On Nov 28, 2009, at 2:50 PM, Quincey Morris wrote:
> On Nov 27, 2009, at 14:58, Shane wrote:
>
>> I think I'm understanding this in part ...
>>
>> // *.h
>> NSMutableData *pointData;
>> NSPointArray *points;
>>
>> // *.m
>> pointData = [[NSMutableData alloc] init];
>>
>> ...
>>
>> NSPoint point = NSMakePoint([iters floatValue], [mse floatValue]);
>> // not sure how to get an NSPoint into NSMutableData?
>>
>> // here I resize NSMutableData, but this will always only be
>> // increasing the length by 1.
>> [pointData increaseLenghtBy:sizeof(NSPoint)];
>>
>> // and here I assign the data to NSPointArray
>> points = (NSPoint *) [pointData bytes];
>>
>> And from here I can pass this NSPointArray around till I get to the
>> point where I will use this data for my NSBezierPath. Will
>> NSBezierPath (which takes an NSPointArray) be able to properly read
>> from 'points' by doing the above?
>
> In part, but not quite. Although Graham's advice was good, and might be a
> better approach, for completeness here's how this approach works.
>
> You only need one instance variable:
>
> NSMutableData *pointData;
>
> which you can initialize as above.
>
> To add a point, I'd do something like this:
>
> NSUInteger pointCount = [pointData length] / sizeof (NSPoint);
> [pointData setLength: (pointCount + 1) * sizeof (NSPoint)];
> NSPointArray points = [pointData mutableBytes];
> points [pointCount] = somePoint;
>
> To add the points to a Bezier path:
>
> [somePath appendBezierPathWithPoints: [pointData mutableBytes] count:
> [pointData length] / sizeof (NSPoint)];
>
> Note:
>
> 1. 'NSPointArray*' isn't the correct type for an array of points. Plain
> 'NSPointArray' is what you want.
>
> 2. You will get a compiler warning if you try to assign [pointData bytes] to
> the NSPointArray variable, because the [point bytes] is of type 'const
> void*'. You need [pointData mutableBytes] which is just of type 'void*'.
>
> 3. There's no need to cast [point mutableBytes] to NSPointArray because
> there's no warning assigning from 'void*' to a compatible pointer type.
> Casting it is not wrong, but any time you write an explicit cast, you're
> overriding much of the compiler's type checking, so it's easy to introduce
> bugs that way. (Not likely in this case, but as a general consideration.)
> It's a personal thing, though -- I guess some people like to have the
> explicit cast because it documents what the code is supposed to be doing.
Another possible approach is simply use a NSMutableArray full of NSValue
objects that contain
the NSPoint structures . . .
Cheers,
. . . . . . . . Henry
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