Add a way to consistently get the same image

It would be nice if there was a way to make a request using a stable URL and always get the same image back for that request.

One simple option

I have seen some placeholder services that will always return the same image for a given size. For example, service/300x300, no matter how many times you request it or where from, it will always return the same image instead of a random image.

This option isn't great though, because frequently mockup pages will have multiple img tags of the same size, and would want different photos to populate them.

User-provided value option

The first thing I thought of would be to add another value, e.g. service/300x300/1, service/300x300/2, service/300x300/3315fa35180cz3. This number wouldn't really be an identifier. Instead, the service could take the extra value and make a hash of it, and somehow have a stable mapping of hash to image.

service/300x300 would still return a random image. But if a user wants to use a stable identifier and get a consistent image, they can provide any value after the size. (I don't know how difficult this would be with the API, though.)

The advantages is that a mockup could still have different images for different tags

<figure>
  <img src="http://spaceholder.cc/300x300/first-thing">
  <figcaption>First Thing</figcaption>
</figure>
<figure>
  <img src="http://spaceholder.cc/300x300/second-thing">
  <figcaption>Second Thing</figcaption>
</figure>
<figure>
  <img src="http://spaceholder.cc/300x300/third-thing">
  <figcaption>Third Thing</figcaption>
</figure>

Other options

I haven't thought this far, but there might be better ideas out there.

Simplistically, if you had 16 images instead of 11, you could do (pseudocode, I'm not real up on Ruby)

class Image
  def initialize(dimensions)
    @image = MiniMagick::Image.open(Dir.glob('./app/assets/images/photos/*.jpg').sample)
    @dimensions = dimensions
  end

  def initialize(dimensions, stableid)
    # get a hash that, given dimensions and stableid, is always the same.
    sha = sha1(dimensions.width + dimensions.height + stableid)

    # get the first character of the hash
    indexstring = substring(sha, 0, 1)

    # turn that first character into a number between 0 and 15
    index = hexToInt(indexstring)

    # this assumes you have exactly 16 images in the photos directory, though. Should be safe and check.
    @image = MiniMagick::Image.open(Dir.glob('./app/assets/images/photos/*.jpg')[index]) 
    @dimensions = dimensions
  end

I'm sure with more thinking, there would be a good way to turn a hash into an index for any size array.

jgarber623 / spaceholder.cc