Use lower default exposure for movie tests

README.md

@@ -39,7 +39,7 @@ mkdir -p output/imgs
   --duration 2 --fps 30 --proper-acceleration 1.52
 ./build/minkowski_sky --observer-track output/minkowski_accel_2s.csv \
   --frames-dir output/imgs --frames-prefix minkowski_accel \
-  --start-time 0 --duration 2 --fps 30
+  --start-time 0 --duration 2 --fps 30 --exposure 1e-5
 ```
 
 This writes `minkowski_accel_000000.png` through
@@ -47,7 +47,10 @@ This writes `minkowski_accel_000000.png` through
 input; the acceleration generator is only a reproducible flat-spacetime test
 fixture.  The current movie path still renders frames independently while the
 time-slab/RayPool scheduler is implemented next, so it must not yet be used
-as a performance measurement for numerical-relativity data.
+as a performance measurement for numerical-relativity data.  Movie mode uses
+the same `1e-5` exposure by default when `--exposure` is omitted; this differs
+from the legacy single-frame default so the accelerated test catalog does not
+clip to white.
 
 PNG output is optional so the default build has no `libpng` dependency. Build
 with `make ENABLE_PNG=1`, then select it with a `.png` output path:

src/main.c

@@ -17,6 +17,7 @@ typedef struct {
   int width, height;
   int coarse_cell_pixels;
   int draw_mesh;
+  int exposure_was_set;
   double horizontal_fov_deg, look_ra_deg, look_dec_deg, exposure;
   double observer_inward_speed;
   PointSpreadFunction psf;
@@ -127,6 +128,7 @@ static int parse_args(int argc, char **argv, Settings *s,
                !parse_dec_deg(argv[++i], &s->look_dec_deg)) {
     } else if (!strcmp(argv[i], "--exposure") && i + 1 < argc &&
                !parse_positive(argv[++i], &s->exposure)) {
+      s->exposure_was_set = 1;
     } else if (!strcmp(argv[i], "--observer-inward-speed") && i + 1 < argc &&
                !parse_speed(argv[++i], &s->observer_inward_speed)) {
     } else if (!strcmp(argv[i], "--psf-fwhm-pixels") && i + 1 < argc &&
@@ -233,7 +235,14 @@ static int render_movie(const Settings *s, const StarCatalog *catalog,
                         const SpacetimeSource *spacetime) {
   ObserverTrack track = {0};
   Movie movie = {0};
+  Settings frame_settings = *s;
   int result = -1;
+  /* The single-image sky fixture historically used an exposure intended for
+   * static inspection.  A near-light-speed movie makes it clip immediately;
+   * retain that single-frame default but choose a legible, fixed test exposure
+   * for sequences unless the caller explicitly supplied --exposure. */
+  if (!frame_settings.exposure_was_set)
+    frame_settings.exposure = 1e-5;
   if (s->observer_track_path == NULL ||
       observer_track_load_csv(&track, s->observer_track_path) ||
       movie_init(&movie, &track, s->movie_start_time, s->movie_duration,
@@ -242,8 +251,8 @@ static int render_movie(const Settings *s, const StarCatalog *catalog,
   for (size_t i = 0; i < movie.frame_count; ++i) {
     char output_path[PATH_MAX];
     if (frame_output_path(output_path, s, movie.frames[i].frame_id) ||
-        render_observer_frame(s, catalog, spacetime, &movie.frames[i].observer,
-                              output_path))
+        render_observer_frame(&frame_settings, catalog, spacetime,
+                              &movie.frames[i].observer, output_path))
       goto done;
   }
   result = 0;