Simplify and fix flip (#879)

* Write missing tests for the Flip plugin

* Remove broken code branch in Flip plugin

Removing this unnecessary "shortcut":

- Has no bad effect on complexity
- Removes dependency on Rotate plugin
- Fixes #829
- Actually shortens and simplifies the implementation

packages/plugin-flip/src/index.js

@@ -15,11 +15,6 @@ function flipFn(horizontal, vertical, cb) {
       cb
     );
 
-  if (horizontal && vertical) {
-    // shortcut
-    return this.rotate(180, true, cb);
-  }
-
   const bitmap = Buffer.alloc(this.bitmap.data.length);
   this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function(
     x,

packages/plugin-flip/test/flipping.test.js

@@ -0,0 +1,99 @@
+import { Jimp, mkJGD } from '@jimp/test-utils';
+
+import configure from '@jimp/custom';
+
+import flip from '../src';
+
+const jimp = configure({ plugins: [flip] }, Jimp);
+
+describe('Flipping plugin', () => {
+  it('can flip horizontally', async () => {
+    const src = await jimp.read(
+      mkJGD(
+        'AAAABBBB',
+        'AAABAAAB',
+        'ABABABAB',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'AACCCCAA'
+      )
+    );
+
+    const result = src.flip(true, false);
+
+    result
+      .getJGDSync()
+      .should.be.sameJGD(
+        mkJGD(
+          'BBBBAAAA',
+          'BAAABAAA',
+          'BABABABA',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'AACCCCAA'
+        )
+      );
+  });
+
+  it('can flip vertically', async () => {
+    const src = await jimp.read(
+      mkJGD(
+        'AAAABBBB',
+        'AAABAAAB',
+        'ABABABAB',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'AACCCCAA'
+      )
+    );
+
+    const result = src.flip(false, true);
+
+    result
+      .getJGDSync()
+      .should.be.sameJGD(
+        mkJGD(
+          'AACCCCAA',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'ABABABAB',
+          'AAABAAAB',
+          'AAAABBBB'
+        )
+      );
+  });
+
+  it('can flip both horizontally and vertically at once', async () => {
+    const src = await jimp.read(
+      mkJGD(
+        'AAAABBBB',
+        'AAABAAAB',
+        'ABABABAB',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'CCCCCCCC',
+        'AACCCCAA'
+      )
+    );
+
+    const result = src.flip(true, true);
+
+    result
+      .getJGDSync()
+      .should.be.sameJGD(
+        mkJGD(
+          'AACCCCAA',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'CCCCCCCC',
+          'BABABABA',
+          'BAAABAAA',
+          'BBBBAAAA'
+        )
+      );
+  });
+});