From 1a5314d0d0cb55ddea621e4d0b963b170c2d9b8b Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Thu, 15 Jan 2026 18:40:00 +0000
Subject: [PATCH 1/7] Start implementing hsluv versions of the color functions

---
 lib/glug.rb                        |  1 +
 lib/glug/hsluv_modifiers.rb        | 23 +++++++++++++++++
 spec/fixtures/color_functions.glug | 19 ++++++++++++++
 spec/fixtures/color_functions.json | 40 ++++++++++++++++++++++++++++++
 spec/lib/glug/stylesheet_spec.rb   |  9 +++++++
 5 files changed, 92 insertions(+)
 create mode 100644 lib/glug/hsluv_modifiers.rb
 create mode 100644 spec/fixtures/color_functions.glug
 create mode 100644 spec/fixtures/color_functions.json

diff --git a/lib/glug.rb b/lib/glug.rb
index 113454d..58c8b28 100644
--- a/lib/glug.rb
+++ b/lib/glug.rb
@@ -10,5 +10,6 @@ module Glug # :nodoc:
 require_relative 'glug/stylesheet'
 require_relative 'glug/layer'
 require_relative 'glug/extensions'
+require_relative 'glug/hsluv_modifiers'
 require_relative 'glug/stylesheet_dsl'
 require_relative 'glug/layer_dsl'
diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
new file mode 100644
index 0000000..39e4eaf
--- /dev/null
+++ b/lib/glug/hsluv_modifiers.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'chroma'
+require 'hsluv'
+
+module Chroma
+  # Add hsluv versions of the color functions to chroma
+  class Color
+    def darkenp(amount = 10)
+      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      new_l = [l - amount, 0].max
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, new_l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
+
+    def lightenp(amount = 10)
+      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      new_l = [l + amount, 100].min
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, new_l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
+  end
+end
diff --git a/spec/fixtures/color_functions.glug b/spec/fixtures/color_functions.glug
new file mode 100644
index 0000000..ae51520
--- /dev/null
+++ b/spec/fixtures/color_functions.glug
@@ -0,0 +1,19 @@
+version 8
+name 'My first stylesheet'
+source :shortbread, type: 'vector', url: 'https://vector.openstreetmap.org/shortbread_v1/tilejson.json'
+
+layer(:darken, source: :shortbread) do
+  line_color 0x998877.chroma(:darken, 20)
+end
+
+layer(:darkenp, source: :shortbread) do
+  line_color 0x998877.chroma(:darkenp, 20)
+end
+
+layer(:lighten, source: :shortbread) do
+  line_color 0x998877.chroma(:lighten, 20)
+end
+
+layer(:lightenp, source: :shortbread) do
+  line_color 0x998877.chroma(:lightenp, 20)
+end
diff --git a/spec/fixtures/color_functions.json b/spec/fixtures/color_functions.json
new file mode 100644
index 0000000..030dff0
--- /dev/null
+++ b/spec/fixtures/color_functions.json
@@ -0,0 +1,40 @@
+{
+  "version":8,
+  "name":"My first stylesheet",
+  "sources":{
+    "shortbread":{
+      "type":"vector",
+      "url":"https://vector.openstreetmap.org/shortbread_v1/tilejson.json"
+    }
+  },
+  "layers":[
+    {
+      "paint":{"line-color":"#615549"},
+      "source":"shortbread",
+      "id":"darken",
+      "source-layer":"darken",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#62574b"},
+      "source":"shortbread",
+      "id":"darkenp",
+      "source-layer":"darkenp",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#c5bbb1"},
+      "source":"shortbread",
+      "id":"lighten",
+      "source-layer":"lighten",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#d3bca5"},
+      "source":"shortbread",
+      "id":"lightenp",
+      "source-layer":"lightenp",
+      "type":"line"
+    }
+  ]
+}
diff --git a/spec/lib/glug/stylesheet_spec.rb b/spec/lib/glug/stylesheet_spec.rb
index f25811e..7c07093 100644
--- a/spec/lib/glug/stylesheet_spec.rb
+++ b/spec/lib/glug/stylesheet_spec.rb
@@ -113,5 +113,14 @@
       output = File.read(File.join(fixture_dir, 'expression_ivars.json'))
       expect(stylesheet.to_json).to eql(output.strip)
     end
+
+    it 'handles color functions' do
+      glug = File.read(File.join(fixture_dir, 'color_functions.glug'))
+      stylesheet = described_class.new(base_dir: fixture_dir) do
+        instance_eval(glug)
+      end
+      output = File.read(File.join(fixture_dir, 'color_functions.json'))
+      expect(stylesheet.to_json).to eql(output.strip)
+    end
   end
 end

