How do I create a custom NSCursor with alpha mask?

Question

When I create a custom NSCursor in Objective-C the alpha channel mask appears to XOR the screen below. I am expecting an alpha channel value of zero to be transparent, not XOR the graphics below. I am certain my mask data is correct ARGB where A=0 for transparent and A=255 for opaque. What am I doing wrong?

static void maincustomcursor(bigmap *thedata, point hotspot)
{
    NSPoint thepoint;
    NSImage *newimage;
    NSCursor *thecursor;
    CGImageRef theimage;
    CGBitmapInfo theinfo;
    CGContextRef thecont;
    CGColorSpaceRef thecolor;
    int width, height, across;

    width = (*thedata).width;
    height = (*thedata).height;
    if (width != smalliconsize || height != smalliconsize) return;
    if (hotspot.h < 0) hotspot.h = 0;
    if (hotspot.h >= smalliconsize) hotspot.h = smalliconsize - 1;
    if (hotspot.v < 0) hotspot.v = 0;
    if (hotspot.v >= smalliconsize) hotspot.v = smalliconsize - 1;
    thepoint = NSMakePoint(hotspot.h, hotspot.v);
    across = (*thedata).rowbytes;
    thecolor = CGColorSpaceCreateDeviceRGB();
    theinfo = (CGBitmapInfo)kCGImageAlphaPremultipliedFirst;
    thecont = CGBitmapContextCreate((*thedata).baseaddr, width, height, 8, across, thecolor, theinfo);
    theimage = CGBitmapContextCreateImage(thecont);
    newimage = [[NSImage alloc] initWithCGImage:theimage size:NSZeroSize];
    thecursor = [[NSCursor alloc] initWithImage:newimage hotSpot:thepoint];
    [thecursor set];
    [thecursor release];
    [newimage release];
    CGImageRelease(theimage);
    CGContextRelease(thecont);
    CGColorSpaceRelease(thecolor);
}

Answer 1

OK I figured this out. When the alpha channel = 0 you need to be sure that red, green, and blue are also zero. If the alpha channel is zero and red, green, and blue are 255, then I am seeing XOR for the pixel. This may be related to the ancient way that cursors were implemented, with clear, white, black, and xor depending on the bit masks.