78ec33320f
some functions defined in <cmath>, as well as std::to_string aren't available on GNU's STL for some platforms, e.g. Android
94 lines
2.7 KiB
C++
94 lines
2.7 KiB
C++
#include <mbgl/util/tile_cover.hpp>
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#include <mbgl/util/vec.hpp>
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#include <mbgl/util/box.hpp>
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namespace mbgl {
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// Taken from polymaps src/Layer.js
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// https://github.com/simplegeo/polymaps/blob/master/src/Layer.js#L333-L383
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struct edge {
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double x0 = 0, y0 = 0;
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double x1 = 0, y1 = 0;
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double dx = 0, dy = 0;
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edge(vec2<double> a, vec2<double> b) {
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if (a.y > b.y) { std::swap(a, b); }
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x0 = a.x;
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y0 = a.y;
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x1 = b.x;
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y1 = b.y;
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dx = b.x - a.x;
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dy = b.y - a.y;
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}
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};
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typedef const std::function<void(int32_t x0, int32_t x1, int32_t y)> ScanLine;
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// scan-line conversion
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static void scanSpans(edge e0, edge e1, int32_t ymin, int32_t ymax, ScanLine scanLine) {
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double y0 = ::fmax(ymin, std::floor(e1.y0));
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double y1 = ::fmin(ymax, std::ceil(e1.y1));
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// sort edges by x-coordinate
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if ((e0.x0 == e1.x0 && e0.y0 == e1.y0) ?
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(e0.x0 + e1.dy / e0.dy * e0.dx < e1.x1) :
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(e0.x1 - e1.dy / e0.dy * e0.dx < e1.x0)) {
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std::swap(e0, e1);
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}
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// scan lines!
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double m0 = e0.dx / e0.dy;
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double m1 = e1.dx / e1.dy;
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double d0 = e0.dx > 0; // use y + 1 to compute x0
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double d1 = e1.dx < 0; // use y + 1 to compute x1
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for (int32_t y = y0; y < y1; y++) {
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double x0 = m0 * ::fmax(0, ::fmin(e0.dy, y + d0 - e0.y0)) + e0.x0;
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double x1 = m1 * ::fmax(0, ::fmin(e1.dy, y + d1 - e1.y0)) + e1.x0;
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scanLine(std::floor(x1), std::ceil(x0), y);
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}
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}
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// scan-line conversion
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static void scanTriangle(const mbgl::vec2<double> a, const mbgl::vec2<double> b, const mbgl::vec2<double> c, int32_t ymin, int32_t ymax, ScanLine& scanLine) {
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edge ab = edge(a, b);
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edge bc = edge(b, c);
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edge ca = edge(c, a);
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// sort edges by y-length
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if (ab.dy > bc.dy) { std::swap(ab, bc); }
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if (ab.dy > ca.dy) { std::swap(ab, ca); }
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if (bc.dy > ca.dy) { std::swap(bc, ca); }
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// scan span! scan span!
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if (ab.dy) scanSpans(ca, ab, ymin, ymax, scanLine);
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if (bc.dy) scanSpans(ca, bc, ymin, ymax, scanLine);
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}
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std::forward_list<TileID> tileCover(int8_t z, const mbgl::box &bounds, int8_t actualZ) {
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int32_t tiles = 1 << z;
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std::forward_list<mbgl::TileID> t;
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auto scanLine = [&](int32_t x0, int32_t x1, int32_t y) {
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int32_t x;
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if (y >= 0 && y <= tiles) {
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for (x = x0; x < x1; x++) {
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t.emplace_front(actualZ, x, y, z);
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}
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}
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};
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// Divide the screen up in two triangles and scan each of them:
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// \---+
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// | \ |
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// +---\.
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scanTriangle(bounds.tl, bounds.tr, bounds.br, 0, tiles, scanLine);
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scanTriangle(bounds.br, bounds.bl, bounds.tl, 0, tiles, scanLine);
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t.unique();
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return t;
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}
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}
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