raytrace_line_2d.hpp

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// Author: Eitan Marder-Eppstein
//         David V. Lu!!
 
#ifndef NAV2_UTIL__RAYTRACE_LINE_2D_HPP_
#define NAV2_UTIL__RAYTRACE_LINE_2D_HPP_
 
#include <limits.h>
#include <algorithm>
#include <cmath>
 
namespace nav2_util
{
 
inline int sign(int x)
{
  return x > 0 ? 1 : -1;
}
 
template<class ActionType>
inline void bresenham2D(
  ActionType at, unsigned int abs_da, unsigned int abs_db, int error_b,
  int offset_a, int offset_b, unsigned int offset,
  unsigned int max_length)
{
  unsigned int end = std::min(max_length, abs_da);
  for (unsigned int i = 0; i < end; ++i) {
    at(offset);
    offset += offset_a;
    error_b += abs_db;
    if ((unsigned int)error_b >= abs_da) {
      offset += offset_b;
      error_b -= abs_da;
    }
  }
  at(offset);
}
 
template<class ActionType>
inline void raytraceLine(
  ActionType at, unsigned int x0, unsigned int y0, unsigned int x1,
  unsigned int y1, unsigned int step_x,
  unsigned int max_length = UINT_MAX, unsigned int min_length = 0)
{
  int dx_full = x1 - x0;
  int dy_full = y1 - y0;
 
  // we need to chose how much to scale our dominant dimension,
  // based on the maximum length of the line
  double dist = std::hypot(dx_full, dy_full);
  if (dist < min_length) {
    return;
  }
 
  unsigned int min_x0, min_y0;
  if (dist > 0.0) {
    // Adjust starting point and offset to start from min_length distance
    min_x0 = (unsigned int)(x0 + dx_full / dist * min_length);
    min_y0 = (unsigned int)(y0 + dy_full / dist * min_length);
  } else {
    // dist can be 0 if [x0, y0]==[x1, y1].
    // In this case only this cell should be processed.
    min_x0 = x0;
    min_y0 = y0;
  }
  unsigned int offset = min_y0 * step_x + min_x0;
 
  int dx = x1 - min_x0;
  int dy = y1 - min_y0;
 
  unsigned int abs_dx = abs(dx);
  unsigned int abs_dy = abs(dy);
 
  int offset_dx = sign(dx);
  int offset_dy = sign(dy) * step_x;
 
  double scale = (dist == 0.0) ? 1.0 : std::min(1.0, max_length / dist);
  // if x is dominant
  if (abs_dx >= abs_dy) {
    int error_y = abs_dx / 2;
 
    bresenham2D(
      at, abs_dx, abs_dy, error_y, offset_dx, offset_dy, offset, (unsigned int)(scale * abs_dx));
    return;
  }
 
  // otherwise y is dominant
  int error_x = abs_dy / 2;
 
  bresenham2D(
    at, abs_dy, abs_dx, error_x, offset_dy, offset_dx, offset, (unsigned int)(scale * abs_dy));
}
 
}  // namespace nav2_util
 
#endif  // NAV2_UTIL__RAYTRACE_LINE_2D_HPP_