VPS2A matrix readback

Feb 25, 2009 at 10:12pm

VPS2A matrix readback

So, I’m finding Andrew Benson’s Video Processing patches to be extremely useful/helpful. I’m a little confused, however, on how to do matrix readback in this context. I suspect it has something to do with the “cc.uyvy2rgba.jxs @dimscale 2 1″ voodoo, and essentially doing the inverse of that? You can see in the attached patch where I’m trying to do the readback, and how it obviously isn’t working. Suggestions / help are much appreciated! Thanks, Michael

– Pasted Max Patch, click to expand. –
Feb 26, 2009 at 4:50am


What kind of problems are you experiencing? This seems to work as expected here. Maybe I am missing the intention of your patch?


Feb 26, 2009 at 5:58am

Hi Ben,
Thanks very much for your reply. This video shows http://psychoangelo.com/d/problempatch.mov

my problem. (There’s weird flipping stuff and flickering going on.) The video is made with the patch I included above.


Feb 26, 2009 at 8:30am


I had the same problem until I discover the following:
put a [jit.matrix] instead of [jit.matrix 4 char 160 120].

It works for me.

Feb 26, 2009 at 5:14pm

Thank you! This is really immediately useful for me. I don’t understand why this solution works (and the other doesn’t), but hey…


Feb 26, 2009 at 6:59pm


There was a bit of an issue with all of this with jit.gl.slab several versions ago, but it has been fixed for some time. Sounds like you are using an old version of Max 5. I highly recommend updating to Max 5.0.6.


Feb 26, 2009 at 7:04pm

What version of Max are you using? This sounds like a bug we fixed last year sometime. If you have updated to the latest version and are still getting the texture readback problems, let us know. In the meantime, a workaround I know of is to run the texture through a jit.gl.texture object before the matrix.
FWIW, I will also be including a record-to-disk section in the next installment of VPS tutorials.

Andrew B.

Feb 26, 2009 at 11:25pm

Thanks, and my bad on the updates. I’m always nervous to update right before I’ve got a something coming up, and that state seems to keep occurring. Will do it, though. Thanks again, Michael


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