spec(t27f): deck -- a still shows the whole glass card (Closes #9985)

specs/t27f/deck.t27

@@ -117,6 +117,11 @@ pub const MIN_FOCUS_R_PX : i32 = 60;
 /// on screen while the camera moves under it.
 pub const FADE_OUT_FRAMES : i32 = 8;
 
+/// A still is one picture, not a video: nothing moves, so nothing fades. reel's still_frame is the
+/// last frame of a scene, where card_alpha is 0 -- a still drawn with card_alpha would show no card.
+/// Draw stills at the card's settled opacity instead.
+pub const STILL_CARD_ALPHA : i32 = 1000;
+
 /// The palette, 0xRRGGBB.
 pub const BACKDROP : i32 = 0x06060B;
 pub const AURORA_COUNT : i32 = 4;
@@ -592,6 +597,21 @@ test the_card_fades_and_never_pops {
     }
 }
 
+test a_still_shows_the_whole_card {
+    var n : i32 = MIN_SCENE_FRAMES;
+    while (n <= 300) {
+        // the still's card is the card the video shows once it has landed, never the faded one
+        assert STILL_CARD_ALPHA == card_alpha(TRANSITION_FRAMES, n);
+        assert STILL_CARD_ALPHA != card_alpha(n - 1, n);
+        var k : i32 = 0;
+        while (k < n) {
+            assert card_alpha(k, n) <= STILL_CARD_ALPHA;
+            k = k + 1;
+        }
+        n = n + 1;
+    }
+}
+
 test text_reads_on_glass {
     const under : i32 = worst_under_card();
     assert luma(TEXT) - under >= MIN_TEXT_CONTRAST;