From 323745830307140ab333b436fed9837e4afeba00 Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Thu, 15 Jan 2026 19:01:40 +0000
Subject: [PATCH 2/7] Add saturatep/desaturatep

---
 lib/glug/hsluv_modifiers.rb        | 14 ++++++++++++++
 spec/fixtures/color_functions.glug | 16 ++++++++++++++++
 spec/fixtures/color_functions.json | 28 ++++++++++++++++++++++++++++
 3 files changed, 58 insertions(+)

diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index 39e4eaf..8368c12 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -19,5 +19,19 @@ def lightenp(amount = 10)
       rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, new_l))
       Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
+
+    def saturatep(amount = 10)
+      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      new_s = [s + amount, 100].min
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, new_s, l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
+
+    def desaturatep(amount = 10)
+      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      new_s = [s - amount, 0].max
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, new_s, l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
   end
 end
diff --git a/spec/fixtures/color_functions.glug b/spec/fixtures/color_functions.glug
index ae51520..8a67542 100644
--- a/spec/fixtures/color_functions.glug
+++ b/spec/fixtures/color_functions.glug
@@ -17,3 +17,19 @@ end
 layer(:lightenp, source: :shortbread) do
   line_color 0x998877.chroma(:lightenp, 20)
 end
+
+layer(:saturate, source: :shortbread) do
+  line_color 0x998877.chroma(:saturate, 20)
+end
+
+layer(:saturatep, source: :shortbread) do
+  line_color 0x998877.chroma(:saturatep, 20)
+end
+
+layer(:desaturate, source: :shortbread) do
+  line_color 0x998877.chroma(:desaturate, 20)
+end
+
+layer(:desaturatep, source: :shortbread) do
+  line_color 0x998877.chroma(:desaturatep, 20)
+end
diff --git a/spec/fixtures/color_functions.json b/spec/fixtures/color_functions.json
index 030dff0..33ed32e 100644
--- a/spec/fixtures/color_functions.json
+++ b/spec/fixtures/color_functions.json
@@ -35,6 +35,34 @@
       "id":"lightenp",
       "source-layer":"lightenp",
       "type":"line"
+    },
+    {
+      "paint":{"line-color":"#b1885f"},
+      "source":"shortbread",
+      "id":"saturate",
+      "source-layer":"saturate",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#a28665"},
+      "source":"shortbread",
+      "id":"saturatep",
+      "source-layer":"saturatep",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#888888"},
+      "source":"shortbread",
+      "id":"desaturate",
+      "source-layer":"desaturate",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#8e8a87"},
+      "source":"shortbread",
+      "id":"desaturatep",
+      "source-layer":"desaturatep",
+      "type":"line"
     }
   ]
 }

From 01da68a8064bd5605487848ab8228bdfce8e8d22 Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Fri, 16 Jan 2026 09:26:07 +0000
Subject: [PATCH 3/7] Allow greyscale to work with no parameters, and add
 greyscalep

---
 lib/glug/extensions.rb             |  7 ++++---
 lib/glug/hsluv_modifiers.rb        |  7 +++++++
 spec/fixtures/color_functions.glug |  8 ++++++++
 spec/fixtures/color_functions.json | 14 ++++++++++++++
 4 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/lib/glug/extensions.rb b/lib/glug/extensions.rb
index b7e0708..bd82e8b 100644
--- a/lib/glug/extensions.rb
+++ b/lib/glug/extensions.rb
@@ -6,11 +6,12 @@
 # Colour methods on Integer
 class Integer
   # rubocop:disable Style/StringConcatenation, Naming/MethodParameterName
-  def chroma_hex(op, p)
-    ('#' + to_s(16).rjust(6, '0')).paint.send(op, p).to_hex
+  def chroma_hex(op, p = nil)
+    color = ('#' + to_s(16).rjust(6, '0')).paint
+    (p.nil? ? color.send(op) : color.send(op, p)).to_hex
   end
 
