RMagick to_blob display via AJAX call

Hi,

HELP!

This seems too simple - I MUST be overlooking something...

I can create an rmagick image in my controller and display it fine.

When I create a second image and try to refresh via observe_form, it
shows garbled text...

BTW: RMagick is wonderful.

I am having a difficulty in what seems very elementary in Rails.

1. Create a form that user enters some params (color)

2. Observe the form and create an image (to_blob)

3. Display the image on the same form (near real time). As the user
enter params it builds their image.

What it displays in the div (dynamic image) is...

�PNG IHDR $ �6 pHYsHHF�k>�IDATx���1 �@���C �) ˡKe� �7?�33 R�� � �d`$
I @�� �d`$ I @�� �d`$ I @�� �d`$ I @�� �d`$ I @�� �d`$ I @�� �d`$ I
@�� �d`$ I @�� �d`$��T 4 �W�IEND�B`�

This observe_field looks dodgy - you're telling it to replace the
contents of the results div with the data that comes back from the
server, but what comes back isn't html, its raw png data, which the
browser then attempts to display as html.

Fred

rigth and also

<%= image_tag url_for(:controller => “tabs”, :action
=> “watch_text”, :id => 0) %>

the image tag should poing to a path in the server and the image should be serve by the webserver not rails.

the controller you return a partial with a link to the path of the image in the server

right and also

<%= image_tag url_for(:controller => “tabs”, :action
=> “watch_text”, :id => 0) %>

the image tag should point to a path in the server and the image should be serve by the webserver not rails.

As long as the URL will return an image, it does not need to be an asset served by the webserver. In an old project, I had a SparklineController that could return the sparkline for a given set of parameters and it worked quite well.

However I do agree with Frederick’s comment about your observe_form.

-Rob

<%= observe_form 'entries', :frequency => 2.0,
  :update => :results,
  :url => { :action => :watch_text }
   %>

This observe_field looks dodgy - you’re telling it to replace the
contents of the results div with the data that comes back from the
server, but what comes back isn’t html, its raw png data, which the
browser then attempts to display as html.

Fred


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Rob Biedenharn

Rob@AgileConsultingLLC.com http://AgileConsultingLLC.com/

rab@GaslightSoftware.com http://GaslightSoftware.com/

Rob Biedenharn wrote:

right and also

<%= image_tag url_for(:controller => "tabs", :action
=> "watch_text", :id => 0) %>

the image tag should point to a path in the server and the image
should be serve by the webserver not rails.

As long as the URL will return an image, it does not need to be an
asset served by the webserver. In an old project, I had a
SparklineController that could return the sparkline for a given set of
parameters and it worked quite well.

However I do agree with Frederick's comment about your observe_form.

-Rob

> %>
Groups "Ruby on Rails: Talk" group.
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Rob Biedenharn
Rob@AgileConsultingLLC.com http://AgileConsultingLLC.com/
rab@GaslightSoftware.com http://GaslightSoftware.com/

What I "seem" to need to do (and this works) is to save the image as a
resoruce on disk, then call it as follows.

- delete previous image if it exists
- create a new image
- set (flash) the new image name
- render the new webserver source (to new image name - timestamped)
(I will add user_id, etc, later)

I still cannot see how to possibly pass a blob through ajax response, so
this is the my simple (NOT effective approach) versus memory storage.

def watch_text

        rec_color = params[:color]

        @color_img = Magick::Image.new(288, 36) {self.background_color =
rec_color }
        @color_img.format = 'png'
        if flash[:prev_fname]
          File.open("public/images/#{flash[:prev_fname]}")
          File.delete("public/images/#{flash[:prev_fname]}")
        end

        @ts = Time.now.to_i.to_s
        f_name = "tab_" + @ts + ".png"
        @color_img.write("public/images/#{f_name}")
        flash[:prev_fname] = f_name

       @mb2 = "/images/#{f_name}"
       render(:text => '<img alt="0" src="' + @mb2 + '" />' )

  end

I think the root of the problem you are grappling with is that putting
an image on a page requires two http requests: one that creates an
image tag with the appropriate src attribute, and then the request
from the browser when it tries to display that img tag.
If that isn't acceptable then there is a way of encoding the image
data in the img tag your self, you basically stick

<img src="data:image/bla,base64encodedimagedatahere" />

It's not supported by all browsers though ( http://en.wikipedia.org/wiki/Data_URI_scheme
)

Fred

can you explain why arent you using paperclip? i use it with imagemagick and can easily convert my file to almost any format with very easy.

can you explain why arent you using paperclip? i use it with imagemagick and can easily convert my file to almost any format with very easy.

Well, he’s not starting with a file, for one thing.

-Rob

I still cannot see how to possibly pass a blob through ajax response, so
this is the my simple (NOT effective approach) versus memory storage.

I think the root of the problem you are grappling with is that putting
an image on a page requires two http requests: one that creates an
image tag with the appropriate src attribute, and then the request
from the browser when it tries to display that img tag.
If that isn’t acceptable then there is a way of encoding the image
data in the img tag your self, you basically stick

It’s not supported by all browsers though ( http://en.wikipedia.org/wiki/Data_URI_scheme
)

Fred

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Rob Biedenharn

Rob@AgileConsultingLLC.com http://AgileConsultingLLC.com/

rab@GaslightSoftware.com http://GaslightSoftware.com/

Lol

Frederick Cheung wrote: