plotter/README.md

# plot

An embeddable OpenGL time-series plotting library for real-time, high-sample-rate data.
The core (`plot::core`, C++20, OpenGL 3.3 core) has no third-party dependency at all;
the host integrations that own a window and an event loop are separate, opt-in targets
built on top of it.

## Hosts, and what a frame costs

| host | CMake target | source |
|---|---|---|
| GLFW | `plot::glfw` | `adapters/glfw/` |
| Dear ImGui | `plot::imgui` (build-tree only) | `adapters/imgui/` |
| Qt6 | `plot::qt6` | `adapters/qt6/` |
| GTK4 | `plot::gtk4` | `adapters/gtk4/` |

Per-frame rendering cost is O(visible pixels + samples produced since the last frame),
not O(samples): a trace denser than one sample per pixel is drawn from a min/max LOD
pyramid rather than from raw samples. The `plot_multiplot_demo` run stages **18,651 GPU
segments** to draw **~4.5 million visible samples** across six traces — the frame is
bounded by the pixels it lights, not by the sample count behind them. That figure is from
a `linux-release` build under `xvfb-run` on **llvmpipe** (Mesa's software rasteriser); no
run touched a GPU, so read it as an upper bound and a record of the software path.

## Features

- grid with independent major/minor line classes (`Style::grid_major_visible`,
  `grid_minor_visible`);
- x and y axes, with a vertical (bottom-to-top) y-axis title;
- cursors in both orientations — vertical markers and horizontal rulers;
- draggable regions and measurement bands with exact interval statistics;
- a signal legend anchored to an axes corner;
- a hover crosshair with a per-signal, interpolated readout;
- a multi-plot `Figure` of stacked rows sharing one synchronised x axis;
- live follow (`XFollow::Live`) with relative (multiplicative) zoom and mouse panning;
- DPI-consistent sizing: metrics are logical units converted once through
  `Style::ui_scale`;
- an anti-aliased embedded monospaced font, plus an optional runtime TrueType backend
  (`plot::font_ttf`).

## Build and install

Needs a C++20 compiler and CMake **3.24+**. Presets live in `CMakePresets.json`
(`linux-debug`, `linux-release`, `linux-asan`, `linux-coverage`).

```sh
cmake --preset linux-release
cmake --build build/release
cmake --install build/release --prefix /where/you/want
```

Install is on by default (`PLOT_INSTALL=ON`) and installs the `plot_core` archive, the
public headers under `include/plot/`, and a CMake package config under `lib/cmake/plot/`.
A consumer then needs only:

```cmake
find_package(plot 0.1 REQUIRED)
target_link_libraries(my_app PRIVATE plot::core)
```

## Embedding

A host owns the window, the GL context and the event loop; `plot` owns none of them. This
is the whole of a minimal GLFW program — the adapter opens the window, runs the loop and
feeds the controller, and the callback is where live data would be pushed:

```cpp
#include <glfw/glfw_host.hpp>   // the optional GLFW adapter
#include <plot/plot.hpp>

#include <cmath>
#include <vector>

int main() {
  plot::glfw::Host host;
  plot::Plot& p = host.plot();

  std::vector<plot::f32> y(512);
  for (plot::usize i = 0; i < y.size(); ++i)
    y[i] = static_cast<plot::f32>(std::sin(0.05 * static_cast<double>(i)));
  plot::data::ArraySeries series(std::move(y), 0.0, 1.0);

  const plot::u32 x = p.add_x_axis({"x", {0.0, 511.0}, true});
  const plot::u32 sig = p.add_y_axis({"signal", {-1.0, 1.0}, true, plot::AxisPlace::Left});
  p.add_trace({&series, plot::Color::hex(0x4FA3FF), 1.5f, x, sig, "sine"});

  plot::Status st;
  return host.run({800, 480, "plot"}, [](plot::Plot&, plot::f64) {}, &st) ? 0 : 1;
}
```

It compiles and links against a built tree (see [docs/getting-started.md](docs/getting-started.md)
for the same program written against `plot::core` directly, with no adapter):

```sh
g++ -std=c++20 -I include -I adapters readme_main.cpp \
    build/debug/adapters/glfw/libplot_glfw.a build/debug/libplot_core.a \
    $(pkg-config --libs glfw3) -ldl -lpthread -o plot_readme
```

## Documentation

The user guide lives under `docs/`; `docs/superpowers/` is the design record, not user
documentation.