-  def chroma(op, p)
+  def chroma(op, p = nil)
     chroma_hex(op, p).gsub('#', '0x').to_i(16)
   end
 
diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index 8368c12..b76fd81 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -33,5 +33,12 @@ def desaturatep(amount = 10)
       rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, new_s, l))
       Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
+
+    def greyscalep
+      h, _s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, 0, l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
+    alias grayscalep greyscalep
   end
 end
diff --git a/spec/fixtures/color_functions.glug b/spec/fixtures/color_functions.glug
index 8a67542..f5fc2ba 100644
--- a/spec/fixtures/color_functions.glug
+++ b/spec/fixtures/color_functions.glug
@@ -33,3 +33,11 @@ end
 layer(:desaturatep, source: :shortbread) do
   line_color 0x998877.chroma(:desaturatep, 20)
 end
+
+layer(:greyscale, source: :shortbread) do
+  line_color 0x998877.chroma(:greyscale)
+end
+
+layer(:greyscalep, source: :shortbread) do
+  line_color 0x998877.chroma(:greyscalep)
+end
diff --git a/spec/fixtures/color_functions.json b/spec/fixtures/color_functions.json
index 33ed32e..8535e45 100644
--- a/spec/fixtures/color_functions.json
+++ b/spec/fixtures/color_functions.json
@@ -63,6 +63,20 @@
       "id":"desaturatep",
       "source-layer":"desaturatep",
       "type":"line"
+    },
+    {
+      "paint":{"line-color":"#888888"},
+      "source":"shortbread",
+      "id":"greyscale",
+      "source-layer":"greyscale",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#8b8b8b"},
+      "source":"shortbread",
+      "id":"greyscalep",
+      "source-layer":"greyscalep",
+      "type":"line"
     }
   ]
 }

From e7ffc83dca7cde54aa0521474f2e475f8df991f5 Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Fri, 16 Jan 2026 13:59:31 +0000
Subject: [PATCH 4/7] Implement spinp

---
 lib/glug/hsluv_modifiers.rb        |  7 +++++++
 spec/fixtures/color_functions.glug |  8 ++++++++
 spec/fixtures/color_functions.json | 14 ++++++++++++++
 3 files changed, 29 insertions(+)

diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index b76fd81..0db95e5 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -40,5 +40,12 @@ def greyscalep
       Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
     alias grayscalep greyscalep
+
+    def spinp(amount = 0)
+      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      new_h = (h + amount) % 360
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(new_h, s, l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
   end
 end
diff --git a/spec/fixtures/color_functions.glug b/spec/fixtures/color_functions.glug
index f5fc2ba..32a833e 100644
--- a/spec/fixtures/color_functions.glug
+++ b/spec/fixtures/color_functions.glug
@@ -41,3 +41,11 @@ end
 layer(:greyscalep, source: :shortbread) do
   line_color 0x998877.chroma(:greyscalep)
 end
+
+layer(:spin, source: :shortbread) do
+  line_color 0x998877.chroma(:spin, 20)
+end
+
+layer(:spinp, source: :shortbread) do
+  line_color 0x998877.chroma(:spinp, 20)
+end
diff --git a/spec/fixtures/color_functions.json b/spec/fixtures/color_functions.json
index 8535e45..17ddd60 100644
--- a/spec/fixtures/color_functions.json
+++ b/spec/fixtures/color_functions.json
@@ -77,6 +77,20 @@
       "id":"greyscalep",
       "source-layer":"greyscalep",
       "type":"line"
+    },
+    {
+      "paint":{"line-color":"#999377"},
+      "source":"shortbread",
+      "id":"spin",
+      "source-layer":"spin",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#918b77"},
+      "source":"shortbread",
+      "id":"spinp",
+      "source-layer":"spinp",
+      "type":"line"
     }
   ]
 }

From c787f0767f0597f7633635e9c424a37425fd775e Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Fri, 16 Jan 2026 14:00:06 +0000
Subject: [PATCH 5/7] Implement mix and mixp

---
 lib/glug.rb                        |  1 +
 lib/glug/chroma_extensions.rb      | 19 +++++++++++++++++++
 lib/glug/extensions.rb             | 12 ++++++------
 lib/glug/hsluv_modifiers.rb        | 20 ++++++++++++++++++++
 spec/fixtures/color_functions.glug |  8 ++++++++
 spec/fixtures/color_functions.json | 14 ++++++++++++++
 6 files changed, 68 insertions(+), 6 deletions(-)
 create mode 100644 lib/glug/chroma_extensions.rb

