// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

part of dart.ui;

/// Linearly interpolate between two numbers, `a` and `b`, by an extrapolation
/// factor `t`.
///
/// When `a` and `b` are equal or both NaN, `a` is returned.  Otherwise,
/// `a`, `b`, and `t` are required to be finite or null, and the result of `a +
/// (b - a) * t` is returned, where nulls are defaulted to 0.0.
double? lerpDouble(num? a, num? b, double t) {
  if (a == b || (a?.isNaN ?? false) && (b?.isNaN ?? false)) {
    return a?.toDouble();
  }
  a ??= 0.0;
  b ??= 0.0;
  assert(a.isFinite, 'Cannot interpolate between finite and non-finite values');
  assert(b.isFinite, 'Cannot interpolate between finite and non-finite values');
  assert(t.isFinite, 't must be finite when interpolating between values');
  return a * (1.0 - t) + b * t;
}

/// Linearly interpolate between two doubles.
///
/// Same as [lerpDouble] but specialized for non-null `double` type.
double _lerpDouble(double a, double b, double t) {
  // This doesn't match _lerpInt to preserve specific behaviors when dealing
  // with infinity and nan.
  return a * (1.0 - t) + b * t;
}

/// Linearly interpolate between two integers.
///
/// Same as [lerpDouble] but specialized for non-null `int` type.
double _lerpInt(int a, int b, double t) {
  return a + (b - a) * t;
}
