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Image render optimization question

Added by Tom Puckett over 10 years ago

I would like to understand how to get the fastest possible effective frame rate when performing continuous image updates as described below. There is some network traffic that seems unnecessary and I wonder if I can get Wt to avoid it.

During session initialization:

mpTheImage = new WImage(WLink(), "alternate text", root());

mpTheImage->setId("IMIImage");

...

mpTheImage->imageLoaded().connect(this, &ImageDisplayApp::HandleImageRequest);


The handler ImageDisplayApp::HandleImageRequest() renders the next frame's pixels and then:

WLink vLink.setResource(mpImageResource); // mpImageResource points to a WMemoryResource in heap

mpTheImage->setImageLink(vLink);

mpTheImage->refresh();


After the first frame is rendered, I see on the network that the onload event causes a POST command from the browser, a server response, and then a GET for the image resource. This means 2 round trips for each frame. Can this be avoided, perhaps by getting the imageLoaded event to issue a GET directly, or maybe a POST for the image resource directly without an intermediate step?

If standard Wt steps can't do this, do you have support for sockets so I could implement my own streamlined protocol?

Thanks for helping.


Replies (1)

RE: Image render optimization question - Added by Koen Deforche over 10 years ago

Hey,

You have two options:

1) you can connect a JavaScript function to the imageLoaded() signal, which immediately updates the URL.

e.g.:

mpTheImage->imageLoaded().connect("function(o) { o.src='next.png'; }");

2) you can base64-encode the image in the URL

e.g.

vLink.setUrl('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA
AAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO
9TXL0Y4OHwAAAABJRU5ErkJggg==');

Wt has a utility function to perform such base64-encoding: Wt::Utils::base64Encode()

Note that in older (mostly IE) browsers there are limitations to the size of the URL.

Regards,

koen

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