Playground CGContext nil

Question

Hi!

When run below code in iOS blank Playground

Code Block import UIKit
let contextBig = CGContext(
    data: nil,
    width: 560,
    height: 560,
    bitsPerComponent: 8,
    bytesPerRow: 2240,
    space: CGColorSpace(name: CGColorSpace.sRGB)!,
    bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)
print (contextBig as Any)

Result in console:

Code Block Optional(<CGContext 0x600003cc0540> (kCGContextTypeBitmap)
	<<CGColorSpace 0x600002ddc300> (kCGColorSpaceICCBased; kCGColorSpaceModelRGB; sRGB IEC61966-2.1)>
		width = 560, height = 560, bpc = 8, bpp = 32, row bytes = 2240 
		kCGImageAlphaPremultipliedFirst | 0 (default byte order) | kCGImagePixelFormatPacked (default) )

But when change width and height to 561, result in console:

Code Block nil

Is there for playground some memory limits or etc?

Xcode - Version 12.3 (12C33)

1.3k

Posted by

olegl

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Answer 1

Is there for playground some memory limits or etc?

Not clearly documented, but there might have been.

As far as I tried your code on Xcode Playground of 12.4, it showed non nil result.
The issue may be fixed in 12.4, or some other things may be affecting.

Posted by

OOPer

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Answer 2

Is there for playground some memory limits or etc?

Not clearly documented, but there might have been.

As far as I tried your code on Xcode Playground of 12.4, it showed non nil result.
The issue may be fixed in 12.4, or some other things may be affecting.

Posted by

OOPer

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Answer 3

OOPer , thank you for your results.

I upgraded Xcode to 12.4, but no luck.
With params 560 - not nil, with 561 - nil.

My system configuration is

MacBook Air (Retina, 13-inch, 2020), 16GB RAM, i5
macOS Catalina 10.15.7 (19H524)
Xcode Version 12.4 (12D4e)

Also I tried set env variables CGBITMAP_CONTEXT_LOG_ERRORS, CG_CONTEXT_SHOW_BACKTRACE, but I don't have additional info in console.

Posted by

olegl

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Answer 4

macOS Catalina 10.15.7 (19H524)

Thanks for clarifying. I tried on Mac mini 2018 with macOS Big Sur 11.1.
Quite interesting difference.Not sure any of the settings may be affecting or not.

Posted by

OOPer

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Answer 5

OOPer , thank you for your help!

I runed code in blank test iOS app and see in console

Code Block 2021-02-27 13:15:29.587193+0300 TestApp[2104:187450] [Unknown process name] CGBitmapContextCreate: invalid data bytes/row: should be at least 2244 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedFirst.
nil

So my mistake is use bytesPerRow: 2240 as constant, but increase width. In my original playground I use bytesPerRow from old image, but only increase image(context)size for new image.

Correct using CGContext with data = nil, you can pass bytesPerRow: 0 for auto calc.

It's sorry of course that Playground don't show all message in console like simulator.

Posted by

olegl

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Answer 6

Thanks for revealing the fact you found. In fact, I was just changing height while trying (although you clearly described change width and height in your original post). Will try to help better if I have next chance.

Posted by

OOPer

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Playground CGContext nil

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