Layers

A new drawing has one layer, 0, and a new entity is on it.

C++Copy
DxfIO::Document drawing = DxfIO::Create(DxfIO::Version::R2018);
for (const DxfIO::Tables::Layer &layer : drawing.Layer.Records)
{
  std::println("{}: color {}, linetype {}, lineweight {}", layer.Record.Name, layer.Color, layer.Linetype,
               layer.Lineweight);
}

textCopy
0: color 7, linetype Continuous, lineweight -3

A Tables::Layer starts as layer 0 is: white (color 7), Continuous, plotted, at the drawing’s default lineweight (-3). Color is an AutoCAD Color Index from 1 to 255 and Lineweight is in hundredths of a millimeter. To give a layer a linetype other than Continuous, add the linetype to the LTYPE table: see Linetypes.

C++Copy
DxfIO::Tables::Layer walls{};
walls.Record.Name = "Walls";
walls.Color = 1;
walls.Lineweight = 50;
DxfIO::Edit::Add(drawing, walls);

DxfIO::Tables::Layer doors{};
doors.Record.Name = "Doors";
doors.Color = 3;
DxfIO::Edit::Add(drawing, doors);

Edit::Add fails when the table already holds a layer of that name. Names compare as AutoCAD compares them, without case.

C++Copy
DxfIO::Tables::Layer again{};
again.Record.Name = "WALLS";
const auto added = DxfIO::Edit::Add(drawing, again);
if (!added)
{
  std::println("{}", added.error().What);
}

textCopy
a record named WALLS is there already

Record.Layer names the entity’s layer. A color and lineweight left at ByLayer, as a new entity has them, are the layer’s. Edit::Add does not check that the layer exists; Audit::Check reports a layer an entity names that the table does not hold, and Audit::Repair makes it.

C++Copy
DxfIO::Entities::Line wall{};
wall.Record.Layer = DxfIO::Symbol{"Walls"};
wall.End = {.X = 400, .Y = 0, .Z = 0};
DxfIO::Edit::Add(drawing, wall);

DxfIO::Entities::Arc door{};
door.Record.Layer = DxfIO::Symbol{"Doors"};
door.Center = {.X = 100, .Y = 0, .Z = 0};
door.Radius = 90;
door.End = 90;
DxfIO::Edit::Add(drawing, door);

A layer is off when its color is negative: -8 is color 8, off. Record.Flags holds the rest as bits: 1 frozen, 2 frozen in new viewports, 4 locked. Plot false keeps a layer out of plots.

C++Copy
DxfIO::Tables::Layer grid{};
grid.Record.Name = "Grid";
grid.Color = -8;
grid.Plot = false;
DxfIO::Edit::Add(drawing, grid);

DxfIO::Tables::Layer survey{};
survey.Record.Name = "Survey";
survey.Color = 5;
survey.Record.Flags = 1 | 4;
DxfIO::Edit::Add(drawing, survey);

Edit::Find gives a pointer to the layer of that name, found without case, or null.

C++Copy
if (DxfIO::Tables::Layer *found = DxfIO::Edit::Find(drawing.Layer, "grid"))
{
  found->Color = -found->Color;
  std::println("{} is on, color {}", found->Record.Name, found->Color);
}

textCopy
Grid is on, color 8

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