| Flutter Impeller |

sigma.h
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1 // Copyright 2013 The Flutter Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #pragma once
6
7 #include "impeller/geometry/scalar.h"
8
9 namespace impeller {
10
11 /// For filters that use a Gaussian distribution, this is the `Radius` size to
12 /// use per `Sigma` (standard deviation).
13 ///
14 /// This cutoff (sqrt(3)) is taken from Flutter and Skia (where the
15 /// multiplicative inverse of this constant is used (1 / sqrt(3)):
16 /// https://api.flutter.dev/flutter/dart-ui/Shadow/convertRadiusToSigma.html
17 ///
18 /// In practice, this value is somewhat arbitrary, and can be changed to a
19 /// higher number to integrate more of the Gaussian function and render higher
20 /// quality blurs (with exponentially diminishing returns for the same sigma
21 /// input). Making this value any lower results in a noticable loss of
22 /// quality in the blur.
23 constexpr static float kKernelRadiusPerSigma = 1.73205080757;
24
25 struct Radius;
26
27 /// @brief In filters that use Gaussian distributions, "sigma" is a size of
28 /// one standard deviation in terms of the local space pixel grid of
29 /// the filter input. In other words, this determines how wide the
30 /// distribution stretches.
31 struct Sigma {
32 Scalar sigma = 0.0;
33
34 constexpr Sigma() = default;
35
36 explicit constexpr Sigma(Scalar p_sigma) : sigma(p_sigma) {}
37
38 operator Radius() const; // NOLINT(google-explicit-constructor)
39 };
40
41 /// @brief For convolution filters, the "radius" is the size of the
42 /// convolution kernel to use on the local space pixel grid of the
43 /// filter input.
44 /// For Gaussian blur kernels, this unit has a linear
45 /// relationship with `Sigma`. See `kKernelRadiusPerSigma` for
46 /// details on how this relationship works.
47 struct Radius {
48 Scalar radius = 0.0;
49
50 constexpr Radius() = default;
51
52 explicit constexpr Radius(Scalar p_radius) : radius(p_radius) {}
53
54 operator Sigma() const; // NOLINT(google-explicit-constructor)
55 };
56
57 } // namespace impeller
impeller::Sigma::sigma
Scalar sigma
Definition: sigma.h:32
impeller::Radius::radius
Scalar radius
Definition: sigma.h:48
impeller::Scalar
float Scalar
Definition: scalar.h:15
impeller::Radius::Radius
constexpr Radius(Scalar p_radius)
Definition: sigma.h:52
impeller::Radius::Radius
constexpr Radius()=default
impeller::Radius
For convolution filters, the "radius" is the size of the convolution kernel to use on the local space...
Definition: sigma.h:47
impeller::Sigma::Sigma
constexpr Sigma()=default
impeller::Sigma
In filters that use Gaussian distributions, "sigma" is a size of one standard deviation in terms of t...
Definition: sigma.h:31
scalar.h
impeller::kKernelRadiusPerSigma
constexpr static float kKernelRadiusPerSigma
Definition: sigma.h:23
impeller::Sigma::Sigma
constexpr Sigma(Scalar p_sigma)
Definition: sigma.h:36
impeller
Definition: aiks_context.cc:10