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#pragma once
#include "../Common/Casts.hpp"
#include "../Math/Ray.hpp"
#include "Position.hpp"
namespace MC::World::VoxelTraversal {
// Amanatides, John, and Andrew Woo. 1987.
// "A Fast Voxel Traversal Algorithm for Ray Tracing."
// https://doi.org/10.2312/EGTP.19871000.
template <typename P>
Position::BlockWorld traverse(Ray ray, Real max_distance, P&& predicate) {
// Find the voxel grid cell containing the origin of the ray.
Position::BlockWorld block_pos = Position::World(ray.origin).round_to_block();
Position::BlockWorldOffset const step = {
Math::sign(ray.direction.x()),
Math::sign(ray.direction.y()),
Math::sign(ray.direction.z()),
};
Position::WorldOffset t_max = {
(TO(Real, block_pos.x()) + TO(Real, step.x() > 0) - ray.origin.x()) / ray.direction.x(),
(TO(Real, block_pos.y()) + TO(Real, step.y() > 0) - ray.origin.y()) / ray.direction.y(),
(TO(Real, block_pos.z()) + TO(Real, step.z() > 0) - ray.origin.z()) / ray.direction.z()
};
Position::WorldOffset const t_delta = {
TO(Real, step.x()) / ray.direction.x(),
TO(Real, step.y()) / ray.direction.y(),
TO(Real, step.z()) / ray.direction.z()
};
while (!predicate(block_pos)) {
// TODO: Calculate distance exactly.
if (ray.origin.distance(Vec3(block_pos)) > max_distance) return {};
if (t_max.x() < t_max.y()) {
if (t_max.x() < t_max.z()) {
block_pos.x() += step.x();
t_max.x() += t_delta.x();
} else {
block_pos.z() += step.z();
t_max.z() += t_delta.z();
}
} else {
if (t_max.y() < t_max.z()) {
block_pos.y() += step.y();
t_max.y() += t_delta.y();
} else {
block_pos.z() += step.z();
t_max.z() += t_delta.z();
}
}
}
return block_pos;
}
}
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