refactor(watermark): small text based watermarked to increase document visibility

app/jobs/titre_identite_watermark_job.rb

@@ -10,77 +10,18 @@ class TitreIdentiteWatermarkJob < ApplicationJob
   # (to avoid modifying the file while it is being scanned).
   retry_on FileNotScannedYetError, wait: :exponentially_longer, attempts: 10
 
-  MAX_IMAGE_SIZE = 1500
-  SCALE = 0.9
-  WATERMARK = URI.parse(WATERMARK_FILE).is_a?(URI::HTTP) ? WATERMARK_FILE : Rails.root.join("app/assets/images/#{WATERMARK_FILE}")
-
   def perform(blob)
     return if blob.watermark_done?
     raise FileNotScannedYetError if blob.virus_scanner.pending?
 
     blob.open do |file|
-      watermark = resize_watermark(file)
-
-      if watermark.present?
-        processed = watermark_image(file, watermark)
+      Tempfile.create(["watermarked", File.extname(file)]) do |output|
+        processed = WatermarkService.new.process(file, output)
+        return if processed.blank?
 
         blob.upload(processed)
         blob.touch(:watermarked_at)
       end
     end
   end
-
-  private
-
-  def watermark_image(file, watermark)
-    ImageProcessing::MiniMagick
-      .source(file)
-      .convert("png")
-      .resize_to_limit(MAX_IMAGE_SIZE, MAX_IMAGE_SIZE)
-      .composite(watermark, mode: "over", gravity: "center")
-      .call
-  end
-
-  def resize_watermark(file)
-    metadata = image_metadata(file)
-
-    if metadata[:width].present? && metadata[:height].present?
-      width = [metadata[:width], MAX_IMAGE_SIZE].min * SCALE
-      height = [metadata[:height], MAX_IMAGE_SIZE].min * SCALE
-      diagonal = Math.sqrt(height**2 + width**2)
-      angle = Math.asin(height / diagonal) * 180 / Math::PI
-
-      ImageProcessing::MiniMagick
-        .source(WATERMARK)
-        .resize_to_limit(diagonal, diagonal / 2)
-        .rotate(-angle, background: :transparent)
-        .call
-    end
-  end
-
-  def image_metadata(file)
-    read_image(file) do |image|
-      if rotated_image?(image)
-        { width: image.height, height: image.width }
-      else
-        { width: image.width, height: image.height }
-      end
-    end
-  end
-
-  def read_image(file)
-    require "mini_magick"
-    image = MiniMagick::Image.new(file.path)
-
-    if image.valid?
-      yield image
-    else
-      logger.info "Skipping image analysis because ImageMagick doesn't support the file"
-      {}
-    end
-  end
-
-  def rotated_image?(image)
-    ['RightTop', 'LeftBottom'].include?(image["%[orientation]"])
-  end
 end

app/services/watermark_service.rb

@@ -0,0 +1,118 @@
+class WatermarkService
+  POINTSIZE = 20
+  KERNING = 1.2
+  ANGLE = 45
+  FILL_COLOR = "rgba(0,0,0,0.4)"
+
+  attr_reader :text
+  attr_reader :text_length
+
+  def initialize(text = APPLICATION_NAME)
+    @text = " #{text} " # give more space around each occurence
+    @text_length = @text.length
+  end
+
+  def process(file, output)
+    metadata = image_metadata(file)
+
+    return if metadata.blank?
+
+    watermark_image(file, output, metadata)
+
+    output
+  end
+
+  private
+
+  def watermark_image(file, output, metadata)
+    MiniMagick::Tool::Convert.new do |convert|
+      setup_conversion_commands(convert, file)
+      apply_watermark(convert, metadata)
+      convert << output.to_path
+    end
+  end
+
+  def setup_conversion_commands(convert, file)
+    convert << file.to_path
+    convert << "-pointsize"
+    convert << POINTSIZE
+    convert << "-kerning"
+    convert << KERNING
+    convert << "-fill"
+    convert << FILL_COLOR
+    convert << "-gravity"
+    convert << "northwest"
+  end
+
+  # Parcourt l'image ligne par ligne et colonne par colonne en y apposant un filigrane
+  # en alternant un décalage horizontal sur chaque ligne
+  def apply_watermark(convert, metadata)
+    stride_x, stride_y, initial_offsets_x, initial_offset_y = calculate_watermark_params
+
+    0.step(by: stride_y, to: metadata[:height] + stride_y * 2).with_index do |offset_y, index|
+      initial_offset_x = initial_offsets_x[index % 2]
+
+      0.step(by: stride_x, to: metadata[:width] + stride_x * 2) do |offset_x|
+        x = initial_offset_x + offset_x
+        y = initial_offset_y + offset_y
+        draw_text(convert, x, y)
+      end
+    end
+  end
+
+  def calculate_watermark_params
+    # Approximation de la longueur du texte, qui marche bien pour les constantes par défaut
+    char_width_approx = POINTSIZE / 2
+    char_height_approx = POINTSIZE * 3 / 4
+
+    # Dimensions du rectangle de texte
+    text_width_approx = char_width_approx * text_length * Math.cos(ANGLE * (Math::PI / 180)).abs
+    text_height_approx = char_width_approx * text_length * Math.sin(ANGLE * (Math::PI / 180)).abs + char_height_approx
+    diagonal_length = Math.sqrt(text_width_approx**2 + text_height_approx**2)
+
+    # Calcul des décalages entre chaque colonne et ligne
+    # afin que chaque occurence "suive" la précédente
+    stride_x = ((diagonal_length + char_width_approx) / Math.cos(ANGLE * (Math::PI / 180)))
+    stride_y = text_height_approx
+
+    initial_offsets_x = [0, (0 - stride_x / 2).round] # Motif de damier en alternant le décalage horizontal
+    initial_offset_y = 0 - stride_y # Offset négatif pour mieux couvrir le nord ouest
+
+    [stride_x.round, stride_y.round, initial_offsets_x, initial_offset_y.round]
+  end
+
+  def draw_text(convert, x, y)
+    # A chaque insertion de texte, positionne le curseur, définit la rotation, puis réinitialise ces paramètres pour la prochaine occurence
+    # Note: x and y can be negative value
+    convert << "-draw"
+    convert << "translate #{x},#{y} rotate #{-ANGLE} text 0,0 '#{text}' rotate #{ANGLE} translate #{-x},#{-y}"
+  end
+
+  def image_metadata(file)
+    read_image(file) do |image|
+      width = image.width
+      height = image.height
+
+      if rotated_image?(image)
+        width, height = height, width
+      end
+
+      { width: width, height: height }
+    end
+  end
+
+  def read_image(file)
+    image = MiniMagick::Image.new(file.to_path)
+
+    if image.valid?
+      yield image
+    else
+      Rails.logger.info "Skipping image analysis because ImageMagick doesn't support the file #{file}"
+      nil
+    end
+  end
+
+  def rotated_image?(image)
+    ['RightTop', 'LeftBottom'].include?(image["%[orientation]"])
+  end
+end

