Fog of war: unexplored is black, fades ease into it with no stepped rim (t17)

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

docs/DESIGN.md

@@ -239,6 +239,7 @@ above, including:
   the ground, so the owner couldn't see what was around them or where to dig.
   As tuned: clear to 12 grains, fading out by 24, with a grainy edge; the owner found the first
   version's narrow fade too sharp.
+  Unexplored ground is pure black, not dark grey (the owner: "should be black anyway").
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -221,7 +221,7 @@ World state: the per-cell typed arrays, alloc(), ambient temperature by depth, w
 - functions: emit, bagCap, discover, alloc, depthU, depthY, computeAmbient, fillNoise, wakeXY, wakeHeatXY, wakeIdx, wakeHeatIdx
 - variables: W, H, N, CW, CH, NCH, mat, temp, life, flags, stamp, part, mach, digp, noiseB, airS, netId, isPow, occ, surfY, dirtY, graniteY, basaltY, magmaY, roofY, AMB, worldSeed, surfBase, underD, shallowD, lapse, BW, BH, NB, blockP, blockV, ents, bgm, flyers, ghostBlocks, ghostMolds, awake, hot, hotLvl, tick, tickStamp, machines, molds, nets, pcells, powerDirty, beltL, beltR, tubeLists, brokenMachines, ghostMachines, ghostBlocked, EV, bot, bag, bagTotal, player, seen, ledger, stats
 
-### src/sim/fog.js (51 lines)
+### src/sim/fog.js (52 lines)
 Exploration only: never changes grains or the random stream.
 - functions: fogAlloc, fogMark, fogSeen, fogInit, fogLook, fogRevealAround, fogRevealAll
 - variables: FOG, FOG_SENSE, FOG_SENSE_FADE, fog, FW, FH
@@ -343,7 +343,7 @@ Drawing (src/render/): browser only. This file: the renderer state R, colour tab
 Propagated coloured light from glowing and burning cells.
 - functions: computeLight
 
-### src/render/world.js (299 lines)
+### src/render/world.js (304 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, drawWorld
 - variables: TUBE_CLASS

docs/agent-log.md

@@ -4,6 +4,18 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-24: t17 follow-up: no jagged rim, unexplored is black (Claude Code)
+
+- The owner still saw a jagged grey edge. Causes found by sampling pixels: the fade went to 0
+  (black) while unexplored was drawn (12, 10, 10), leaving a dark stepped rim; the ±40 noise lit
+  the faintest cells; rays that reached rock already dim dropped to 0 in 2–3 grains.
+- `src/render/world.js`: unexplored and off-map are pure black (`OUT`, smooth-look buffers);
+  partial fog eases into black along a smoothstep, with noise scaled by s·(1−s). `src/sim/fog.js`:
+  sight into rock fades over 8 grains as a fraction of its brightness.
+- `test/play.py`: the three unexplored-colour checks expect black (owner's decision).
+  `docs/systems/fog.md` updated. Screenshots `shots/fog-dig-black-{pixel,smooth,nolight}.png`.
+- Tests: `run_all.py --browser` passed except `t_smooth` once at load 7 (passed on rerun).
+
 ## 2026-10-24: t17 follow-up: softer fog edges (Claude Code, Codex)
 
 - The owner found the edges sharp and stepped. `src/sim/fog.js`: sense ring 24 grains with a

docs/systems/fog.md

@@ -28,10 +28,10 @@ immediately from the bot.
 
 ## Drawing and setting
 
-Both looks and the thermal lens sample fog bilinearly. Partial values get stable per-grain
-noise of about ±40, clamped to 1–255, to break up stepped edges. Unseen and fully seen
-grains are unchanged. Seen grains use the usual drawing;
-unseen grains use the out-of-world colour and smooth-look buffers, hiding their shapes.
+Both looks and the thermal lens sample fog bilinearly. Partly seen grains darken toward black
+along a smoothstep curve, with stable per-grain noise (up to about ±38 mid-fade, none at either
+end) to break up the half-resolution steps. Fully seen grains use the usual drawing; unseen
+grains are pure black (as is everything off the map) in both looks, hiding their shapes.
 Partial values dim foreground, background and trees. Bloom sources need at least 128;
 bars, flyers, rain and particles need at least 64. Hover info and the cursor label say
 only “Unexplored” below 64.

