Add observer track PNG movie mode

tests/test_geodesic.c

@@ -1,4 +1,5 @@
 #include "geodesic.h"
+#include "observer_track.h"
 
 #include <math.h>
 #include <stdio.h>
@@ -38,6 +39,24 @@ int main(void) {
   result = result || check_ray(&source, &look_at_ra_zero,
                                (double[]){1.0, 0.0, 0.0},
                                (double[]){1.0, 0.0, 0.0});
+  ObserverTrack accelerated = {0};
+  ObserverState final_observer;
+  if (observer_track_generate_minkowski_acceleration(&accelerated, 1.52, 2.0,
+                                                      1.0 / 30.0) ||
+      observer_track_interpolate(&accelerated, 2.0, &final_observer, NULL)) {
+    result = 1;
+  } else {
+    const RayEndpoint forward = geodesic_trace_past(
+        &source, &final_observer, (double[]){1.0, 0.0, 0.0},
+        &(GeodesicTraceConfig){.coordinate_time_step = 0.25, .max_steps = 100});
+    const double expected_g = sqrt(1.0 + 3.04 * 3.04) + 3.04;
+    if (forward.status != RAY_ENDPOINT_ESCAPED ||
+        !nearly_equal(forward.frequency_ratio, expected_g)) {
+      fputs("accelerated-observer Doppler regression failed\n", stderr);
+      result = 1;
+    }
+  }
+  observer_track_destroy(&accelerated);
   spacetime_destroy(&source);
   return result;
 }

tests/test_observer_track.c

@@ -0,0 +1,54 @@
+#include "movie.h"
+#include "observer_track.h"
+
+#include <math.h>
+#include <stdio.h>
+
+static int nearly_equal(double a, double b) { return fabs(a - b) < 1e-12; }
+
+int main(void) {
+  const char *path = "/tmp/gr_raytracing_observer_track.csv";
+  ObserverTrack generated = {0}, loaded = {0};
+  Movie movie = {0};
+  int result = 1;
+  if (observer_track_generate_minkowski_acceleration(&generated, 1.52, 2.0,
+                                                      1.0 / 30.0) ||
+      generated.count != 61 ||
+      !nearly_equal(generated.samples[60].coordinate_time, 2.0) ||
+      !nearly_equal(generated.samples[60].tetrad[0][0],
+                    sqrt(1.0 + 3.04 * 3.04)) ||
+      observer_track_write_csv(&generated, path) ||
+      observer_track_load_csv(&loaded, path) || loaded.count != generated.count ||
+      movie_init(&movie, &loaded, 0.0, 2.0, 30.0) || movie.frame_count != 61 ||
+      !nearly_equal(movie.frames[60].coordinate_time, 2.0) ||
+      !nearly_equal(movie.frames[60].observer.tetrad[0][3], -3.04))
+    goto done;
+  ObserverState interpolated;
+  double proper_time = 0.0;
+  if (observer_track_interpolate(&loaded, 1.0, &interpolated, &proper_time) ||
+      !nearly_equal(interpolated.coordinate_position[2],
+                    -(sqrt(1.0 + 1.52 * 1.52) - 1.0) / 1.52) ||
+      !nearly_equal(proper_time, asinh(1.52) / 1.52))
+    goto done;
+  {
+    FILE *bad = fopen(path, "w");
+    ObserverTrack invalid = {0};
+    if (bad == NULL)
+      goto done;
+    if (fputs("0,0,0\n", bad) < 0 || fclose(bad) != 0)
+      goto done;
+    if (observer_track_load_csv(&invalid, path) == 0) {
+      observer_track_destroy(&invalid);
+      goto done;
+    }
+  }
+  result = 0;
+done:
+  movie_destroy(&movie);
+  observer_track_destroy(&loaded);
+  observer_track_destroy(&generated);
+  remove(path);
+  if (result)
+    fputs("observer-track/movie regression failed\n", stderr);
+  return result;
+}