在 Haskell 个图表中加载外部图像

Question

所以我有这个疑问。我已经有了处理本地（嵌入式）图像文件的代码，但现在我需要加载外部图像。用 loadImageExt 替换无用：

productImageIO :: IO (Diagram B)
productImageIO = do
  res <- loadImageExt "https://s7d2.scene7.com/is/image/dkscdn/16JDNMJRDNCLPSBLKJRD_Black_Black_White_is/"
  return $
    case res of
      Left err -> mempty
      Right product -> image product



• No instance for (Renderable (DImage Double External) B)
        arising from a use of ‘image’
    • In the expression: image product
      In a case alternative: Right product -> image product
      In the second argument of ‘($)’, namely
        ‘case res of
           Left err -> mempty
           Right product -> image product’
   |
26 |       Right product -> image product
   |                        ^^^^^^^^^^^^^

查看 loadImageExt and readImage 的源代码，我看不到它实际执行 http 内容以获取图像的位置。

文档说，loadImageExt，检查文件是否存在，并使用 JuicyPixels 计算出正确的大小，但保存对图像的引用而不是光栅数据

所以请原谅我的无知，但这是否意味着我需要在这种情况下添加http加载逻辑？或者我只是遗漏了一些要点来完成这项工作？

UPD：我可能错了，有一些快速简便的方法可以通过放置 link 来加载外部图像，但对我有用的是使用 http-conduit，在 ByteString 中获取响应并解析它：

productImageIO :: String -> IO (Diagram B)
productImageIO path = do
   response <- fmap getResponseBody $ parseRequest path >>= httpBS
   return $
     case loadImageEmbBS response of
        Left error -> mempty
        Right decodedImage -> image decodedImage

它甚至可以加载 https 图片，像这样 https://sneakernews.com/wp-content/uploads/2018/01/jordan-russell-westbrook-signature-shoe-creamsicle-3.jpg?w=1140

Answer 1

loadImageExt appears to expect a FilePath, not a URL, but that's not what the compiler is complaining about. It is complaining that the particular image returned, a DImage Double External, is not Renderable. This could be because the renderer in use doesn't understand external images; for instance, Diagrams.Backend.SVG appears to support Embedded but not External. In contrast, Diagrams.Backend.Html5 supports External but not Embedded. At a guess, it's expected that your diagram refers using local filenames to images, not cross-site URLs. It could be that you can inject URLs with uncheckedImageRef, but still only if the backend supports External. The Diagrams manual section on images 声称只有 Cairo 后端会这样做，但这可能不准确。

在 Haskell 个图表中加载外部图像

Load external image in Haskell Diagrams

haskell

external

haskell-diagrams