src/render/world.js

@@ -23,7 +23,7 @@ function drawWorld() {
     }
   }
   const useFog = SET.fog;
-  const OUT = sm ? 0x040a0a0c : 0xff0a0a0c;
+  const OUT = sm ? 0x04000000 : 0xff000000; // unexplored and off the map: black
   const lighting = SET.lighting !== 'off' && !R.lens;
   if (lighting && (R.frame % SET.lightEvery === 0 || !R.lw)) computeLight();
   const grain = SET.grain, incand = SET.incandescence;
@@ -35,22 +35,27 @@ function drawWorld() {
   for (let by = 0; by < bh; by++) {
     const y = vy0 + by;
     const row = by * bw;
-    if (y < 0 || y >= H) { for (let bx = 0; bx < bw; bx++) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0x000a0a0c; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } } continue; }
+    if (y < 0 || y >= H) { for (let bx = 0; bx < bw; bx++) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } } continue; }
     const fy = y / FOG, fj = Math.floor(fy), ft = fy - fj, fr = fj * FW, fn = Math.min(FH - 1, fj + 1) * FW;
     const yw = y * W;
     let skr = SKY_R[y], skg = SKY_G[y], skb = SKY_B[y];
     if (rk > 0.01) { const gy = (skr + skg + skb) / 3 * 0.82; skr += (gy - skr) * rk * 0.7; skg += (gy - skg) * rk * 0.7; skb += (gy - skb) * rk * 0.65; }
     for (let bx = 0; bx < bw; bx++) {
       const x = vx0 + bx;
-      if (x < 0 || x >= W) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0x000a0a0c; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } continue; }
+      if (x < 0 || x >= W) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } continue; }
       let fv = 255;
       if (useFog) {
         const fx = x / FOG, j = Math.floor(fx), t = fx - j, j1 = Math.min(FW - 1, j + 1);
         const a = fog[fr + j], b = fog[fr + j1], c = fog[fn + j], d = fog[fn + j1];
         if ((a & b & c & d) !== 255) fv = (a + (b - a) * t) * (1 - ft) + (c + (d - c) * t) * ft;
-        if (!fv) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0x000a0a0c; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } continue; }
-        // Stable grain noise breaks up the half-resolution fog's stepped edges.
-        if (fv < 255) fv = Math.max(1, Math.min(255, fv + (noiseB[yw + x] - 128) * (40 / 128)));
+        if (!fv) { px[row + bx] = OUT; if (sm) { bpx[row + bx] = 0; tpx[row + bx] = 0; fpx[row + bx] = 0xff; } continue; }
+        // ease the fade into black (smoothstep) and break up the half-resolution steps with grain
+        // noise that is strongest mid-fade and nothing at either end, so the outer edge has no rim
+        if (fv < 255) {
+          let s = fv / 255;
+          s = Math.min(1, Math.max(0, s + (noiseB[yw + x] - 128) * (0.6 / 128) * s * (1 - s)));
+          fv = Math.max(1, 255 * s * s * (3 - 2 * s));
+        }
       }
       const i = yw + x, m = mat[i], nz = noiseB[i] - 128;
       const T = temp[i];

src/sim/fog.js

@@ -25,7 +25,8 @@ function fogLook(cx, cy) {
       if (x < 0 || y < 0 || x >= W || y >= H) break;
       const ph = PH[mat[y * W + x]];
       if (hit < 0 && (ph === PH_SOLID || ph === PH_POWDER)) hit = d;
-      const v = Math.min(255, (48 - d) * 255 / 16, hit < 0 ? 255 : (8 - d + hit) * 255 / 8);
+      // into rock, sight fades out over 8 grains from however bright it arrived
+      const v = Math.min(255, (48 - d) * 255 / 16) * (hit < 0 ? 1 : (8 - d + hit) / 8);
       if (v <= 0) break;
       fogMark(x, y, v);
     }

test/play.py

@@ -807,7 +807,7 @@ with sync_playwright() as p:
     }""")
     fp.wait_for_timeout(300)
     sample = "(() => { drawWorld(); const k = (235 - R.vy0) * R.bw + 300 - R.vx0; return R.px[k] & 0xffffff; })()"
-    check('unexplored pixel is out-of-world black', fp.evaluate(sample) == 0x0a0a0c)
+    check('unexplored pixel is black', fp.evaluate(sample) == 0)
     check('sky starts seen and draws colour', fp.evaluate("(() => { const cy=R.camY; R.camY=0; drawWorld(); const c=R.px[20*R.bw+20]&0xffffff; R.camY=cy; drawWorld(); return fogSeen(300,0)===255 && c!==0x0a0a0c; })()"))
     check('unexplored canvas pixel is black', fp.evaluate("(() => {const s=worldToScreenPx(300.5,235.5);return Array.from(R.ctx.getImageData(s.x,s.y,1,1).data).slice(0,3).every(v=>v<=12)})()"))
     check('hover and cursor share only Unexplored', fp.evaluate("JSON.stringify(hoverInfo(300,235)) === JSON.stringify({t1:'Unexplored',t2:[],t3:[]})"))
@@ -821,13 +821,13 @@ with sync_playwright() as p:
     }"""))
     fp.screenshot(path=str(out / 'fog-pixel.png'))
     fp.evaluate('R.lens = true')
-    check('thermal lens hides unexplored grains', fp.evaluate(sample) == 0x0a0a0c)
+    check('thermal lens hides unexplored grains', fp.evaluate(sample) == 0)
     fp.evaluate('R.lens = false; SET.fog = false')
-    check('fog toggle shows the same rock', fp.evaluate(sample) != 0x0a0a0c)
+    check('fog toggle shows the same rock', fp.evaluate(sample) != 0)
     fp.evaluate("SET.fog = true; SET.look = 'smooth'; SM.t0 = performance.now() + 100000")
     fp.wait_for_timeout(500)
     check('fog draws in the smooth look', fp.evaluate('R.smoothOn && SM.ok'))
-    check('unseen smooth grains have no terrain shape', fp.evaluate("(() => {const k=(235-R.vy0)*R.bw+300-R.vx0;return R.px[k]===0x040a0a0c && R.backPx[k]===0x000a0a0c && R.treePx[k]===0 && R.fieldPx[k]===255})()"))
+    check('unseen smooth grains have no terrain shape', fp.evaluate("(() => {const k=(235-R.vy0)*R.bw+300-R.vx0;return R.px[k]===0x04000000 && R.backPx[k]===0 && R.treePx[k]===0 && R.fieldPx[k]===255})()"))
     fp.screenshot(path=str(out / 'fog-smooth.png'))
     fb.close()