From b89144a052bf70f221aa0e805efcaf6e769db53f Mon Sep 17 00:00:00 2001
From: Matthew Kobs <matt.kobs@cph.org>
Date: Mon, 7 Nov 2016 11:33:35 -0600
Subject: [PATCH] Add ability to set dpi on physical chunk

---
 lib/chunky_png/chunk.rb            | 10 ++++++++++
 spec/chunky_png/datastream_spec.rb |  9 +++++++++
 2 files changed, 19 insertions(+)

diff --git a/lib/chunky_png/chunk.rb b/lib/chunky_png/chunk.rb
index 0b9f51b9..dbbb3e59 100644
--- a/lib/chunky_png/chunk.rb
+++ b/lib/chunky_png/chunk.rb
@@ -338,11 +338,21 @@ def dpix
         ppux * METERS_PER_INCH
       end
 
+      def dpix=(value)
+        @unit = :meters
+        @ppux = (value / METERS_PER_INCH).round
+      end
+
       def dpiy
         raise ChunkyPNG::UnitsUnknown, 'the PNG specifies its physical aspect ratio, but does not specify the units of its pixels\' physical dimensions' unless unit == :meters
         ppuy * METERS_PER_INCH
       end
 
+      def dpiy=(value)
+        @unit = :meters
+        @ppuy = (value / METERS_PER_INCH).round
+      end
+
       def self.read(type, content)
         ppux, ppuy, unit = content.unpack('NNC')
         unit = unit == 1 ? :meters : :unknown
diff --git a/spec/chunky_png/datastream_spec.rb b/spec/chunky_png/datastream_spec.rb
index 1b095a2b..bbc3b0a8 100644
--- a/spec/chunky_png/datastream_spec.rb
+++ b/spec/chunky_png/datastream_spec.rb
@@ -55,5 +55,14 @@
       expect{physical_chunk.dpix}.to raise_error(ChunkyPNG::UnitsUnknown)
       expect{physical_chunk.dpiy}.to raise_error(ChunkyPNG::UnitsUnknown)
     end
+
+    it 'should set units and ppu correctly when setting dpi' do
+      physical_chunk = ChunkyPNG::Chunk::Physical.new(9001, 9001, :unknown)
+      physical_chunk.dpix = 72
+      physical_chunk.dpiy = 72
+      expect(physical_chunk.unit).to eql :meters
+      expect(physical_chunk.ppux).to eql 2835
+      expect(physical_chunk.ppuy).to eql 2835
+    end
   end
 end