feat: add ability to pass in custom widths (#55)

README.md

@@ -68,7 +68,7 @@ https://your-subdomain.imgix.net/images/demo.png?w=7400&s=a5dd7dda1dbac613f0475f
 https://your-subdomain.imgix.net/images/demo.png?w=8192&s=9fbd257c53e770e345ce3412b64a3452 8192w
 ```
 
-**Fixed image rendering**
+### Fixed image rendering
 
 In cases where enough information is provided about an image's dimensions, `to_srcset` will instead build a `srcset` that will allow for an image to be served at different resolutions. The parameters taken into consideration when determining if an image is fixed-width are `w`, `h`, and `ar`. By invoking `to_srcset` with either a width **or** the height and aspect ratio (along with `fit=crop`, typically) provided, a different `srcset` will be generated for a fixed-size image instead.
 
@@ -91,7 +91,28 @@ https://your-subdomain.imgix.net/images/demo.png?h=800&ar=3%3A2&fit=crop&dpr=5&s
 
 For more information to better understand `srcset`, we highly recommend [Eric Portis' "Srcset and sizes" article](https://ericportis.com/posts/2014/srcset-sizes/) which goes into depth about the subject.
 
-**Width Tolerance**
+### Custom Widths
+
+In situations where specific widths are desired when generating `srcset` pairs, a user can specify them by passing an array of integers to the `widths` keyword argument.
+
+```rb
+@client ||= Imgix::Client.new(host: 'testing.imgix.net', include_library_param: false)
+.path('image.jpg')
+.to_srcset(widths: [100, 500, 1000, 1800])
+```
+
+Will generate the following `srcset` of width pairs:
+
+```html
+https://testing.imgix.net/image.jpg?w=100 100w,
+https://testing.imgix.net/image.jpg?w=500 500w,
+https://testing.imgix.net/image.jpg?w=1000 1000w,
+https://testing.imgix.net/image.jpg?w=1800 1800w
+```
+
+Please note that in situations where a `srcset` is being rendered as a [fixed image](#fixed-image-rendering), any custom `widths` passed in will be ignored. Additionally, if both `widths` and a `width_tolerance` are passed to the `to_srcset` method, the custom widths list will take precedence.
+
+### Width Tolerance
 
 The `srcset` width tolerance dictates the maximum tolerated size difference between an image's downloaded size and its rendered size. For example: setting this value to 0.1 means that an image will not render more than 10% larger or smaller than its native size. In practice, the image URLs generated for a width-based srcset attribute will grow by twice this rate. A lower tolerance means images will render closer to their native size (thereby reducing rendering artifacts), but a large srcset list will be generated and consequently users may experience lower rates of cache-hit for pre-rendered images on your site.
 

lib/imgix/path.rb

@@ -84,7 +84,7 @@ def method_missing(method, *args, &block)
       end
     end
 
-    def to_srcset(width_tolerance: DEFAULT_WIDTH_TOLERANCE, **params)
+    def to_srcset(widths: [], width_tolerance: DEFAULT_WIDTH_TOLERANCE, **params)
       prev_options = @options.dup
       @options.merge!(params)
 
@@ -95,7 +95,7 @@ def to_srcset(width_tolerance: DEFAULT_WIDTH_TOLERANCE, **params)
       if ((width) || (height && aspect_ratio))
         srcset = build_dpr_srcset(@options)
       else
-        srcset = build_srcset_pairs(width_tolerance: width_tolerance, params: @options)
+        srcset = build_srcset_pairs(widths: widths, width_tolerance: width_tolerance, params: @options)
       end
 
       @options = prev_options
@@ -128,16 +128,19 @@ def has_query?
       query.length > 0
     end
 
-    def build_srcset_pairs(width_tolerance:, params:)
+    def build_srcset_pairs(widths:, width_tolerance:, params:)
       srcset = ''
 
-      unless width_tolerance == DEFAULT_WIDTH_TOLERANCE
-        widths = TARGET_WIDTHS.call(width_tolerance)
+      if !widths.empty?
