CGBitmapImageContext and CGBitmapInfo + CGImageAlphaInfo

[Vitaly]

I want to create CGBitmapContext from Java, I see "create" static method mapped to CGBitmapContextCreate(), but there is a problem passing parameters. From Apple docs:

> bitmapInfo

> Constants that specify whether the bitmap should contain an alpha channel, the alpha channel’s relative location in a pixel, and information about whether the pixel components are floating-point or integer values. The constants for specifying the alpha channel information are declared with the CGImageAlphaInfo type but can be passed to this parameter safely.

I see CGBitmapInfo and CGImageAlphaInfo enums in cocoatouch bindings, but "create" method allows only CGBitmapInfo, where it should accept mask of CGBitmapInfo and CGImageAlphaInfo constants. Is it possible to fix?

[Max Morawski]

I agree it would be nice to have a tidy API for this but in the mean time you can define the constants yourself:

    public static final int kCGImageAlphaNone = 0; /* For example, RGB. */
    public static final int kCGImageAlphaPremultipliedLast = 1; /* For example, premultiplied RGBA */
    public static final int kCGImageAlphaPremultipliedFirst = 2; /* For example, premultiplied ARGB */
    public static final int kCGImageAlphaLast = 3; /* For example, non-premultiplied RGBA */
    public static final int kCGImageAlphaFirst = 4; /* For example, non-premultiplied ARGB */
    public static final int kCGImageAlphaNoneSkipLast = 5; /* For example, RBGX. */
    public static final int kCGImageAlphaNoneSkipFirst = 6; /* For example, XRGB. */
    public static final int kCGImageAlphaOnly = 7; /* No color data, alpha data only */

    public static final int kCGBitmapAlphaInfoMask = 0x1F;
    public static final int kCGBitmapFloatComponents = (1 << 8);
    public static final int kCGBitmapByteOrderMask = 0x7000;
    public static final int kCGBitmapByteOrderDefault = (0 << 12);
    public static final int kCGBitmapByteOrder16Little = (1 << 12);
    public static final int kCGBitmapByteOrder32Little = (2 << 12);
    public static final int kCGBitmapByteOrder16Big = (3 << 12);
    public static final int kCGBitmapByteOrder32Big = (4 << 12);

    // from https://developer.apple.com/library/mac/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html
    // Table 2-1  Pixel formats supported for bitmap graphics contexts (iOS only)
    // CS    Pixel format and bitmap information constant
    // Null  8 bpp, 8 bpc, kCGImageAlphaOnly
    // Gray  8 bpp, 8 bpc,kCGImageAlphaNone
    // Gray  8 bpp, 8 bpc,kCGImageAlphaOnly
    // RGB   16 bpp, 5 bpc, kCGImageAlphaNoneSkipFirst
    // RGB   32 bpp, 8 bpc, kCGImageAlphaNoneSkipFirst
    // RGB   32 bpp, 8 bpc, kCGImageAlphaNoneSkipLast
    // RGB   32 bpp, 8 bpc, kCGImageAlphaPremultipliedFirst
    // RGB   32 bpp, 8 bpc, kCGImageAlphaPremultipliedLast

    public static CGBitmapInfo bitmapInfo(boolean withAlpha) {
        return new CGBitmapInfo(withAlpha ? kCGImageAlphaPremultipliedLast : kCGImageAlphaNoneSkipLast);
    }

Please note I put a complete set of constants there for reference; some will not work on iOS and/or in all circumstances.

HTH,
Max