> On Jan 10, 2018, at 4:42 PM, Nate Cook <natec...@apple.com> wrote:
>> Right. I guess my thought is that I would like them to be able to use a
>> standard creation pattern so it doesn’t vary from type to type (that is the
>> whole point of “unification” in my mind). In my own code, I have a concept
>> of constraint, of which a set are passed to the object being created. This
>> allows me to random create colors which look good together, etc…. I then
>> have some convenience methods which just automatically create an appropriate
>> constraint from a range where appropriate. I’d really like to see something
>> standard which allows for constraints other than simple ranges.
>
> Is it possible for you to share some of this code?
Sure. Small disclaimer that this was originally written back in the Swift 1~2
days, so it is overdue for a simplifying rewrite.
Also, I should point out that the term “Source” has a special meaning in my
code. It basically means that something will provide an ~infinite collection
of values of a type T. I have what I call a “ConstantSource” which just wraps
a T and gives it back when asked. But then I have a bunch of other “sources"
which let you create repeating patterns and do deferred calculations and things
like that. Finally I have a “RandomSource” which is part of what started this
discussion. You set up a RandomSource with a set of constraints, and then it
gives you random values of T that adhere to those constraints (e.g. colors with
a range of hues but the same saturation) whenever you ask for them.
This is really useful for doing things like graphic effects because, for
example, I can ask for a source of colors and a source of line widths and then
get out a large variety of interesting patterns from the same algorithm. I can
make simple stripes with ConstantSources, or I can make repeating patterns of
lines with repeating sources, or I can have random colors which look good
together by using a RandomSource. I can take a BezierPath and make it look
hand-drawn by breaking it into a bunch of lines and then offset the points a
small amount using a RandomSource of CGVectors.
Not sure how useful this concept of randomness (and pattern) is to others, but
I find it immensely useful! Not sure of the best way to implement it. The way
I do it is a type erased protocol with private conforming structs and then
public initializers on the type-erasing box. The end result is that I can just
say:
let myConst = Source(1) //ConstantSource with 1 as a value
let myPattern = Source([1, 2]) //OrderedSource which repeats 1, then 2
over and over forever
let myMeta = Source([myConst, myPattern]) //Will alternate between
sub-sources in order. Can be nested.
//…and so on.
It is quite extensible and can make very complex/interesting patterns very
easily. What I like about it is that (well controlled) random values and
patterns or constant values can be interchanged very easily.
The RandomSource has a RandomSourceCreatable Protocol that lets it take random
bits and turn them into objects/structs of T adhering to the given constraints.
This is way more complex under the hood than it needs to be, but it works well
in practice, and I haven’t gotten around to cleaning it up yet:
public protocol RandomSourceCreatable {
associatedtype ConstraintType = Self
///This should be implimented by simple types without internal
components
static func createRandom(rnd value:RandomSourceValue,
constraint:RandomSourceConstraint<ConstraintType>)->Self
///This should be implimented by complex types with multiple axis of
constraints
static func createRandom(rnd value:RandomSourceValue,
constraints:[String:RandomSourceConstraint<ConstraintType>])->Self
///Returns the proper dimension for the type given the constraints
static func dimension(given
contraints:[String:RandomSourceConstraint<ConstraintType>])->RandomSourceDimension
///Validates the given contraints to make sure they can create valid
objects. Only needs to be overridden for extremely complex types
static func validateConstraints(_
constraints:[String:RandomSourceConstraint<ConstraintType>])->Bool
///Convienience method which provides whitelist of keys for implicit
validation of constraints
static var allowedConstraintKeys:Set<String> {get}
}
Most of these things also have default implementations so you only really have
to deal with them for complex cases like colors or points. The constraints are
given using a dictionary with string keys and a RandomSourceConstraint value,
which is defined like this:
public enum RandomSourceConstraint<T> {
case none
case constant(T)
case min(T)
case max(T)
case range (T,T)
case custom ( (RandomSourceValue)->T )
//A bunch of boring convenience code here that transforms values so I
don’t always have to switch on the enum in other code that deals with this. I
just ask for the bounds or constrained T (Note: T here refers to the type for a
single axis as opposed to the generated type. e.g. CGFloat for a point)
}
I have found that this handles pretty much all of the constraints I need, and
the custom constraint is useful for anything exotic (e.g. sig-figs). The
RandomSource itself has convenience inits when T is Comparable that let you
specify a range instead of having to create the constraints yourself.
