Fog lit by rays: shadows cut through tiles, and walls stay visible

The fog asked one question per tile -- can I see its centre? -- and drew or
skipped the whole tile on the answer. Every shadow was a staircase, tiles
snapped in and out as you walked, and a wall beside you vanished whenever
its centre happened to sit behind its neighbour.

Visibility casts rays from the eye instead: a fixed sweep, plus two aimed
either side of every wall corner, which is what makes each shadow edge a
straight line rather than a smear between rays. The view now draws terrain
and actors first and then darkness over whatever the rays did not reach,
so a shadow runs straight through a tile and an enemy rounding a corner
appears a slice at a time. Bullets are a child node and are still drawn
over the dark; telegraphs are drawn after it, as they must be.

"A bit less strict" is three specific things. A wall face you can see is
lit 26 units in, measured perpendicular to the face; shadows end in a
short fade rather than a line; and sight fades over its last 64 units
rather than stopping at a circle. Still hard fog -- nothing remembered.

The first version measured that depth along the ray, and a screenshot
caught what no test had: a wall you look along got a sliver, so the wall
beside you in a tunnel looked missing -- the old fog's own complaint.
Perpendicular depth fixes it, and light stops the instant a ray steps
back into the open, so it never rounds a corner, never reaches the far
side of a one-tile wall, and never leaves a stepped wall through its
other face. Two tiles touching only at a corner are closed.

About half a millisecond a frame. Measured against the old fog in the
same scene: hub 68 fps against 62, dungeon 240 against 240. The hub's
own low rate predates this.

MapGrid gains a revision counter so the corner list is rebuilt only when
the map changes or the eye crosses a tile. screenshot.tscn now captures a
dungeon, a tunnel and the tunnel with F1's overlay, which draws where
each ray stopped -- and makes SHOT_DIR rather than failing every capture
when it does not exist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DECISIONS.md

@@ -89,6 +89,28 @@ about as often as a good one.
 **Hard fog.** *(User, this session.)* No remembered terrain — anything outside
 current line of sight is not drawn, including ground already walked over.
 
+**The fog is geometry, not a verdict per tile — and a little less strict.**
+*(User asked: "no longer grid based ... able to light up cells partially", and
+"a bit less strict". How strict was left to me.)* `Visibility` casts rays from
+the eye — a fixed sweep plus two aimed either side of every wall corner, which
+is what makes each shadow edge a straight line — and the view draws terrain and
+actors first, then darkness over everything the rays did not reach. A shadow
+edge runs straight through a tile; an enemy rounding a corner appears a slice
+at a time instead of popping in whole.
+
+"Less strict" is three specific things. The face of a wall you can see is lit
+26 units deep, measured perpendicular to the face — along the ray it was a
+sliver for any wall seen at a grazing angle, and the wall beside you vanished,
+which is the complaint the old fog had. Shadows end in an 8-unit fade instead
+of a hard line. And the edge of sight fades over its last 64 units instead of
+stopping at a circle. Nothing is remembered: still hard fog.
+
+Two lines this deliberately does not cross: light stops the moment a ray steps
+back out of the wall it was in, so it never rounds a corner or reaches the far
+side of a one-tile wall; and two blocking tiles that touch only at a corner are
+closed, not a crack. Bullets are drawn over the darkness, as they always were —
+a shot out of the black is still one you can dodge.
+
 **Dungeon size scales with depth.** *(User, this session.)* `--depth N` is a dev
 flag; what raises depth in actual play is still open.