How to access VisionKit?

[emkay_online]

Hi,

I'm just dipping my toes into objc_util and have fallen at the first hurdle.

I want to write a small script that calls VisionKit to scan a document and return the result to Pythonista. API is here: https://developer.apple.com/documentation/visionkit

I've started with:

from objc_util import *
VNDocumentCameraViewController = ObjCClass('VNDocumentCameraViewController')

But Pythonista says that the class VNDocumentCameraViewController doesn't exist.

I'd love some help getting past this (and if anyone could take the example further, that would be amazing).

Thank you,

Martin

[JonB]

i think the document object guves you UIImages only, but you could create a pdf using some UIKit functions:

https://developer.apple.com/documentation/uikit/images_and_pdf?language=objc

(you need to acces the functions using c.UIGraphicsBeginPDFContextToFile etc and set argtypes and restype)

I think the basic flow is, you have to create a pdf context to a file, begn a pdf page, draw your content (UiImage's drawAtPoint ), begn a new page, etc, then finally end the context.

[cvp]

Do you know that PIL save has an option to save as pdf?

pil_image.save('File.pdf',"PDF",resolution=100.0) 

[stephen]

@cvp this would of been wonderfull information about 3 months go lol

[JonB]

@cvp can PIL do multipage PDF? I guess you still would need to do the ui2pil type business.

[mikael]

@JonB said:

@cvp can PIL do multipage PDF? I guess you still would need to do the ui2pil type business.

Which I guess would make it slow in a way that this type of use case does not reslly tolerate.

Playing with the idea of a truly personalized doc scanner that would put the scan whete it needs to go. Also, combining this with the text recognition stuff would be good (as soon as they get international characters right).

[JonB]

But the built in objc methods for writing to PDF (see link above) ought to be reasonably fast. I haven't tried.

[cvp]

@JonB said:

can PIL do multipage PDF? I guess you still would need to do the ui2pil type business.

I don't think it does multi pages, but easy to do it yourself via PdfFileMerger.
Yes for ui2pil

[cvp]

@JonB said:

But the built in objc methods for writing to PDF (see link above) ought to be reasonably fast. I haven't tried

I have already done the inverse (PDF -> image) via Objectivec context.. quick 🙄

[emkay_online]

@cvp Thank you so much for this code. It works a treat and really gives me a solid foundation to build on.

Also thank you for giving me a good grounding in the objc_util module - it's certainly a complex one, especially for someone with no iOS coding experience.

Thank you.

[cvp]

@emkay_online you should dismiss the viewcontroller in the didcancel delegate, not in the didfinish like I did for testing only. This if you want to process multiple scans

[cvp]

@JonB said:

But the built in objc methods for writing to PDF (see link above) ought to be reasonably fast. I haven't tried.

Please applaus. ok, I exaggerate 😂, but was not so easy (for me)

from objc_util import *
import ui

UIGraphicsGetCurrentContext = c.UIGraphicsGetCurrentContext
UIGraphicsGetCurrentContext.restype = c_void_p
UIGraphicsGetCurrentContext.argtypes = []

UIGraphicsBeginPDFContextToData = c.UIGraphicsBeginPDFContextToData
UIGraphicsBeginPDFContextToData.restype = None
UIGraphicsBeginPDFContextToData.argtypes = [c_void_p, CGRect, c_void_p]

UIGraphicsBeginPDFPage = c.UIGraphicsBeginPDFPage
UIGraphicsBeginPDFPage.restype = None
UIGraphicsBeginPDFPage.argtypes = []

UIGraphicsEndPDFContext = c.UIGraphicsEndPDFContext
UIGraphicsEndPDFContext.restype = None
UIGraphicsEndPDFContext.argtypes = []

pdfdata = NSMutableData.alloc()#.init()
ui_image = ui.Image.named('test:Lenna')
uiimage = ObjCInstance(ui_image)
w,h = ui_image.size
frame = CGRect(CGPoint(0, 0), CGSize(w, h)) 
UIGraphicsBeginPDFContextToData(pdfdata, frame, None)
UIGraphicsBeginPDFPage()
pdfContext = UIGraphicsGetCurrentContext()
uiimage.drawInRect_(frame)
UIGraphicsEndPDFContext()
# just to be sure that pdfdata is ok
with open('a.pdf',mode='wb') as fil:
    b = nsdata_to_bytes(pdfdata)
    fil.write(b) 

[JonB]

👏👏👏

If you are going straight to file, you might consider using

https://developer.apple.com/documentation/uikit/1623927-uigraphicsbeginpdfcontexttofile?language=objc

instead of creating the context as nsdata. Might save a few lines.

Also, you can use drawAtPoint instead of drawInRect, so that you don't need to specify w,h.

I think if you omit the frame when you create the context, it also create an 8.5x11.

[cvp]

@JonB said:

so that you don't need to specify w,h.

Yes but UIGraphicsBeginPDFContextToData needs it also

Édit: sorry, written before reading your last line

[cvp]

I don't say it is the best way, it was only an exercice for me.

[cvp]

@JonB said:

instead of creating the context as nsdata.

I added the file lines only to test /check pdfdata.