Throughput in the info overlay: grains per second and backing-up glow (t49)

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

src/sim/flow.js

@@ -0,0 +1,26 @@
+// Throughput for the info overlay (t49): how many grains each belt, filter and screw conveyor
+// block hands on, per second of game time. Counting runs only while the overlay is on, so
+// normal play pays one flag check per carried grain. Bars are not counted.
+let flowOn = false, flowCount = new Uint16Array(0), flowRate = new Float32Array(0);
+function setFlowCounting(on) {
+  flowOn = on;
+  if (flowCount.length !== NB) { flowCount = new Uint16Array(NB); flowRate = new Float32Array(NB); }
+  else if (!on) { flowCount.fill(0); flowRate.fill(0); }
+}
+// A grain left carrier block b across one of its edges.
+function flowNote(b) { if (b >= 0 && b < flowCount.length && flowCount[b] < 65535) flowCount[b]++; }
+// Count a move from cell a to cell j if it crosses into another column of blocks or row of blocks.
+function flowCross(b, a, j) { if (((a % W) >> 2) !== ((j % W) >> 2) || ((a / W) >> 2) !== ((j / W) >> 2)) flowNote(b); }
+// The sloped belt block carrying a grain at cell a: the slope under it in the same block column.
+function flowSlopeUnder(a) {
+  const bx = (a % W) >> 2;
+  for (let by = ((a / W) | 0) >> 2, k = 0; k < 3 && by < BH; k++, by++) if (isSlopeBelt(blockP[by * BW + bx])) return by * BW + bx;
+  return -1;
+}
+// Once a second, fold the count into a smoothed rate.
+function flowTick() {
+  if (flowCount.length !== NB) setFlowCounting(flowOn);
+  if (tick % 60) return;
+  for (let b = 0; b < NB; b++) { if (flowCount[b] || flowRate[b]) { flowRate[b] = flowRate[b] * 0.5 + flowCount[b] * 0.5; if (flowRate[b] < 0.05) flowRate[b] = 0; } }
+  flowCount.fill(0);
+}