如何为水印图像创建一个重要的 ActiveStorage 变体？

Question

我编写了以下 ImageMagick 命令，它获取水印图像、对其进行缩放并将其合成到基础图像上、平铺：

convert image.png \( watermark.png -resize 5% -write mpr:watermark +delete \) \( +clone -tile mpr:watermark -draw "color 0,0 reset" \)  -compose over -composite watermarked_image.png

我想将其定义为 Active Storage 变体，这样我就可以在某些情况下为图像添加水印，但我做空了。我只能找到非常简单的转换示例。这可能作为 Active Storage 变体吗？

Answer 1

我终于弄明白了，想分享答案以防其他人在这里寻求帮助。我找到 the following article, which explains the basic premise. From there it was only a matter of translating the ImageMagick command into the correct MiniMagick API 个调用。

require "image_processing"

module ImageProcessing
  module MiniMagick
    module Processing
      extend ActiveSupport::Concern

      included do
        def watermark(scale: 0.5, opacity: 0.5)
          watermark_path = Rails.root.join('lib', 'watermark.png')
          formatted_scale = "%0.0f%%" % [scale* 100]

          magick.stack do |stack|
            stack << watermark_path

            stack.alpha('on')
            stack.channel('a')
            stack.evaluate('multiply', opacity.to_f)
            stack.channel.+

            stack.resize(formatted_scale)
            stack.write('mpr:watermark')
            stack.delete.+
          end

          magick.stack do |stack|
            stack.clone.+
            stack.tile('mpr:watermark')
            stack.draw('color 0,0 reset')
          end

          magick.compose('over')
          magick.composite
        end
      end
    end
  end
end

ImageProcessing::MiniMagick::Processor.include(
  ImageProcessing::MiniMagick::Processing
)

然后，假设您有一个带有 image 附件的模型，只需使用以下命令调用新的水印变体：

design.image.variant(
  watermark: { scale: 0.25, opacity: 0.2 },
)

如何为水印图像创建一个重要的 ActiveStorage 变体？

How do I create a non-trivial ActiveStorage variant for watermarking images?

ruby-on-rails

rails-activestorage