config/env.example.optional

@@ -68,9 +68,6 @@ DS_ENV="staging"
 # Instance customization: PDF export logo ---> to be put in "app/assets/images"
 # DOSSIER_PDF_EXPORT_LOGO_SRC="app/assets/images/header/logo-ds-wide.png"
 
-# Instance customization: watermark for identity documents
-# WATERMARK_FILE=""
-
 # Enabling maintenance mode
 # MAINTENANCE_MODE="true"
 

config/initializers/watermark.rb

@@ -1 +0,0 @@
-WATERMARK_FILE = ENV.fetch('WATERMARK_FILE', 'watermark.png')

lib/tasks/pjs.rake

@@ -22,4 +22,32 @@ namespace :pjs do
 
     blobs.in_batches { |batch| batch.ids.each { |id| PjsMigrationJob.perform_later(id) } }
   end
+
+  desc "Watermark demo. Usage: noglob rake pjs:watermark_demo[tmp/carte-identite-demo-1.jpg]"
+  task :watermark_demo, [:file_path] => :environment do |_t, args|
+    file = Pathname.new(args[:file_path])
+    output_file = Rails.root.join('tmp', "#{file.basename(file.extname)}_watermarked#{file.extname}")
+
+    processed = WatermarkService.new.process(file, output_file)
+
+    if processed
+      rake_puts "Watermarked: #{processed}"
+    else
+      rake_puts "File #{file} not watermarked. Read application log for more information"
+    end
+  end
+
+  desc "Watermark demo all defined demo files. Usage: noglob rake pjs:watermark_demo_all"
+  task :watermark_demo_all => :environment do
+    # You must have these filenames in tmp/ to run this demo (download ID cards specimens)
+    filenames = [
+      "carte-identite-demo-1.jpg", "carte-identite-demo-2.jpg", "carte-identite-demo-3.png", "carte-identite-demo-4.jpg",
+      "carte-identite-demo-5.jpg", "passeport-1.jpg", "passeport-2.jpg"
+    ]
+
+    filenames.each do |file|
+      Rake::Task["pjs:watermark_demo"].invoke("tmp/#{file}")
+      Rake::Task["pjs:watermark_demo"].reenable
+    end
+  end
 end

spec/services/watermark_service_spec.rb

@@ -0,0 +1,23 @@
+RSpec.describe WatermarkService do
+  let(:image) { file_fixture("logo_test_procedure.png") }
+  let(:watermark_service) { WatermarkService.new }
+
+  describe '#process' do
+    it 'returns a tempfile if watermarking succeeds' do
+      Tempfile.create do |output|
+        watermark_service.process(image, output)
+        # output size should always be a little greater than input size
+        expect(output.size).to be_between(image.size, image.size * 1.5)
+      end
+    end
+
+    it 'returns nil if metadata is blank' do
+      allow(watermark_service).to receive(:image_metadata).and_return(nil)
+
+      Tempfile.create do |output|
+        expect(watermark_service.process(image.to_path, output)).to be_nil
+        expect(output.size).to eq(0)
+      end
+    end
+  end
+end