diff --git a/lib/glug.rb b/lib/glug.rb
index 58c8b28..54e7fd3 100644
--- a/lib/glug.rb
+++ b/lib/glug.rb
@@ -11,5 +11,6 @@ module Glug # :nodoc:
 require_relative 'glug/layer'
 require_relative 'glug/extensions'
 require_relative 'glug/hsluv_modifiers'
+require_relative 'glug/chroma_extensions'
 require_relative 'glug/stylesheet_dsl'
 require_relative 'glug/layer_dsl'
diff --git a/lib/glug/chroma_extensions.rb b/lib/glug/chroma_extensions.rb
new file mode 100644
index 0000000..0d82dd5
--- /dev/null
+++ b/lib/glug/chroma_extensions.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'chroma'
+require 'hsluv'
+
+module Chroma
+  class Color # :nodoc:
+    def mix(other, weight = 50)
+      other = other.paint if other.is_a?(String)
+      p = weight / 100.0
+
+      r = (rgb.r * p + other.rgb.r * (1 - p)).round
+      g = (rgb.g * p + other.rgb.g * (1 - p)).round
+      b = (rgb.b * p + other.rgb.b * (1 - p)).round
+
+      Chroma.paint("rgb(#{r}, #{g}, #{b})")
+    end
+  end
+end
diff --git a/lib/glug/extensions.rb b/lib/glug/extensions.rb
index bd82e8b..4a502e5 100644
--- a/lib/glug/extensions.rb
+++ b/lib/glug/extensions.rb
@@ -5,20 +5,20 @@
 
 # Colour methods on Integer
 class Integer
-  # rubocop:disable Style/StringConcatenation, Naming/MethodParameterName
-  def chroma_hex(op, p = nil)
+  # rubocop:disable Style/StringConcatenation
+  def chroma_hex(op, *args)
     color = ('#' + to_s(16).rjust(6, '0')).paint
-    (p.nil? ? color.send(op) : color.send(op, p)).to_hex
+    color.send(op, *args).to_hex
   end
 
-  def chroma(op, p = nil)
-    chroma_hex(op, p).gsub('#', '0x').to_i(16)
+  def chroma(op, *args)
+    chroma_hex(op, *args).gsub('#', '0x').to_i(16)
   end
 
   def to_hex_color
     '#' + to_s(16).rjust(6, '0')
   end
-  # rubocop:enable Style/StringConcatenation, Naming/MethodParameterName
+  # rubocop:enable Style/StringConcatenation
 end
 
 # Top-level colour generators
diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index 0db95e5..94f948f 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -47,5 +47,25 @@ def spinp(amount = 0)
       rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(new_h, s, l))
       Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
+
+    def mixp(other, weight = 50)
+      other = other.paint if other.is_a?(String)
+      p = weight / 100.0
+
+      h1, s1, l1 = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+      h2, s2, l2 = Hsluv.rgb_to_hsluv(other.rgb.r / 255.0, other.rgb.g / 255.0, other.rgb.b / 255.0)
+
+      # Interpolate hue on the shortest path around the color wheel
+      h_diff = h2 - h1
+      h_diff -= 360 if h_diff > 180
+      h_diff += 360 if h_diff < -180
+      new_h = (h1 + h_diff * (1 - p)) % 360
+
+      new_s = s1 * p + s2 * (1 - p)
+      new_l = l1 * p + l2 * (1 - p)
+
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(new_h, new_s, new_l))
+      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+    end
   end
 end
diff --git a/spec/fixtures/color_functions.glug b/spec/fixtures/color_functions.glug
index 32a833e..8cce2bc 100644
--- a/spec/fixtures/color_functions.glug
+++ b/spec/fixtures/color_functions.glug
@@ -49,3 +49,11 @@ end
 layer(:spinp, source: :shortbread) do
   line_color 0x998877.chroma(:spinp, 20)
 end
+
+layer(:mix, source: :shortbread) do
+  line_color 0x998877.chroma(:mix, '#ffffff', 50)
+end
+
+layer(:mixp, source: :shortbread) do
+  line_color 0x998877.chroma(:mixp, '#ffffff', 50)
+end
diff --git a/spec/fixtures/color_functions.json b/spec/fixtures/color_functions.json
index 17ddd60..a10ab55 100644
--- a/spec/fixtures/color_functions.json
+++ b/spec/fixtures/color_functions.json
@@ -91,6 +91,20 @@
       "id":"spinp",
       "source-layer":"spinp",
       "type":"line"
+    },
+    {
+      "paint":{"line-color":"#ccc4bb"},
+      "source":"shortbread",
+      "id":"mix",
+      "source-layer":"mix",
+      "type":"line"
+    },
+    {
+      "paint":{"line-color":"#cdc1be"},
+      "source":"shortbread",
+      "id":"mixp",
+      "source-layer":"mixp",
+      "type":"line"
     }
   ]
 }

From 71d7f4eda24c61cba0f72127218e5462859bf138 Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Fri, 16 Jan 2026 16:15:11 +0000
Subject: [PATCH 6/7] Refactor hsluv colour conversions to use helpers, for
 clarity

