wangs_formula.cc

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// 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.
 
#include "impeller/geometry/wangs_formula.h"
 
namespace impeller {
 
namespace {
 
// Don't allow linearized segments to be off by more than 1/4th of a pixel from
// the true curve. This value should be scaled by the max basis of the
// X and Y directions.
constexpr static Scalar kPrecision = 4;
 
constexpr Scalar length(Point n) {
  Point nn = n * n;
  return std::sqrt(nn.x + nn.y);
}
 
}  // namespace
 
Scalar ComputeCubicSubdivisions(Scalar scale_factor,
                                Point p0,
                                Point p1,
                                Point p2,
                                Point p3) {
  Scalar k = scale_factor * .75f * kPrecision;
  Point a = (p0 - p1 * 2 + p2).Abs();
  Point b = (p1 - p2 * 2 + p3).Abs();
  return std::sqrt(k * length(a.Max(b)));
}
 
Scalar ComputeQuadradicSubdivisions(Scalar scale_factor,
                                    Point p0,
                                    Point p1,
                                    Point p2) {
  Scalar k = scale_factor * .25f * kPrecision;
  return std::sqrt(k * length(p0 - p1 * 2 + p2));
}
 
Scalar ComputeQuadradicSubdivisions(Scalar scale_factor,
                                    const QuadraticPathComponent& quad) {
  return ComputeQuadradicSubdivisions(scale_factor, quad.p1, quad.cp, quad.p2);
}
 
Scalar ComputeCubicSubdivisions(float scale_factor,
                                const CubicPathComponent& cub) {
  return ComputeCubicSubdivisions(scale_factor, cub.p1, cub.cp1, cub.cp2,
                                  cub.p2);
}
 
}  // namespace impeller