      case 180: return VIPS_ANGLE_D180;
+      case 270: return VIPS_ANGLE_D270;
+    }
+    return VIPS_ANGLE_D0;
+  }
+
   /*
     Assemble the suffix argument to dzsave, which is the format (by extname)
     alongisde comma-separated arguments to the corresponding `formatsave` vips
@@ -1222,6 +1222,7 @@ NAN_METHOD(pipeline) {
   baton->gamma = AttrTo<double>(options, "gamma");
   baton->greyscale = AttrTo<bool>(options, "greyscale");
   baton->normalise = AttrTo<bool>(options, "normalise");
+  baton->useExifOrientation = AttrTo<bool>(options, "useExifOrientation");
   baton->angle = AttrTo<int32_t>(options, "angle");
   baton->rotateBeforePreExtract = AttrTo<bool>(options, "rotateBeforePreExtract");
   baton->flip = AttrTo<bool>(options, "flip");

src/pipeline.h

@@ -81,6 +81,7 @@ struct PipelineBaton {
   double gamma;
   bool greyscale;
   bool normalise;
+  bool useExifOrientation;
   int angle;
   bool rotateBeforePreExtract;
   bool flip;
@@ -158,6 +159,7 @@ struct PipelineBaton {
     gamma(0.0),
     greyscale(false),
     normalise(false),
+    useExifOrientation(false),
     angle(0),
     flip(false),
     flop(false),