---
 lib/glug/hsluv_modifiers.rb | 59 +++++++++++++++++++------------------
 1 file changed, 30 insertions(+), 29 deletions(-)

diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index 94f948f..5008c66 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -7,64 +7,65 @@ module Chroma
   # Add hsluv versions of the color functions to chroma
   class Color
     def darkenp(amount = 10)
-      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      new_l = [l - amount, 0].max
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, new_l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, s, l = to_hsluv
+      l = [l - amount, 0].max
+      from_hsluv(h, s, l)
     end
 
     def lightenp(amount = 10)
-      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      new_l = [l + amount, 100].min
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, new_l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, s, l = to_hsluv
+      l = [l + amount, 100].min
+      from_hsluv(h, s, l)
     end
 
     def saturatep(amount = 10)
-      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      new_s = [s + amount, 100].min
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, new_s, l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, s, l = to_hsluv
+      s = [s + amount, 100].min
+      from_hsluv(h, s, l)
     end
 
     def desaturatep(amount = 10)
-      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      new_s = [s - amount, 0].max
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, new_s, l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, s, l = to_hsluv
+      s = [s - amount, 0].max
+      from_hsluv(h, s, l)
     end
 
     def greyscalep
-      h, _s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, 0, l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, _s, l = to_hsluv
+      from_hsluv(h, 0, l)
     end
     alias grayscalep greyscalep
 
     def spinp(amount = 0)
-      h, s, l = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      new_h = (h + amount) % 360
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(new_h, s, l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      h, s, l = to_hsluv
+      h = (h + amount) % 360
+      from_hsluv(h, s, l)
     end
 
     def mixp(other, weight = 50)
       other = other.paint if other.is_a?(String)
       p = weight / 100.0
 
-      h1, s1, l1 = Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
-      h2, s2, l2 = Hsluv.rgb_to_hsluv(other.rgb.r / 255.0, other.rgb.g / 255.0, other.rgb.b / 255.0)
+      h1, s1, l1 = to_hsluv
+      h2, s2, l2 = other.to_hsluv
 
       # Interpolate hue on the shortest path around the color wheel
       h_diff = h2 - h1
       h_diff -= 360 if h_diff > 180
       h_diff += 360 if h_diff < -180
-      new_h = (h1 + h_diff * (1 - p)) % 360
+      h = (h1 + h_diff * (1 - p)) % 360
+      s = s1 * p + s2 * (1 - p)
+      l = l1 * p + l2 * (1 - p)
+
+      from_hsluv(h, s, l)
+    end
 
-      new_s = s1 * p + s2 * (1 - p)
-      new_l = l1 * p + l2 * (1 - p)
+    def to_hsluv
+      Hsluv.rgb_to_hsluv(rgb.r / 255.0, rgb.g / 255.0, rgb.b / 255.0)
+    end
 
-      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(new_h, new_s, new_l))
+    def from_hsluv(h, s, l) # rubocop:disable Naming/MethodParameterName
+      rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, l))
       Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
   end

From 8381834af49c25f824163874ff20bfaf040da50a Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Thu, 22 Jan 2026 13:35:19 +0000
Subject: [PATCH 7/7] Pass mutable strings to Chroma

Chroma currently expects all strings to be mutable.

Calling this from frozen_string_literal files works fine, but not
on ruby 2.7 where things were handled differently. This syntax
can be removed when either a) Chroma accepts frozen strings or
b) ruby 2.7 support is dropped
---
 lib/glug/chroma_extensions.rb | 2 +-
 lib/glug/hsluv_modifiers.rb   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/glug/chroma_extensions.rb b/lib/glug/chroma_extensions.rb
index 0d82dd5..56905a8 100644
--- a/lib/glug/chroma_extensions.rb
+++ b/lib/glug/chroma_extensions.rb
@@ -13,7 +13,7 @@ def mix(other, weight = 50)
       g = (rgb.g * p + other.rgb.g * (1 - p)).round
       b = (rgb.b * p + other.rgb.b * (1 - p)).round
 
-      Chroma.paint("rgb(#{r}, #{g}, #{b})")
+      Chroma.paint(+"rgb(#{r}, #{g}, #{b})")
     end
   end
 end
diff --git a/lib/glug/hsluv_modifiers.rb b/lib/glug/hsluv_modifiers.rb
index 5008c66..0bc1683 100644
--- a/lib/glug/hsluv_modifiers.rb
+++ b/lib/glug/hsluv_modifiers.rb
@@ -66,7 +66,7 @@ def to_hsluv
 
     def from_hsluv(h, s, l) # rubocop:disable Naming/MethodParameterName
       rgb_values = Hsluv.rgb_prepare(Hsluv.hsluv_to_rgb(h, s, l))
-      Chroma.paint("rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
+      Chroma.paint(+"rgb(#{rgb_values[0]}, #{rgb_values[1]}, #{rgb_values[2]})")
     end
   end
 end