- [Getting started](docs/getting-started.md) — prerequisites, build/install/consume, and a
  minimal GLFW program against `plot::core`.
- [Architecture](docs/architecture.md) — the layers (`core`/`math` → `gl` → `data` →
  `render` → `plot` → `input`), what each owns, and the dependency rules.
- [Embedding into a host](docs/embedding.md) — the four adapters, the `ui_scale`/DPI rule
  per host, and the headless demo invocations.
- [Data and performance](docs/data-and-performance.md) — the sample stores, the
  single-producer/single-consumer contract, the LOD pyramid, and the measured frame times.
- [Interaction](docs/interaction.md) — cursors, regions, the measurement band, the legend,
  the crosshair, the gesture table, and live follow.
- [Styling](docs/styling.md) — every `Style` field with its default and unit, the grid
  classes, and installing a text backend.
- [Building and testing](docs/building-and-testing.md) — presets, `PLOT_BUILD_*` options,
  the suite, the headless demo modes, and the coverage command.
- [Coverage](docs/coverage.md) — the coverage method and the measured per-file table.

## Testing and coverage

```sh
cmake --preset linux-debug
cmake --build build/debug
ctest --test-dir build/debug --output-on-failure   # 283 cases, 0 failed

tools/coverage.sh                                  # configure+build+run+capture+floor check
```

The `linux-debug` suite runs **283 cases**; the `linux-coverage` preset builds **272** of
them, because its adapters are off and 11 cases need an adapter target (8 in
`test_imgui_widget.cpp`, 3 in `test_glfw_host.cpp`). Coverage is enforced by
`tools/coverage.sh` against `tools/coverage_floor.py`: **80%** per file under `src/` and
**90%** aggregate. The current measurement is an aggregate **95.3% (3284/3447 lines)** over
23 files, every file at or above 80%; the per-file table is in
[docs/coverage.md](docs/coverage.md), which the command regenerates.

## Licence and third-party provenance

- **This library** is **MIT licensed**: the full text is in [`LICENSE`](LICENSE), and
  every first-party file (C++, Python and shell) carries its SPDX identifier in the file
  header — `// SPDX-License-Identifier: MIT` — so the grant travels with each source file,
  not just the repository root.
- **Adwaita Mono** (the embedded font, `render::EmbeddedMonoFont`) is under **SIL OFL
  1.1**, committed verbatim at [`licences/OFL-1.1.txt`](licences/OFL-1.1.txt). The backend
  class is named neutrally (`EmbeddedMonoFont`, not "Adwaita Mono") because OFL reserves
  the font name for modified redistributions. The baked atlas is generated at authoring
  time by `tools/fonts/gen_atlas.py` and committed as data, so `plot_core` rasterises
  nothing at build or run time.
- **stb_truetype v1.26** (public domain, Sean Barrett / RAD Game Tools) is vendored at
  `third_party/stb_truetype.h` and compiled **only** by the optional `plot_font_ttf`
  target; its include directory is `PRIVATE`, so no consumer and no other target can reach
  it. `PLOT_BUILD_TTF_FONT` defaults on exactly when the vendored header is present.
- **`plot_core` is third-party-free.** It links only `${CMAKE_DL_LIBS}`, and no public
  header under `include/plot/` includes a third-party header. The header self-containment
  and umbrella checks in `tests/CMakeLists.txt` fail the build if either rule breaks.

## Limitations

- **Timings are llvmpipe under Xvfb** (`tools/coverage.sh`, the demo summaries). No
  measurement here used a GPU; there are no hardware numbers.
- **macOS and Windows are untested.** Development and CI are Linux/EGL + X11 only.
- **Fractional-scale compositing and touchpad scroll calibration are unverified** — the
  `ui_scale` sources are correct per host, but no run exercised a real fractional DPI or a
  calibrated scroll device.
- **Untrusted font files are out of scope** for the runtime `plot::font_ttf` backend:
  stb_truetype does no range checking, so `from_file()` must only be handed files the host
  trusts.
- **`render` ↔ `plot` is not a strict include chain.** `Renderer` includes `plot/plot.hpp`
  because drawing *is* being handed a `Plot`; the `plot` layer names only `render`'s value
  types (`Style`, `TextBackend`), never `Renderer`. The cycle and its direction are
  documented in [docs/architecture.md](docs/architecture.md).