How do I create an alpha only bitmap context

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失恋的感觉
失恋的感觉 2021-01-11 17:48

Apple tech note QA1037 says \"To create an alpha-only bitmap context simply pass NULL for the colorspace parameter.\"

However, I am not sure what to pass for the

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  •  花落未央
    2021-01-11 18:17

    The docs clearly state you can use values from the CGImageAlphaInfo even though the parameter is defined as needed a value from the CGBitmapInfo enum.

    One solution would be to cast the value:

    (CGBitmapInfo)kCGImageAlphaOnly
    

    That will make the compiler happy.

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