Invalid parameters in CGBitmapContext constructor

Question

I'm trying to create a blank bitmap in a Xamarin.iOS project using the CGBitmapContext constructor(s). However, no matter what I try I just get the error "System.Exception: Invalid parameters to context creation"

Example code:

const int width = 100; const int height = 100; const int bytesPerPixel = 4; const int bitsPerComponent = 8; var intBytes = width * height * bytesPerPixel; byte[] pixelData = new byte[intBytes]; var colourSpace = CGColorSpace.CreateDeviceRGB(); using (var objContext = new CGBitmapContext(pixelData, width, height, bitsPerComponent, width * bytesPerPixel, colourSpace, CGBitmapFlags.ByteOrderDefault)) { // ... }

I have tried changing most of the parameters; I tried fixing the data block and passing it as an IntPtr. I tried using null as the first parameter so that the system would allocate the data. And I've tried various flags in the last parameter. I always get that same error. What parameter is wrong? And what needs to be changed in the code above to make it execute?

Community · Accepted Answer · 2020-06-20 09:12:55Z

I changed last parameter from CGBitmapFlags.ByteOrderDefault to CGBitmapFlags.PremultipliedLast , and the error disappear.

refer to CGBitmapFlags Enumeration

As the link said

This enumeration specifies the layout information for the component data in a bitmap.

This enumeration determines the in-memory organization of the data and includes the color model, whether there is an alpha channel present and whether the component values have been premultiplied.

I think we have to select the corresponding flag to match the data info, especially the color model.

For the same reason, If you choose CreateDeviceCmyk , CGBitmapFlags.None will be appropriate.

Thanks, that indeed worked. I hadn't realised that the ColorSpace determined the arrangement of the bytes

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