Question

The requirement is like this:

I must issue a command requesting a screenshot. The twist? The command specifies a time – and that time is in the PAST. Not forever, mind you, just within a 30 second window.

My command indicates the actual second, and the corresponding screenshot is pulled from the rolling cache and saved in a permanent location for another process.

To accomplish this, I must take a screenshot every second, and I must preserve them for 30 seconds. After that the cache can purge itself.

My question is

What method for screenshots is least impactful against the desktop?

Answer 1

I can’t imagine that one frame per second is going to be terrible for performance. Have you tried the simplest possible method to see if it impacts performance?

Take a look at http://www.dotnetjalps.com/2007/06/how-to-take-screenshot-in-c.html for information on how to get a screen shot.

I would suggest you use a timer:

var ssTimer = new System.Threading.Timer((s) =>
    {
      GetAndStoreScreenShot();
    }, null, 1000, 1000);

You’ll need some synchronization on your cache to prevent threading problems (i.e. trying to read the first item in the cache while it’s being pushed out). Probably easiest to use a lock, since that’s not going to be particularly performance sensitive.

As for what to use for a cache, I’d suggest a LinkedList. It’s easy to append to the list (AddLast()) and remove the first item (RemoveFirst()), and since you’ll only have 30 of them and requests for screen shots will be relatively infrequent, a sequential scan to get the nth item wouldn’t be too time consuming.

Or you can implement a simple circular buffer using List or Array. Increment an index to be the insertion spot, wrapping around when you increment off the end. A lookup then becomes a simple matter of modulo arithmetic.