I am currently trying to program an online drawing program using the HTML5 canvas.
The thing is, I need to have the current canvas saved somewhere globally. Static variables work, but they do not get shared across a Webgarden. This results in two different drawings being created.
I will have to somehow create a new application object which is shared. I figured I will need an external application holding them.
1) How do I replace the application object with my own?
So either I will have to make my own program and call to it with remoting or use the ASP.NET session state server for application variables. I favor the Session State Server though.
2) How do I use the session state server for my own variables? How do I access it?
I searched high and low on the internet and only found the ideas mentioned above, but no help executing them.
I mainly code in VB.NET, but I can also understand C# code for examples.
A little info on my application:
The client side has two canvas objects on top of each other. The top canvas object us used for drawing stuff, the canvas object below it holds the drawing in the end.
When something is drawn, it is sent to the server in it’s base64 representation. (getDataUri)
The server puts this graphic on top of a stored Bitmap object through a Graphics object.
How the changes are being distributed to the other clients, I am working on that right now. Either I transfer the complete picture or each and every change that is submitted. This should work through Server Push. If this does not work thoroughly I will have to save and timestamp changes.
A link to the current implementation, which is not currently fetching changes (but they get transfered to the server… With the problem that some reach one instance some reach the other on either w3wp in the webgarden) from the server is here: http://anno.sinni800.ath.cx/Canvas/Collab
Another option is to use a distributed cache such as memcached.
Memcached for Windows
Using Memchached with asp.net