+        validate_widths!(widths)
+        srcset_widths = widths
+      elsif width_tolerance != DEFAULT_WIDTH_TOLERANCE
+        srcset_widths = TARGET_WIDTHS.call(width_tolerance)
       else
-        widths = @target_widths
+        srcset_widths = @target_widths
       end
 
-      for width in widths do
+      for width in srcset_widths do
         params['w'.to_sym] = width
         srcset += "#{to_url(params)} #{width}w,\n"
       end
@@ -156,5 +159,17 @@ def build_dpr_srcset(params)
 
       srcset[0..-3]
     end
+
+    def validate_widths!(widths)
+      unless widths.is_a? Array
+        raise ArgumentError, "The widths argument must be passed a valid array of integers"
+      else
+        positive_integers = widths.all? {|i| i.is_a?(Integer) and i > 0}
+        unless positive_integers
+          raise ArgumentError, "A custom widths array must only contain positive integer values"  
+        end
+      end
+    end
+
   end
 end

test/units/srcset_test.rb

@@ -8,7 +8,7 @@ def test_no_parameters
             expected_number_of_pairs = 31
             assert_equal expected_number_of_pairs, srcset.split(',').length
         end
-        
+
         def test_srcset_pair_values
             resolutions = [100, 116, 134, 156, 182, 210, 244, 282,
                 328, 380, 442, 512, 594, 688, 798, 926,
@@ -67,7 +67,7 @@ def test_srcset_signs_urls
                 assert_equal expected_signature, generated_signature
             }
         end
-    
+
         private
             def srcset
                 @client ||= Imgix::Client.new(host: 'testing.imgix.net', secure_url_token: 'MYT0KEN', include_library_param: false).path('image.jpg').to_srcset(w:100)
@@ -186,7 +186,7 @@ def test_srcset_signs_urls
 
                 signature_base = 'MYT0KEN' + '/image.jpg' + params;
                 expected_signature = Digest::MD5.hexdigest(signature_base)
-                
+
                 assert_equal expected_signature, generated_signature
             }
         end
@@ -303,7 +303,7 @@ def test_srcset_signs_urls
 
                 signature_base = 'MYT0KEN' + '/image.jpg' + params;
                 expected_signature = Digest::MD5.hexdigest(signature_base)
-                
+
                 assert_equal expected_signature, generated_signature
             }
         end
@@ -337,7 +337,6 @@ def test_srcset_within_bounds
             # parse out the width descriptor as an integer
             min = min.split(' ')[1].to_i
             max = max[max.length - 1].split(' ')[1].to_i
-
             assert_operator min, :>=, 100
             assert_operator max, :<=, 8192
         end
@@ -397,4 +396,83 @@ def srcset
                 @client ||= Imgix::Client.new(host: 'testing.imgix.net', secure_url_token: 'MYT0KEN', include_library_param: false).path('image.jpg').to_srcset(width_tolerance: 0.20)
             end
     end
-end
+
+    class SrcsetCustomWidths < Imgix::Test
+        def test_srcset_generates_width_pairs
+            expected_number_of_pairs = 4
+            assert_equal expected_number_of_pairs, srcset.split(',').length
+        end
+
+        def test_srcset_pair_values
+            resolutions = [100, 500, 1000, 1800]
+            srclist = srcset.split(',').map { |srcset_split|
+                srcset_split.split(' ')[1].to_i
+            }
+
+            for i in 0..srclist.length - 1 do
+                assert_equal(srclist[i], resolutions[i])
+            end
+        end
+
+        def test_srcset_within_bounds
+            min, *max = srcset.split(',')
+
+            # parse out the width descriptor as an integer
+            min = min.split(' ')[1].to_i
+            max = max[max.length - 1].split(' ')[1].to_i
+
+            assert_operator min, :>=, @widths[0]
+            assert_operator max, :<=, @widths[-1]
+        end
+
+        def test_invalid_widths_input_emits_error
+            assert_raises(ArgumentError) {
+                Imgix::Client.new(host: 'testing.imgix.net')
+                .path('image.jpg')
+                .to_srcset(widths: 'abc')
+            }
+        end
+
+        def test_non_integer_array_emits_error
+            assert_raises(ArgumentError) {
+                Imgix::Client.new(host: 'testing.imgix.net')
+                .path('image.jpg')
+                .to_srcset(widths: [100, 200, false])
+            }
+        end
+
+        def test_negative_integer_array_emits_error
+            assert_raises(ArgumentError) {
+                Imgix::Client.new(host: 'testing.imgix.net')
+                .path('image.jpg')
+                .to_srcset(widths: [100, 200, -100])
+            }
+        end
+
+        def test_with_param_after
+            srcset = Imgix::Client.new(host: 'testing.imgix.net', secure_url_token: 'MYT0KEN', include_library_param: false)
+            .path('image.jpg')
+            .to_srcset(widths: [100, 200, 300], h:1000, fit:"clip")
+            assert_includes(srcset, "h=")
+            assert(not(srcset.include? "widths="))
+        end
+
+        def test_with_param_before
+            srcset = Imgix::Client.new(host: 'testing.imgix.net', secure_url_token: 'MYT0KEN', include_library_param: false)
+            .path('image.jpg')
+            .to_srcset(h:1000, fit:"clip", widths: [100, 200, 300])
+            assert_includes(srcset, "h=")
+            assert(not(srcset.include? "widths="))
+        end
+
+        private
+            def srcset
+                @widths = [100, 500, 1000, 1800]
+                @client ||= Imgix::Client.new(
+                    host: 'testing.imgix.net',
+                    include_library_param: false)
+                    .path('image.jpg')
+                    .to_srcset(widths: @widths)
+            end
+    end
+end