feat(plot): nice-number ticks, axes, grid, traces, cursors, measurement queries

tests/test_measure.cpp

@@ -0,0 +1,43 @@
+#include "harness.hpp"
+#include <plot/plot/measure.hpp>
+#include <plot/data/array_series.hpp>
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+#include <vector>
+
+PLOT_TEST(measurement_over_interval_matches_direct_computation) {
+  std::vector<f32> y; for (int i = 0; i < 1000; ++i) y.push_back(f32(std::sin(static_cast<double>(i) * 0.01)));
+  plot::data::ArraySeries s(std::move(y), 0.0, 1.0);
+  const auto m = plot::Measure::evaluate(s, 100, 800);
+  double sum = 0, sumsq = 0, integral = 0; float lo = 1e30f, hi = -1e30f;
+  for (u64 i = 100; i < 800; ++i) {
+    const double v = std::sin(static_cast<double>(i) * 0.01);
+    sum += v; sumsq += v * v; integral += v;         // dx == 1
+    lo = std::min(lo, float(v)); hi = std::max(hi, float(v));
+  }
+  const double n = 700;
+  PLOT_CHECK_NEAR(m.mean, sum / n, 1e-5);
+  PLOT_CHECK_NEAR(m.rms, std::sqrt(sumsq / n), 1e-5);
+  PLOT_CHECK_NEAR(m.integral, integral, 1e-3);
+  PLOT_CHECK_NEAR(m.ymin, lo, 1e-6);
+  PLOT_CHECK_NEAR(m.ymax, hi, 1e-6);
+  PLOT_CHECK_NEAR(m.dx, 699.0, 1e-9);
+}
+PLOT_TEST(measurement_uses_pyramid_not_scan) {
+  // Guard against a future regression that linear-scans the series: a huge
+  // series must evaluate a 1-sample-wide interval in well under a millisecond.
+  std::vector<f32> y(1u << 22, 1.0f);              // 4M samples
+  plot::data::ArraySeries s(std::move(y), 0.0, 1.0);
+  const auto t0 = std::chrono::steady_clock::now();
+  for (int i = 0; i < 1000; ++i) (void)plot::Measure::evaluate(s, 1'000'000, 1'000'001);
+  const auto us = std::chrono::duration_cast<std::chrono::microseconds>(
+      std::chrono::steady_clock::now() - t0).count();
+  PLOT_CHECK(us < 50'000);                          // 1000 evals in < 50 ms
+}
+PLOT_TEST(empty_and_single_sample_intervals_are_valid_false) {
+  std::vector<f32> y{3.0f};
+  plot::data::ArraySeries s(std::move(y), 0.0, 1.0);
+  PLOT_CHECK(!plot::Measure::evaluate(s, 0, 0).valid);
+  PLOT_CHECK(!plot::Measure::evaluate(s, 1, 1).valid);
+}