Find and change entities

The drawing is plan.dxf, the one Read a drawing walks through, loaded as a value this time so it can change.

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auto loaded = DxfIO::LoadFile("plan.dxf");
if (!loaded)
{
  std::println("line {}: {}", loaded.error().Line, loaded.error().What);
  return 1;
}
DxfIO::Document &drawing = loaded->Document;
std::println("{} entities, {} issues", drawing.Entities.size(), loaded->Issues.size());

textCopy
29 entities, 0 issues

std::get_if gives a pointer to the entity when the variant holds that kind, and null otherwise. Record.Paper tells an entity of paper space from one of model space. Hex writes a handle as DXF does.

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for (DxfIO::Entity &one : drawing.Entities)
{
  DxfIO::Entities::Line *line = std::get_if<DxfIO::Entities::Line>(&one);
  if (line == nullptr || line->Record.Paper)
  {
    continue;
  }
  line->Start.X += 10;
  line->End.X += 10;
  std::println("LINE {} moved to ({}, {}) - ({}, {})", DxfIO::Hex(line->Record.Base.Self), line->Start.X,
               line->Start.Y, line->End.X, line->End.Y);
}

textCopy
LINE 2CE moved to (10, 0) - (110, 50)
LINE 2CF moved to (10, 0) - (20, 10)
LINE 2DA moved to (50, 0) - (50, 10)
LINE 2DB moved to (10, 20) - (40, 40)

Every kind dxfio types carries its layer and color in Record; an Unknown has none, and the requires test leaves it out. Edit::Same compares names as AutoCAD does, without case. Colors::Bylayer gives an entity its layer’s color; the circle on walls also has a true color in Rgb, cleared with it.

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for (DxfIO::Entity &one : drawing.Entities)
{
  std::visit(
      [&one](auto &kind) -> void
      {
        if constexpr (requires { kind.Record.Layer; })
        {
          DxfIO::Entities::Record &record = kind.Record;
          if (!DxfIO::Edit::Same(record.Layer.View(), "walls"))
          {
            return;
          }
          std::println("{} {} on walls: color {}, true color 0x{:06X}", DxfIO::TypeOf(one),
                       DxfIO::Hex(record.Base.Self), record.Color, record.Rgb.value_or(0));
          record.Color = DxfIO::Colors::Bylayer;
          record.Rgb.reset();
        }
      },
      one);
}

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CIRCLE 2D0 on walls: color 30, true color 0xFF8000

A handle’s Value is the number DXF writes in hex. Edit::FindEntity looks for it in the ENTITIES section and in every block, and returns a pointer into the document, or null. std::get_if gives null for a null pointer too, so one test covers both.

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DxfIO::Entity *found = DxfIO::Edit::FindEntity(drawing, DxfIO::Handle{.Value = 0x2D5});
if (auto *circle = std::get_if<DxfIO::Entities::Circle>(found))
{
  circle->Radius *= 2;
  std::println("CIRCLE 2D5 radius now {}", circle->Radius);
}

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CIRCLE 2D5 radius now 14

std::erase_if takes out of the list every entity the test picks and returns how many. It changes nothing else: a GROUP that lists a deleted entity in its Members would still name it. Nothing in plan.dxf names its points.

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const std::size_t deleted = std::erase_if(drawing.Entities, [](const DxfIO::Entity &one) -> bool
                                          { return std::holds_alternative<DxfIO::Entities::Point>(one); });
std::println("{} points deleted, {} entities left", deleted, drawing.Entities.size());

textCopy
3 points deleted, 26 entities left

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