On Tue, 9 Nov 2021 10:43:40 GMT, Laurent Bourgès <[email protected]> wrote:
>> I don't think I can implement that on my own. Even if I fully understood the
>> julia code, I assume I'd want to use the Math.fma(..) method. That method
>> uses BigDecimals, which I assume (?) we don't want to use in a loop like
>> this for performance reasons.
>>
>> If this level of high-precision is considered essential to resolving this
>> bug: then personally I'm at an impasse and we should either close this PR or
>> I'll need some external help.
>>
>> Or possible compromises might include:
>>
>> A. Add a method like this in Curve.java:
>>
>> public double evaluateCubicPolynomial(double a, double b, double c, double
>> d, double t) {
>> return d + t * (c + t * (b + t * a)));
>> }
>>
>>
>> And add a ticket that someone else can address separately to improve the
>> accuracy of that method. (Also maybe other areas in the AWT codebase should
>> use the same method? Like `Order3#XforT`?)
>>
>> B. We can modify my new method signature from:
>> `public static Rectangle2D getBounds2D(PathIterator pi)`
>> to:
>> `public static Rectangle2D getBounds2D(PathIterator pi, boolean
>> highPrecision)`
>>
>> Where if `highPrecision` is true we use the new implementation *which may
>> suffer rounding errors and be a few ulps too small*. And if it is false then
>> we use the old implementation which suffers from the original bug. This has
>> the benefit of definitely not breaking any existing code in existence. The
>> downside is it puts the responsibility on developers to learn about and
>> implement this new method. But at least it would exist.
>>
>> Thoughts?
>
> I agree it is out of the scope of this issue to implement high-precision
> polynom evaluation (compensated horder scheme), that I or anybody else could
> implement it later.
> To ensure bounds2D are enclosing the shape entirely, I propose to add a small
> margin (10 ulps or more) to ascertain precision is good enough.
> To determine the precision level, using fuzzy testing is the good approach :
> generate lots ofrandom paths => check bounds2D accuracy in ulp units.
@prrace @mrserb what do you think on this bug in terms of precision
requirements?
- should bbox always include control points ?
- should ideal shape always fit in bbox ? So I propose to add a margin >
numerical inaccuracies.
I can develop a numerical approach based on fuzzy testing:
- generate random curves (high magnitude changes on control points)
- use both this algorithm (double) and implement the same with BigDecimal
- estimate the extrema error = max distance(pts big decimal, pts double)
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PR: https://git.openjdk.java.net/jdk/pull/6227
