1 files changed, 160 insertions, 0 deletions
diff --git a/source/blender/io/stl/importer/stl_import_ascii_reader.cc b/source/blender/io/stl/importer/stl_import_ascii_reader.cc
new file mode 100644
index 00000000000..2edb3c6a114
--- /dev/null
+++ b/source/blender/io/stl/importer/stl_import_ascii_reader.cc
@@ -0,0 +1,160 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup stl
+ */
+
+#include <cstdint>
+#include <cstdio>
+
+#include "BKE_mesh.h"
+
+#include "BLI_fileops.hh"
+#include "BLI_memory_utils.hh"
+#include "BLI_string_ref.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_import.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 (res.ec == std::errc::invalid_argument || res.ec == std::errc::result_out_of_range) {
+      out = 0.0f;
+    }
+    start = const_cast<char *>(res.ptr);
+  }
+};
+
+static inline void parse_float3(StringBuffer &buf, float out[3])
+{
+  for (int i = 0; i < 3; i++) {
+    buf.parse_float(out[i]);
+  }
+}
+
+Mesh *read_stl_ascii(const char *filepath, Main *bmain, char *mesh_name, 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 BKE_mesh_add(bmain, mesh_name);
+  }
+  BLI_SCOPED_DEFER([&]() { MEM_freeN(buffer); });
+
+  int num_reserved_tris = 1024;
+
+  StringBuffer str_buf(static_cast<char *>(buffer), buffer_len);
+  STLMeshHelper stl_mesh(num_reserved_tris, use_custom_normals);
+  float triangle_buf[3][3];
+  float custom_normal_buf[3];
+  str_buf.drop_line(); /* Skip header line */
+  while (!str_buf.is_empty()) {
+    if (str_buf.parse_token("vertex", 6)) {
+      parse_float3(str_buf, triangle_buf[0]);
+      if (str_buf.parse_token("vertex", 6)) {
+        parse_float3(str_buf, triangle_buf[1]);
+      }
+      if (str_buf.parse_token("vertex", 6)) {
+        parse_float3(str_buf, triangle_buf[2]);
+      }
+      if (use_custom_normals) {
+        stl_mesh.add_triangle(
+            triangle_buf[0], triangle_buf[1], triangle_buf[2], custom_normal_buf);
+      }
+      else {
+        stl_mesh.add_triangle(triangle_buf[0], triangle_buf[1], triangle_buf[2]);
+      }
+    }
+    else if (str_buf.parse_token("facet", 5)) {
+      str_buf.drop_token(); /* Expecting "normal" */
+      parse_float3(str_buf, custom_normal_buf);
+    }
+    else {
+      str_buf.drop_token();
+    }
+  }
+
+  return stl_mesh.to_mesh(bmain, mesh_name);
+}
+
+}  // namespace blender::io::stl