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#Jun 17th, 2008 @ 1:11 PM
alexmac
alexmac
Hi,
Is there a way to save a Silverlight canvas to disk or to retrieve the XAML of the current canvas after you have programmatically added objects?

I have a diagram users can annotate and need to save it as Jpg, PNG or GIF.

I found this link below that implies you can do this with an InkPresenter but is there a another better way?:
http://www.thedatafarm.com/blog/2008/01/31/ConvertingSilverlightInkPresenterImagesToAPNGFile.aspx

Thanks,

Alex
#Jun 17th, 2008 @ 2:40 PM
stevo_
stevo_
Human after all

I would imagine theres an object that lets you render any visual object into a buffer.. this should give you a bitmap you could probably encode to jpeg or something..

#Jun 18th, 2008 @ 12:40 PM
alexmac
alexmac
Right! Have finally got this working.

Sadly cant use the method suggested in figuerres link as for security reasons in Silverlight they have disabled some of those functions. I have managed to get the first method working (http://www.thedatafarm.com/blog/2008/01/31/ConvertingSilverlightInkPresenterImagesToAPNGFile.aspx)

Basically you have to use an InkPresenter this allows you to easily get a collection of the strokes (although you could probably do the same with Canvas and iterate through the objects)
Iterate through the strokes in the InkPresenter and convert the objects into XAML
Send this to a web service
The web service has full access to the WPF toolset so you can then convert it into a png etc

Ill post some example code once I have tidied it up.
#Jun 18th, 2008 @ 2:33 PM
figuerres
figuerres
???
Question:  what did not allow it to work??  the file I/O I can see as an issue but the basic steps to get an in-memory bitmap should work.
#Jun 19th, 2008 @ 1:33 AM
stevo_
stevo_
Human after all

Because the RenderTargetBitmap (which allows you to render a visual as a bitmap), is marked as security critical in silverlight.. which means that transparent (user) code cannot directly call it.

Shame, but as you've found- theres somewhat of a workaround.. even if its pretty bizare!

#Jun 19th, 2008 @ 5:22 AM
alexmac
alexmac
Yep stevo_ is right.

I am currently have issues getting Silverlight to talk to my web service but havent really looked into it properly yet. Keep getting a 404 message when try and call it which is weird as I can browse to it and a windows forms app can talk to it.
#Jun 20th, 2008 @ 10:52 AM
alexmac
alexmac
Okay sample code at:
http://www.devcafe.co.uk/downloads/createImage.zip

Its all messy as I am still playing with it.

This is basically the sample code at http://www.thedatafarm.com/blog/2008/01/31/ConvertingSilverlightInkPresenterImagesToAPNGFile.aspx put together for Silverlight beta 2.

Problems I found
You need to increase the size of the received string in the config file ofyour WCF service as the default will be way too small to accept the incoming XML
Jpg seems to encode with a black background but gif and png dont (?)
If you run this in the debugger using the inbuilt webserver it wont work. I think this is something to do with cross domain access. Apparently you can resolve this with clientaccesspolicy.xml or theres another one called crossdomain.xml but I couldnt get this to work.
#Jun 20th, 2008 @ 11:53 AM
stevo_
stevo_
Human after all

gif and png support transparency, jpeg doesn't.. so the jpeg has to have a background colour.. the default is probably black.. you can change this to whatever you require.

and you'll get various issues using the built in dev host.. if you have iis, you can configure the project to launch the iis site and attach a debugger to it.

#Aug 1st, 2008 @ 4:07 PM
mskaditya
mskaditya
I have a simialr problem, where I have a canvas and i have multipe Image place holders in it. User has an option to change the contents of the Image place holders and I need to save the over lapping pictue that is created. any help on this...

thanks in advacne
#Aug 4th, 2008 @ 12:34 AM
alexmac
alexmac
Mskaditya I think the only way to do this at present is to iterate through the objects that are on the canvas, send it to a web service then reconstruct it using the full WPF feature set. You will need to send the positioning, image selected and z index then you can use standard GDI functions to render the final image.
#Aug 17th, 2008 @ 5:38 AM
mskaditya
mskaditya
thanks for the reply alex.


This seems to be lot of work, as I will have multiple images.

I have one question and one ask.

1. can i make a silverlight canvas a WPF canvas, I mean by passing the XAML string. since WPF also works based on this, is possible or doable.

the ask is, alex I did not understand what you mean by passing the image to a webservice, can you throw somelight on it please. pseudo or sample code will be of great help.

#Aug 17th, 2008 @ 8:56 AM
alexmac
alexmac

Hi mskaditya,
Yes I believe it would be possible to translate a silverlight canvas to a WPF canvas. I dont think at the moment you can just try something like myCanvas.xaml  through. Thus the approach I took (based on one of the articles referenced above) was to iterate through the child objects of the canvas and create the xaml.

You can download my code from http://www.devevening.co.uk/downloads/Silverlight101.zip  (there is some other stuff in here such as a presentation and basic examples).  This code only iterates through the stroke collection so you will need to figure out the xaml for your images etc.

Silverlight can not do everything that WPF can do (it would be too big for a browser download and it wouldnt work on every platform), thus you need to send the xaml data via a web service to process it.

I suggest what you need to do is:

Iterate through images on canvas
Create a string builder object with the xaml for each image in
Send this xaml to a webservice
Process the incoming xaml and use WPF file save methods as in my example

Alex

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