1 #include <mbgl/util/tiny_sdf.hpp>
2
3 #include <mbgl/util/math.hpp>
4
5 #include <algorithm>
6
7 namespace mbgl {
8 namespace util {
9
10 namespace tinysdf {
11
12 static const double INF = 1e20;
13
14 // 1D squared distance transform
edt1d(std::vector<double> & f,std::vector<double> & d,std::vector<int16_t> & v,std::vector<double> & z,uint32_t n)15 void edt1d(std::vector<double>& f,
16 std::vector<double>& d,
17 std::vector<int16_t>& v,
18 std::vector<double>& z,
19 uint32_t n) {
20 v[0] = 0;
21 z[0] = -INF;
22 z[1] = +INF;
23
24 for (uint32_t q = 1, k = 0; q < n; q++) {
25 double s = ((f[q] + q * q) - (f[v[k]] + v[k] * v[k])) / (2 * q - 2 * v[k]);
26 while (s <= z[k]) {
27 k--;
28 s = ((f[q] + q * q) - (f[v[k]] + v[k] * v[k])) / (2 * q - 2 * v[k]);
29 }
30 k++;
31 v[k] = q;
32 z[k] = s;
33 z[k + 1] = +INF;
34 }
35
36 for (uint32_t q = 0, k = 0; q < n; q++) {
37 while (z[k + 1] < q) k++;
38 d[q] = (q - v[k]) * (q - v[k]) + f[v[k]];
39 }
40 }
41
42
43 // 2D Euclidean distance transform by Felzenszwalb & Huttenlocher https://cs.brown.edu/~pff/dt/
edt(std::vector<double> & data,uint32_t width,uint32_t height,std::vector<double> & f,std::vector<double> & d,std::vector<int16_t> & v,std::vector<double> & z)44 void edt(std::vector<double>& data,
45 uint32_t width,
46 uint32_t height,
47 std::vector<double>& f,
48 std::vector<double>& d,
49 std::vector<int16_t>& v,
50 std::vector<double>& z) {
51 for (uint32_t x = 0; x < width; x++) {
52 for (uint32_t y = 0; y < height; y++) {
53 f[y] = data[y * width + x];
54 }
55 edt1d(f, d, v, z, height);
56 for (uint32_t y = 0; y < height; y++) {
57 data[y * width + x] = d[y];
58 }
59 }
60 for (uint32_t y = 0; y < height; y++) {
61 for (uint32_t x = 0; x < width; x++) {
62 f[x] = data[y * width + x];
63 }
64 edt1d(f, d, v, z, width);
65 for (uint32_t x = 0; x < width; x++) {
66 data[y * width + x] = std::sqrt(d[x]);
67 }
68 }
69 }
70
71 } // namespace tinysdf
72
transformRasterToSDF(const AlphaImage & rasterInput,double radius,double cutoff)73 AlphaImage transformRasterToSDF(const AlphaImage& rasterInput, double radius, double cutoff) {
74 uint32_t size = rasterInput.size.width * rasterInput.size.height;
75 uint32_t maxDimension = std::max(rasterInput.size.width, rasterInput.size.height);
76
77 AlphaImage sdf(rasterInput.size);
78
79 // temporary arrays for the distance transform
80 std::vector<double> gridOuter(size);
81 std::vector<double> gridInner(size);
82 std::vector<double> f(maxDimension);
83 std::vector<double> d(maxDimension);
84 std::vector<double> z(maxDimension + 1);
85 std::vector<int16_t> v(maxDimension);
86
87 for (uint32_t i = 0; i < size; i++) {
88 double a = double(rasterInput.data[i]) / 255; // alpha value
89 gridOuter[i] = a == 1.0 ? 0.0 : a == 0.0 ? tinysdf::INF : std::pow(std::max(0.0, 0.5 - a), 2.0);
90 gridInner[i] = a == 1.0 ? tinysdf::INF : a == 0.0 ? 0.0 : std::pow(std::max(0.0, a - 0.5), 2.0);
91 }
92
93 tinysdf::edt(gridOuter, rasterInput.size.width, rasterInput.size.height, f, d, v, z);
94 tinysdf::edt(gridInner, rasterInput.size.width, rasterInput.size.height, f, d, v, z);
95
96 for (uint32_t i = 0; i < size; i++) {
97 double distance = gridOuter[i] - gridInner[i];
98 sdf.data[i] = std::max(0l, std::min(255l, ::lround(255.0 - 255.0 * (distance / radius + cutoff))));
99 }
100
101 return sdf;
102 }
103
104 } // namespace util
105 } // namespace mbgl
106