sunlight through atmosphere

crates/resolved-cli/src/main.rs

@@ -189,6 +189,9 @@ fn render(args: &RenderArgs) -> Result<(), String> {
     let file = SceneFile::read(path)?;
     let dir = path.parent().unwrap_or(Path::new("."));
     let mut camera = file.camera(dir)?;
+    if let (LightingTier::L0, Some(exposure)) = (args.lighting, file.camera.exposure_l0) {
+        camera.exposure = exposure;
+    }
     if args.noiseless {
         camera.detector = camera.detector.noiseless();
     }

crates/resolved-cli/src/scene_file.rs

@@ -63,6 +63,10 @@ pub struct CameraFile {
     pub principal_point: Option<[f64; 2]>,
     pub f_number: Option<f64>,
     pub exposure: Option<f64>,
+    /// The exposure at lighting L0 in place of `exposure`, for a scene whose bodies L0
+    /// draws far brighter than L1 does (a lunar eclipse, which L0 draws without Earth's
+    /// shadow).
+    pub exposure_l0: Option<f64>,
     pub transmission: Option<f64>,
     pub gain: Option<f64>,
     pub bias: Option<f64>,
@@ -540,7 +544,7 @@ mod tests {
     #[test]
     fn camera_overrides_apply() {
         let file: SceneFile = toml::from_str(&format!(
-            "{MINIMAL}\n[camera]\nwidth = 640\nexposure = 2e-3\nadc_bits = 10\nread_noise = 2.5\n\
+            "{MINIMAL}\n[camera]\nwidth = 640\nexposure = 2e-3\nexposure_l0 = 5e-4\nadc_bits = 10\nread_noise = 2.5\n\
              dark_current = 0\nshot_noise = false\nprnu = 0.02\nhot_pixels = [1e-3, 20]\n\
              pattern_seed = 9\nblooming = {{ column = 0.25 }}\n"
         ))
@@ -548,6 +552,7 @@ mod tests {
         let camera = file.camera(Path::new(".")).unwrap();
         assert_eq!((camera.width, camera.height), (640, 1080));
         assert_eq!(camera.exposure, 2e-3);
+        assert_eq!(file.camera.exposure_l0, Some(5e-4));
         assert_eq!(camera.detector.adc_bits, 10);
         let d = camera.detector;
         assert_eq!(

crates/resolved-cli/tests/cli.rs

@@ -185,21 +185,24 @@ fn pretty_previews_lift_the_darks_and_leave_space_black() {
 
 #[cfg(feature = "astrokit")]
 #[test]
-fn lunar_eclipse_darkens_the_moon() {
-    // Mid-totality: at L1 the whole Moon is in Earth's umbra and reads the bias. At L0
-    // there are no eclipses on the bodies and it is a full Moon.
+fn lunar_eclipse_darkens_and_reddens_the_moon() {
+    // Mid-totality: at L1 the whole Moon is in Earth's umbra, lit only through Earth's
+    // atmosphere, red, and brighter at its northern edge, farther from the shadow's
+    // axis, than at its southern. At L0 there are no eclipses on the bodies, and the
+    // full Moon at the scene's L0 exposure, 300 times shorter, is bright but short of
+    // saturation.
     let scene = "examples/scenes/lunar-eclipse.toml";
     let l0 = render_at(scene, "gpu", "L0");
     let l1 = render_at(scene, "gpu", "L1");
-    assert!(
-        l0.get_pixel(960, 540).0.iter().all(|&v| v > 150),
-        "{:?}",
-        l0.get_pixel(960, 540)
-    );
-    assert!(
-        l1.pixels().all(|p| p.0 == [64; 3]),
-        "every pixel at the bias"
-    );
+    let full = l0.get_pixel(960, 540).0;
+    assert!(full.iter().all(|&v| v > 1000 && v < 4000), "{full:?}");
+    let [north, center, south] = [260, 540, 820].map(|y| l1.get_pixel(960, y).0);
+    // Measured: 695, 287, 145 DN at the north, 592, 164, 77 at the center, 208, 82, 65
+    // at the south, over a bias of 64.
+    for p in [north, center, south] {
+        assert!(p[0] > p[1] && p[1] >= p[2] && p[2] >= 64, "{p:?}");
+    }
+    assert!(north[0] > center[0] && center[0] > south[0] && south[0] > 100);
 }
 
 #[cfg(feature = "astrokit")]