I then have conformed many standard types to RandomSourceCreatable so that I
can create Sources out of them. Here is CGPoint for reference:
extension CGPoint:RandomSourceCreatable {
public static func dimension(given
contraints:[String:RandomSourceConstraint<CGFloat>])->RandomSourceDimension {
return RandomSourceDimension.manyWord(2)
}
public typealias ConstraintType = CGFloat
public static var allowedConstraintKeys:Set<String>{
return ["x","y"]
}
public static func createRandom(rnd value:RandomSourceValue,
constraints:[String:RandomSourceConstraint<CGFloat>])->CGPoint {
let xVal = value.value(at: 0)
let yVal = value.value(at: 1)
//Note: Ints have a better distribution for normal use cases of
points
let x = CGFloat(Int.createRandom(rnd: xVal, constraint:
constraints["x"]?.asType({Int($0 * 1000)}) ?? .none))/1000
let y = CGFloat(Int.createRandom(rnd: yVal, constraint:
constraints["y"]?.asType({Int($0 * 1000)}) ?? .none))/1000
return CGPoint(x: x, y: y)
}
}
Notice that I have a RandomSourceValue type that provides the random bits of
the requested dimension. When I get around to updating this, I might do
something closer to the proposal, where I would just pass the generator and
grab bits as needed. The main reason I did it the way I did is that it lets me
have random access to the source very easily.
The ‘asType’ method converts a constraint to work with another type (in this
case Ints).
Colors are a bit more complicated, mainly because I allow a bunch of different
constraints, and I also have validation code to make sure the constraints fit
together properly. I also ask for different amounts of randomness based on
whether it is greyscale or contains alpha. Just to give you a sense, here are
the allowed constraint keys for a CGColor:
public static var allowedConstraintKeys:Set<String>{
return ["alpha","gray","red","green","blue", "hue", "saturation",
"brightness"]
}
and here is the creation method when the keys are for RGBA (I have similar
sections for HSBA and greyscale):
let rVal = value.value(at: 0)
let gVal = value.value(at: 1)
let bVal = value.value(at: 2)
let aVal = value.value(at: 3)
let r = CGFloat.createRandom(rnd: rVal, constraint: constraints["red"] ??
.range(0,1))
let g = CGFloat.createRandom(rnd: gVal, constraint: constraints["green"] ??
.range(0,1))
let b = CGFloat.createRandom(rnd: bVal, constraint: constraints["blue"] ??
.range(0,1))
let a = CGFloat.createRandom(rnd: aVal, constraint: constraints["alpha"] ??
.constant(1.0))
return self.init(colorSpace: CGColorSpaceCreateDeviceRGB(), components:
[r,g,b,a])!
The end result is that initializing a source of CGColors looks like this
(either parameter can be omitted if desired):
let colorSource:Source<CGColor> = Source(seed: optionalSeed,
constraints:["saturation": .constant(0.4), "brightness": .constant(0.6)])
Anyway, I hope this was useful/informative. I know the code is a bit messy,
but I still find it enormously useful in practice. I plan to clean it up when
I find time, simplifying the RandomSourceValue stuff and moving from String
Keys to a Struct with static functions for the constraints. The new
constraints will probably end up looking like this:
let colorSource:Source<CGColor> = Source(seed: optionalSeed,
constraints:[.saturation(0.4), .brightness(0.4...0.6)])
Thanks,
Jon
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