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/*
* Copyright 2023 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkCubics_DEFINED
#define SkCubics_DEFINED
/**
* Utilities for dealing with cubic formulas with one variable:
* f(t) = A*t^3 + B*t^2 + C*t + d
*/
class SkCubics {
public:
/**
* Puts up to 3 real solutions to the equation
* A*t^3 + B*t^2 + C*t + d = 0
* in the provided array and returns how many roots that was.
*/
static int RootsReal(double A, double B, double C, double D,
double solution[3]);
/**
* Puts up to 3 real solutions to the equation
* A*t^3 + B*t^2 + C*t + D = 0
* in the provided array, with the constraint that t is in the range [0.0, 1.0],
* and returns how many roots that was.
*/
static int RootsValidT(double A, double B, double C, double D,
double solution[3]);
/**
* Puts up to 3 real solutions to the equation
* A*t^3 + B*t^2 + C*t + D = 0
* in the provided array, with the constraint that t is in the range [0.0, 1.0],
* and returns how many roots that was.
* This is a slower method than RootsValidT, but more accurate in circumstances
* where floating point error gets too big.
*/
static int BinarySearchRootsValidT(double A, double B, double C, double D,
double solution[3]);
/**
* Evaluates the cubic function with the 4 provided coefficients and the
* provided variable.
*/
static double EvalAt(double A, double B, double C, double D, double t) {
return A * t * t * t +
B * t * t +
C * t +
D;
}
static double EvalAt(double coefficients[4], double t) {
return EvalAt(coefficients[0], coefficients[1], coefficients[2], coefficients[3], t);
}
};
#endif
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