basic image thumbnails

app/models/outfit.rb

@@ -14,6 +14,8 @@ class Outfit < ActiveRecord::Base
   scope :wardrobe_order, order('starred DESC', :name)
   
   mount_uploader :image, OutfitImageUploader
+  
+  after_commit :enqueue_image!
 
   def as_json(more_options={})
     serializable_hash :only => [:id, :name, :pet_state_id, :starred],
@@ -68,23 +70,35 @@ class Outfit < ActiveRecord::Base
   end
   
   # Returns the array of SwfAssets representing each layer of the output image,
-  # ordered from bottom to top.
-  def layered_assets
-    visible_assets.sort { |a, b| a.zone.depth <=> b.zone.depth }
+  # ordered from bottom to top. Careful: this method is memoized, so if the
+  # image layers change after its first call we'll get bad results.
+  def image_layers
+    @image_layers ||= visible_assets_with_images.sort { |a, b| a.zone.depth <=> b.zone.depth }
   end
   
-  # Creates and writes the thumbnail images for this outfit. (Writes to file in
-  # development, S3 in production.) Runs #save! on the record, so any other
-  # changes will also be saved.
+  # Creates and writes the thumbnail images for this outfit iff the new image
+  # would be different than the current one. (Writes to file in development,
+  # S3 in production.) If the image is updated, updates the image layers hash
+  # and runs #save! on the record, so any other changes will also be saved.
   def write_image!
-    Tempfile.open(['outfit_image', '.png']) do |image|
-      create_image! image
-      self.image = image
-      save!
+    if image_layers_dirty?
+      Tempfile.open(['outfit_image', '.png']) do |image|
+        create_image! image
+        self.image_layers_hash = generate_image_layers_hash
+        self.image = image
+        save!
+      end
     end
+    
     self.image
   end
   
+  # Enqueue an image write iff the new image would be different than the
+  # current one.
+  def enqueue_image!
+    Resque.enqueue(OutfitImageUpdate, id) if image_layers_dirty?
+  end
+  
   def s3_key(size)
     URI.encode("#{id}/#{size.join 'x'}.png")
   end
@@ -108,13 +122,13 @@ class Outfit < ActiveRecord::Base
   # Creates a 600x600 PNG image of this outfit, writing to the given output
   # file.
   def create_image!(output)
-    layers = self.layered_assets
-    base_layer = layers.shift
+    base_layer = image_layers.first
+    above_layers = image_layers[1..-1]
     write_temp_swf_asset_image! base_layer, output
     output.close
 
     Tempfile.open(['outfit_overlay', '.png']) do |overlay|
-      layers.each do |layer|
+      above_layers.each do |layer|
         overlay.open
         write_temp_swf_asset_image! layer, overlay
         overlay.close
@@ -151,6 +165,21 @@ class Outfit < ActiveRecord::Base
     all_assets.select { |a| (1 << (a.zone_id - 1)) & restricted_zones_mask == 0 }
   end
   
+  def visible_assets_with_images
+    visible_assets.select(&:has_image?)
+  end
+  
+  # Generate 8-char hex digest representing visible image layers for this outfit.
+  # Hash function should be decently collision-resistant.
+  def generate_image_layers_hash
+    @generated_image_layers_hash ||=
+      Digest::MD5.hexdigest(image_layers.map(&:id).join(',')).first(8)
+  end
+  
+  def image_layers_dirty?
+    generate_image_layers_hash != self.image_layers_hash
+  end
+  
   IMAGE_BASE_SIZE = [600, 600]
   def write_temp_swf_asset_image!(swf_asset, file)
     key = swf_asset.s3_key(IMAGE_BASE_SIZE)

app/models/outfit_image_update.rb

@@ -0,0 +1,8 @@
+class OutfitImageUpdate
+  @queue = :outfit_image_updates
+
+  def self.perform(id)
+    Outfit.find(id).write_image!
+  end
+end
+

config/initializers/carrierwave.rb

@@ -3,7 +3,7 @@
 # this to use S3 on all environments for those images only.)
 
 CarrierWave.configure do |config|
-  if Rails.env.production? || true # REMOVE
+  if Rails.env.production?
     s3_config = YAML.load_file Rails.root.join('config', 'aws_s3.yml')
     access_key_id = s3_config['access_key_id']
     secret_access_key = s3_config['secret_access_key']

db/migrate/20120716193946_add_image_layers_hash_to_outfit.rb

@@ -0,0 +1,9 @@
+class AddImageLayersHashToOutfit < ActiveRecord::Migration
+  def self.up
+    add_column :outfits, :image_layers_hash, :string, :length => 8
+  end
+
+  def self.down
+    remove_column :outfits, :image_layers_hash
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20120521164652) do
+ActiveRecord::Schema.define(:version => 20120716193946) do
 
   create_table "auth_servers", :force => true do |t|
     t.string "short_name", :limit => 10,       :null => false
@@ -116,8 +116,9 @@ ActiveRecord::Schema.define(:version => 20120521164652) do
     t.datetime "created_at"
     t.datetime "updated_at"
     t.string   "name"
-    t.boolean  "starred",      :default => false, :null => false
+    t.boolean  "starred",           :default => false, :null => false
     t.string   "image"
+    t.string   "image_layers_hash"
   end
 
   add_index "outfits", ["pet_state_id"], :name => "index_outfits_on_pet_state_id"

public/outfits/.gitignore

@@ -0,0 +1,2 @@
+*
+!.gitignore