Merge pull request #102 from lencioni/croptimization

Optimize crop! when only cropping top/bottom

lib/chunky_png/canvas/operations.rb

@@ -175,11 +175,18 @@ def crop!(x, y, crop_width, crop_height)
           raise ChunkyPNG::OutOfBounds, 'Original image height is too small!'
         end
 
-        new_pixels = []
-        for cy in 0...crop_height do
-          new_pixels.concat pixels.slice((cy + y) * width + x, crop_width)
+        if crop_width == width && x == 0
+          # We only need to crop off the top and/or bottom, so we can take a
+          # shortcut.
+          replace_canvas!(crop_width, crop_height,
+                          pixels.slice(y * width, width * crop_height))
+        else
+          new_pixels = []
+          for cy in 0...crop_height do
+            new_pixels.concat pixels.slice((cy + y) * width + x, crop_width)
+          end
+          replace_canvas!(crop_width, crop_height, new_pixels)
         end
-        replace_canvas!(crop_width, crop_height, new_pixels)
       end
 
       # Flips the image horizontally, leaving the original intact.

spec/chunky_png/canvas/operations_spec.rb

@@ -48,22 +48,46 @@
   end
 
   describe '#crop!' do
-    it "should crop the right pixels from the original canvas" do
-      subject.crop!(10, 5, 4, 8)
-      expect(subject).to eql reference_canvas('cropped')
-    end
+    context 'when cropping both width and height' do
+      let(:crop_opts) { [10, 5, 4, 8] }
+
+      it "should crop the right pixels from the original canvas" do
+        subject.crop!(*crop_opts)
+        expect(subject).to eql reference_canvas('cropped')
+      end
 
-    it "should have a new width and height" do
-      expect { subject.crop!(10, 5, 4, 8) }.to change { subject.dimension }.
-          from(ChunkyPNG::Dimension('16x16')).to(ChunkyPNG::Dimension('4x8'))
+      it "should have a new width and height" do
+        expect { subject.crop!(*crop_opts) }.to change { subject.dimension }.
+            from(ChunkyPNG::Dimension('16x16')).to(ChunkyPNG::Dimension('4x8'))
+      end
+
+      it "should return itself" do
+        expect(subject.crop!(*crop_opts)).to equal(subject)
+      end
     end
 
-    it "should raise an exception when the cropped image falls outside the oiginal image" do
-      expect { subject.crop!(16, 16, 2, 2) }.to raise_error(ChunkyPNG::OutOfBounds)
+    context "when cropping just the height" do
+      let(:crop_opts) { [0, 5, 16, 8] }
+
+      it "should crop the right pixels from the original canvas" do
+        subject.crop!(*crop_opts)
+        expect(subject).to eql reference_canvas('cropped_height')
+      end
+
+      it "should have a new width and height" do
+        expect { subject.crop!(*crop_opts) }.to change { subject.dimension }.
+            from(ChunkyPNG::Dimension('16x16')).to(ChunkyPNG::Dimension('16x8'))
+      end
+
+      it "should return itself" do
+        expect(subject.crop!(*crop_opts)).to equal(subject)
+      end
     end
 
-    it "should return itself" do
-      expect(subject.crop!(10, 5, 4, 8)).to equal(subject)
+    context "when the cropped image falls outside the original image" do
+      it "should raise an exception" do
+        expect { subject.crop!(16, 16, 2, 2) }.to raise_error(ChunkyPNG::OutOfBounds)
+      end
     end
   end