Pure C++20 plotting API with pluggable backends for publication-ready IEEE/AIAA figures.

cmake --preset dev-debug
cmake --build --preset build-debug
ctest --preset test-debug

flowchart LR
  A[FigureSpec/AxesSpec/SeriesSpec] --> B[Figure/Axes Containers]
  B --> C[IPlotBackend]
  C --> D[GnuplotBackend]
  C --> E[SvgBackend]
  C --> J[PngBackend]
  D --> F[tmp/*.dat]
  D --> G[tmp/figure.gp]
  D --> H[figure.pdf|svg|eps|png]
  E --> I[figure.svg]
  J --> K[figure.png]

sequenceDiagram
  participant App as Example App (C++)
  participant Fig as gnuplotpp::Figure
  participant Be as Selected Backend

  App->>Fig: configure spec/layout + add series
  App->>Fig: save(out_dir)
  Fig->>Be: render(fig, out_dir)
  Be-->>Fig: RenderResult
  Fig-->>App: output paths

• dev-debug
• dev-release
• dev-cpm
• build-debug
• build-release
• build-cpm
• test-debug
• test-release

CPM is optional via GNUPLOTPP_ENABLE_CPM=ON. When enabled, CMake downloads CPM.cmake and resolves C++ libraries (nlohmann_json, fmt, spdlog). If network/package resolution fails, configuration now degrades with warnings and continues.

• CPM is best for CMake/C++ dependencies.
• gnuplot is an external CLI renderer.
• Recommended: install gnuplot with system package managers and keep CPM for C++ libs.

• RenderResult includes RenderStatus (Success, InvalidInput, IoError, ExternalToolMissing, ExternalToolFailure, UnsupportedFormat).
• Backends emit detailed file/tool failure messages and return explicit statuses.
• If fmt and spdlog are available (via CPM or system packages), the library uses them for structured formatting/logging.
• If not available, behavior falls back to standard C++ streams with the same status semantics.

You run only the C++ executable.

• If gnuplot exists, examples render publication outputs (pdf/svg/png) via GnuplotBackend.
• If gnuplot is missing, examples automatically fall back to native PngBackend and generate figure.png.
• If PNG fallback fails, examples try native SvgBackend as a secondary fallback.

./build/dev-debug/two_window_example --out out/two_window
./build/dev-debug/layout_2x2_example --out out/layout_2x2

Generated outputs include at least:

• out/<name>/figures/figure.png