stl_import_ascii_reader.cc

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/* SPDX-FileCopyrightText: 2023 Blender Authors
 *
 * SPDX-License-Identifier: GPL-2.0-or-later */
 
#include <cstdio>
#include <system_error>
 
#include "BLI_fileops.hh"
#include "BLI_math_vector_types.hh"
#include "BLI_memory_utils.hh"
 
#include "DNA_mesh_types.h"
 
/* NOTE: we could use C++17 <charconv> from_chars to parse
 * floats, but even if some compilers claim full support,
 * their standard libraries are not quite there yet.
 * LLVM/libc++ only has a float parser since LLVM 14,
 * and gcc/libstdc++ since 11.1. So until at least these are
 * the minimum spec, use an external library. */
#include "fast_float.h"
 
#include "stl_data.hh"
#include "stl_import_ascii_reader.hh"
#include "stl_import_mesh.hh"
 
namespace blender::io::stl {
 
class StringBuffer {
 private:
  char *start;
  const char *end;
 
 public:
  StringBuffer(char *buf, size_t len)
  {
    start = buf;
    end = start + len;
  }
 
  bool is_empty() const
  {
    return start == end;
  }
 
  void drop_leading_control_chars()
  {
    while ((start < end) && (*start) <= ' ') {
      start++;
    }
  }
 
  void drop_leading_non_control_chars()
  {
    while ((start < end) && (*start) > ' ') {
      start++;
    }
  }
 
  void drop_line()
  {
    while (start < end && *start != '\n') {
      start++;
    }
  }
 
  bool parse_token(const char *token, size_t token_length)
  {
    drop_leading_control_chars();
    if (end - start < token_length + 1) {
      return false;
    }
    if (memcmp(start, token, token_length) != 0) {
      return false;
    }
    if (start[token_length] > ' ') {
      return false;
    }
    start += token_length + 1;
    return true;
  }
 
  void drop_token()
  {
    drop_leading_non_control_chars();
    drop_leading_control_chars();
  }
 
  void parse_float(float &out)
  {
    drop_leading_control_chars();
    /* Skip '+' */
    if (start < end && *start == '+') {
      start++;
    }
    fast_float::from_chars_result res = fast_float::from_chars(start, end, out);
    if (ELEM(res.ec, std::errc::invalid_argument, std::errc::result_out_of_range)) {
      out = 0.0f;
    }
    start = const_cast<char *>(res.ptr);
  }
};
 
static inline void parse_float3(StringBuffer &buf, float3 &out)
{
  for (int i = 0; i < 3; i++) {
    buf.parse_float(out[i]);
  }
}
 
Mesh *read_stl_ascii(const char *filepath, const bool use_custom_normals)
{
  size_t buffer_len;
  void *buffer = BLI_file_read_text_as_mem(filepath, 0, &buffer_len);
  if (buffer == nullptr) {
    fprintf(stderr, "STL Importer: cannot read from ASCII STL file: '%s'\n", filepath);
    return nullptr;
  }
  BLI_SCOPED_DEFER([&]() { MEM_freeN(buffer); });
 
  constexpr int num_reserved_tris = 1024;
 
  StringBuffer str_buf(static_cast<char *>(buffer), buffer_len);
  STLMeshHelper stl_mesh(num_reserved_tris, use_custom_normals);
 
  PackedTriangle data{};
  str_buf.drop_line(); /* Skip header line */
  while (!str_buf.is_empty()) {
    if (str_buf.parse_token("vertex", 6)) {
      parse_float3(str_buf, data.vertices[0]);
      if (str_buf.parse_token("vertex", 6)) {
        parse_float3(str_buf, data.vertices[1]);
      }
      if (str_buf.parse_token("vertex", 6)) {
        parse_float3(str_buf, data.vertices[2]);
      }
 
      stl_mesh.add_triangle(data);
    }
    else if (str_buf.parse_token("facet", 5)) {
      str_buf.drop_token(); /* Expecting "normal" */
      parse_float3(str_buf, data.normal);
    }
    else {
      str_buf.drop_token();
    }
  }
 
  return stl_mesh.to_mesh();
}
 
}  // namespace blender::io::stl