Detect QRCode in a thread

[AndreMiras]

See requirement description: kivy-garden/garden.zbarcam@d6a41a6#commitcomment-25806577

[AndreMiras]

@glins97, in the feature/ticket7_detect_qrcode_in_a_thread branch, I'm now making the detection in thread. It seems to work OK on my phone, but I haven't tried on low-end device yet.
Could you give it a try on your device and come back to me?

[glins97]

Nice!
It is indeed threaded, but now the camera stutters. The problem was with pixels and image_data. You rocked.
Modified your solution a little, but still good results. Is the camera smooth on your phone? Just ran on a S7 and was really stuttery.
Anyways, nice solution @AndreMiras!

[glins97]

I'm puzzled by the threaded stuttering. Should I upload a video?

[AndreMiras]

Interesting, I've tested it on a Honor 5C and I simulated a lag my adding a time.sleep() in _detect_qrcode_frame(). It totally improved it with the thread. However I've tested it on an older device like Nexus 4 and I could see it didn't change that much.
I still have few ideas for improving it.

1. enable only the type you need, e.g. QR codes (i.e. disable bar code and other types)
2. do not process every frame, but for example 1/3 of them (i.e. using a modulo 3)
3. do not process the entire frame, but only part of it (like what we see in other scanners with other part of the screen greyed out)

I think you can easily give a try to 1 and 2 and tell me how it went.

[glins97]

Holy crap, I just read my previous comment and am sorry for the way I worded it.
Anyways:

1. Really good improvement! Still feels laggy, but it's much better. Adding this two lines on init solves it:
   self.scanner.set_config(0, zbar.Config.ENABLE, 0) # disables every scanning self.scanner.set_config(zbar.Symbol.QRCODE, zbar.Config.ENABLE, 1) # enables qr scanning
2. Tried that (with modulos 2, 3, 5 and 10) aswell with specific timings (200ms, 500ms, 1000ms) but in the end we're setting a delay for the scan, which is the cause of stuttering. So that improves the medium fps, but makes it more stuttery.
3. Giving a shot at it right now. I'll tell you how it goes. BTW, my xcamera is not full screened. You know how to increase its size? It's resolution property is only changes ppi and not size, and it's size doesn't change anything that I could notice.

[AndreMiras]

1. OK good news, if you want to do it in a DRY/object fashion inherit ZBarCam class and overrides __init__() method
2. The idea is not to add a timing, but only process one frame every "x" frames. So basically just something like if self.count % 5 != 0: return
3. Good luck on that one. Yes it's not full screen for me either I think there're quite some things to fix upstream in Kivy to make it work properly. I've played with that yesterday, but there's quite some work to do. I should probably create a dedicated ticket for that one
4. bonus point, decreasing the cam resolution could also help to make it faster to process

[AndreMiras]

For the resolution/size I've posted some of my finding in a dedicated ticket kivy-garden/garden.zbarcam#8

[glins97]

I'll check yout ticket and tell you how it goes.
About 2: tried with a specific number of frames and with timings, but results were the same. Stuttery. I'm not sure how threading didn't fix that. Maybe creating the Thread object is causing load?
Anyways, I'll keep working on that.

[AndreMiras]

@glins97 I've just published full screen fix/workaround (develop branch), could you give it a try on your device?

[Cheaterman]

Didn't know this was a thing so I did that: #39