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#include "terrain2.h"
#include <fstream>
TerrainMesh::TerrainMesh(const std::filesystem::path & input)
{
size_t ncols = 0, nrows = 0, xllcorner = 0, yllcorner = 0, cellsize = 0;
std::map<std::string_view, size_t *> properties {
{"ncols", &ncols},
{"nrows", &nrows},
{"xllcorner", &xllcorner},
{"yllcorner", &yllcorner},
{"cellsize", &cellsize},
};
std::ifstream f {input};
while (!properties.empty()) {
std::string property;
f >> property;
f >> *properties.at(property);
properties.erase(property);
}
std::vector<VertexHandle> vertices;
vertices.reserve(ncols * nrows);
for (size_t row = 0; row < nrows; ++row) {
for (size_t col = 0; col < ncols; ++col) {
float height = 0;
f >> height;
vertices.push_back(add_vertex({xllcorner + (col * cellsize), yllcorner + (row * cellsize), height}));
}
}
if (!f.good()) {
throw std::runtime_error("Couldn't read terrain file");
}
for (size_t row = 1; row < nrows; ++row) {
for (size_t col = 1; col < ncols; ++col) {
add_face({
vertices[ncols * (row - 1) + (col - 1)],
vertices[ncols * (row - 0) + (col - 0)],
vertices[ncols * (row - 0) + (col - 1)],
});
add_face({
vertices[ncols * (row - 1) + (col - 1)],
vertices[ncols * (row - 1) + (col - 0)],
vertices[ncols * (row - 0) + (col - 0)],
});
}
}
update_face_normals();
update_vertex_normals();
};
OpenMesh::FaceHandle
TerrainMesh::findPoint(glm::vec2 p) const
{
return findPoint(p, *faces_begin());
}
namespace {
[[nodiscard]] constexpr inline bool
pointLeftOfLine(const glm::vec2 p, const glm::vec2 e1, const glm::vec2 e2)
{
return (e2.x - e1.x) * (p.y - e1.y) > (e2.y - e1.y) * (p.x - e1.x);
}
static_assert(pointLeftOfLine({1, 2}, {1, 1}, {2, 2}));
static_assert(pointLeftOfLine({2, 1}, {2, 2}, {1, 1}));
static_assert(pointLeftOfLine({2, 2}, {1, 2}, {2, 1}));
static_assert(pointLeftOfLine({1, 1}, {2, 1}, {1, 2}));
[[nodiscard]] constexpr inline bool
linesCross(const glm::vec2 a1, const glm::vec2 a2, const glm::vec2 b1, const glm::vec2 b2)
{
return pointLeftOfLine(a2, b1, b2) && pointLeftOfLine(a1, b2, b1) && pointLeftOfLine(b1, a1, a2)
&& pointLeftOfLine(b2, a2, a1);
}
static_assert(linesCross({1, 1}, {2, 2}, {1, 2}, {2, 1}));
}
OpenMesh::FaceHandle
TerrainMesh::findPoint(glm::vec2 p, OpenMesh::FaceHandle f) const
{
ConstFaceVertexIter vertices;
while (f.is_valid() && !triangleContainsPoint(p, vertices = cfv_iter(f))) {
for (auto next = cfh_iter(f); next.is_valid(); ++next) {
f = opposite_face_handle(*next);
if (f.is_valid()) {
const auto e1 = point(to_vertex_handle(*next));
const auto e2 = point(to_vertex_handle(opposite_halfedge_handle(*next)));
if (pointLeftOfLine(p, e1, e2)) {
break;
}
}
f.reset();
}
}
return f;
}
void
TerrainMesh::walk(const glm::vec2 from, const glm::vec2 to, const std::function<void(FaceHandle)> & op) const
{
walkUntil(from, to, [&op](const auto & fh) {
op(fh);
return false;
});
}
void
TerrainMesh::walkUntil(const glm::vec2 from, const glm::vec2 to, const std::function<bool(FaceHandle)> & op) const
{
auto f = findPoint(from);
assert(f.is_valid()); // TODO replace with a boundary search
FaceHandle previousFace;
while (f.is_valid() && !op(f)) {
for (auto next = cfh_iter(f); next.is_valid(); ++next) {
f = opposite_face_handle(*next);
if (f.is_valid() && f != previousFace) {
const auto e1 = point(to_vertex_handle(*next));
const auto e2 = point(to_vertex_handle(opposite_halfedge_handle(*next)));
if (linesCross(from, to, e1, e2)) {
previousFace = f;
break;
}
}
f.reset();
}
}
}
bool
TerrainMesh::triangleContainsPoint(const glm::vec2 p, const glm::vec2 a, const glm::vec2 b, const glm::vec2 c)
{
const auto det = (b.x - a.x) * (c.y - a.y) - (b.y - a.y) * (c.x - a.x);
return det * ((b.x - a.x) * (p.y - a.y) - (b.y - a.y) * (p.x - a.x)) >= 0
&& det * ((c.x - b.x) * (p.y - b.y) - (c.y - b.y) * (p.x - b.x)) >= 0
&& det * ((a.x - c.x) * (p.y - c.y) - (a.y - c.y) * (p.x - c.x)) >= 0;
}
bool
TerrainMesh::triangleContainsPoint(const glm::vec2 p, FaceHandle face) const
{
return triangleContainsPoint(p, cfv_iter(face));
}
bool
TerrainMesh::triangleContainsPoint(const glm::vec2 p, ConstFaceVertexIter vertices) const
{
return triangleContainsPoint(p, point(*vertices++), point(*vertices++), point(*vertices++));
}
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