Hatches

A hatch holds its boundary itself, as paths. Path flag 2 makes a polyline path, whose Vertices carry their bulges in Weight when Bulged is 1; flag 1 marks it external, and Closed 1 closes it.

C++Copy
DxfIO::Document drawing = DxfIO::Create(DxfIO::Version::R2018);

const auto traced = [](const DxfIO::Entities::LwPolyline &outline) -> DxfIO::Entities::Path
{
  DxfIO::Entities::Path path{};
  path.Flags = 1 | 2;
  path.Bulged = 1;
  path.Closed = 1;
  for (const DxfIO::Entities::LwPolyline::Vertex &one : outline.Vertices)
  {
    path.Vertices.push_back({.Position = one.Position, .Weight = one.Bulge});
  }
  return path;
};

A new hatch is a solid fill: the pattern named SOLID, with Solid 1 and, as AutoCAD writes it, Kind 1 for a predefined pattern. The hatch’s fields are in Fill, kept on the heap and reached with ->. Associative stays 0: the hatch keeps its own boundary and does not follow the polyline.

C++Copy
DxfIO::Entities::LwPolyline square{};
square.Flags = 1;
square.Vertices = {
    {.Position = {.X = 0, .Y = 0, .Z = 0}},
    {.Position = {.X = 40, .Y = 0, .Z = 0}},
    {.Position = {.X = 40, .Y = 40, .Z = 0}},
    {.Position = {.X = 0, .Y = 40, .Z = 0}},
};
DxfIO::Edit::Add(drawing, square);

DxfIO::Entities::Hatch solid{};
solid.Fill->Paths = {traced(square)};
DxfIO::Edit::Add(drawing, solid);

A pattern sets Solid to 0. A predefined pattern, Kind 1, is named in Name and drawn at Angle degrees and Scale. Stripes lists its families of lines as drawn: for ANSI31 at 45 degrees and scale 2, AutoCAD writes one family of lines at 90 degrees, each 6.35 from the next.

C++Copy
DxfIO::Entities::LwPolyline arch{};
arch.Flags = 1;
arch.Vertices = {
    {.Position = {.X = 60, .Y = 0, .Z = 0}},
    {.Position = {.X = 100, .Y = 0, .Z = 0}},
    {.Position = {.X = 100, .Y = 30, .Z = 0}, .Bulge = 1},
    {.Position = {.X = 60, .Y = 30, .Z = 0}},
};
DxfIO::Edit::Add(drawing, arch);

DxfIO::Entities::Hatch pattern{};
pattern.Fill->Name = "ANSI31";
pattern.Fill->Solid = 0;
pattern.Fill->Kind = 1;
pattern.Fill->Angle = 45;
pattern.Fill->Scale = 2;
pattern.Fill->Stripes = {{.Angle = 90, .X = 0, .Y = 0, .Run = -6.35, .Rise = 0, .Dashes = {}}};
pattern.Fill->Paths = {traced(arch)};
DxfIO::Edit::Add(drawing, pattern);

C++Copy
const auto saved = DxfIO::SaveFile(drawing, "hatch.dxf");
if (!saved)
{
  std::println("{}", saved.error().What);
  return 1;
}