103 lines
3.2 KiB
C++
103 lines
3.2 KiB
C++
#include <mbgl/util/tiny_sdf.hpp>
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#include <mbgl/util/math.hpp>
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#include <algorithm>
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namespace mbgl {
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namespace util {
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namespace tinysdf {
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static const double INF = 1e20;
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// 1D squared distance transform
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void edt1d(
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std::vector<double>& f, std::vector<double>& d, std::vector<int16_t>& v, std::vector<double>& z, uint32_t n) {
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v[0] = 0;
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z[0] = -INF;
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z[1] = +INF;
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for (uint32_t q = 1, k = 0; q < n; q++) {
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double s = ((f[q] + q * q) - (f[v[k]] + v[k] * v[k])) / (2 * q - 2 * v[k]);
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while (s <= z[k]) {
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k--;
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s = ((f[q] + q * q) - (f[v[k]] + v[k] * v[k])) / (2 * q - 2 * v[k]);
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}
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k++;
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v[k] = q;
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z[k] = s;
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z[k + 1] = +INF;
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}
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for (uint32_t q = 0, k = 0; q < n; q++) {
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while (z[k + 1] < q) k++;
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d[q] = (static_cast<double>(q) - v[k]) * (static_cast<double>(q) - v[k]) + f[v[k]];
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}
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}
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// 2D Euclidean distance transform by Felzenszwalb & Huttenlocher https://cs.brown.edu/~pff/dt/
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void edt(std::vector<double>& data,
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uint32_t width,
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uint32_t height,
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std::vector<double>& f,
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std::vector<double>& d,
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std::vector<int16_t>& v,
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std::vector<double>& z) {
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for (uint32_t x = 0; x < width; x++) {
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for (uint32_t y = 0; y < height; y++) {
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f[y] = data[y * width + x];
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}
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edt1d(f, d, v, z, height);
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for (uint32_t y = 0; y < height; y++) {
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data[y * width + x] = d[y];
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}
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}
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for (uint32_t y = 0; y < height; y++) {
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for (uint32_t x = 0; x < width; x++) {
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f[x] = data[y * width + x];
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}
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edt1d(f, d, v, z, width);
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for (uint32_t x = 0; x < width; x++) {
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data[y * width + x] = std::sqrt(d[x]);
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}
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}
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}
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} // namespace tinysdf
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AlphaImage transformRasterToSDF(const AlphaImage& rasterInput, double radius, double cutoff) {
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uint32_t size = rasterInput.size.width * rasterInput.size.height;
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uint32_t maxDimension = std::max(rasterInput.size.width, rasterInput.size.height);
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AlphaImage sdf(rasterInput.size);
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// temporary arrays for the distance transform
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std::vector<double> gridOuter(size);
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std::vector<double> gridInner(size);
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std::vector<double> f(maxDimension);
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std::vector<double> d(maxDimension);
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std::vector<double> z(maxDimension + 1);
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std::vector<int16_t> v(maxDimension);
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for (uint32_t i = 0; i < size; i++) {
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double a = static_cast<double>(rasterInput.data[i]) / 255; // alpha value
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gridOuter[i] = a == 1.0 ? 0.0 : a == 0.0 ? tinysdf::INF : std::pow(std::max(0.0, 0.5 - a), 2.0);
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gridInner[i] = a == 1.0 ? tinysdf::INF : a == 0.0 ? 0.0 : std::pow(std::max(0.0, a - 0.5), 2.0);
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}
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tinysdf::edt(gridOuter, rasterInput.size.width, rasterInput.size.height, f, d, v, z);
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tinysdf::edt(gridInner, rasterInput.size.width, rasterInput.size.height, f, d, v, z);
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for (uint32_t i = 0; i < size; i++) {
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double distance = gridOuter[i] - gridInner[i];
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sdf.data[i] = static_cast<uint8_t>(
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std::max(0l, std::min(255l, ::lround(255.0 - 255.0 * (distance / radius + cutoff)))));
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}
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return sdf;
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}
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} // namespace util
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} // namespace mbgl
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