Shadow cast algorithm

src/common/navigation/bresenham.ts

@@ -1,4 +1,5 @@
 import { clamp } from "@common/utils";
+import { shadowCast } from "./fov";
 
 interface Point {
     x: number;
@@ -21,7 +22,7 @@ interface BresenhamOptions {
 
 export interface BresenhamLineOptions extends BresenhamOptions { }
 
-interface BresenhamCircleBaseOptions<T extends boolean | 'fov'> extends BresenhamOptions {
+interface BresenhamCircleBaseOptions<T extends boolean | 'fov' | 'shadow'> extends BresenhamOptions {
     /**
      * - `false` (default) — outline only.
      * - `true` — filled disc (span-from-outline scanline).
@@ -31,7 +32,7 @@ interface BresenhamCircleBaseOptions<T extends boolean | 'fov'> extends Bresenha
 }
 
 type BresenhamCircleFillOptions = BresenhamCircleBaseOptions<boolean>;
-interface BresenhamCircleFovOptions extends BresenhamCircleBaseOptions<'fov'> {
+interface BresenhamCircleFovOptions extends BresenhamCircleBaseOptions<'fov' | 'shadow'> {
     /** 
      * A callback that is called for each point on the ray casted from the start
      * point to the current point. If the callback returns `true`, the ray is
@@ -323,6 +324,14 @@ export function* bresenhamCircleGen(
         return;
     }
 
+    if (options?.fill === 'shadow') {
+        yield* shadowCast(x, y, r, (x, y) => {
+            if (!inBounds(x, y)) return true;
+            return options?.breaker?.(x, y) ?? false;
+        });
+        return;
+    }
+
     if (fill) {
         // Span-from-outline: use the midpoint algorithm to find the exact
         // horizontal extent for each row, then fill between those extents.

src/common/navigation/fov.ts

@@ -0,0 +1,102 @@
+export function* shadowCast(
+    x: number,
+    y: number,
+    r: number,
+    breaker: (x: number, y: number) => boolean
+): Generator<{ x: number; y: number }> {
+    if (r < 0) return;
+
+    const radiusSq = r * r;
+    const seen = new Set<string>();
+    const keyOf = (px: number, py: number) => `${px},${py}`;
+
+    // Yield the source tile itself if it is not blocked.
+    if (!breaker(x, y)) {
+        seen.add(keyOf(x, y));
+        yield { x, y };
+    }
+
+    type Frame = {
+        octant: number;
+        row: number;
+        start: number;
+        end: number;
+    };
+
+    // 8 octants around the origin.
+    const OCTANTS: ReadonlyArray<readonly [number, number, number, number]> = [
+        [1, 0, 0, 1],
+        [0, 1, 1, 0],
+        [0, 1, -1, 0],
+        [1, 0, 0, -1],
+        [-1, 0, 0, -1],
+        [0, -1, -1, 0],
+        [0, -1, 1, 0],
+        [-1, 0, 0, 1],
+    ];
+
+    const stack: Frame[] = [];
+    for (let octant = 7; octant >= 0; octant--) {
+        stack.push({ octant, row: 1, start: 1.0, end: 0.0 });
+    }
+
+    while (stack.length > 0) {
+        const frame = stack.pop()!;
+        if (frame.start < frame.end) continue;
+
+        const [xx, xy, yx, yy] = OCTANTS[frame.octant];
+
+        let start = frame.start;
+        let blocked = false;
+        let newStart = start;
+
+        for (let row = frame.row; row <= r; row++) {
+            let dx = -row - 1;
+            const dy = -row;
+
+            while (dx <= 0) {
+                dx++;
+
+                const mapX = x + dx * xx + dy * xy;
+                const mapY = y + dx * yx + dy * yy;
+
+                const leftSlope = (dx - 0.5) / (dy + 0.5);
+                const rightSlope = (dx + 0.5) / (dy - 0.5);
+
+                if (start < rightSlope) continue;
+                if (frame.end > leftSlope) break;
+
+                const opaque = breaker(mapX, mapY);
+
+                if (dx * dx + dy * dy <= radiusSq && !opaque) {
+                    const key = keyOf(mapX, mapY);
+                    if (!seen.has(key)) {
+                        seen.add(key);
+                        yield { x: mapX, y: mapY };
+                    }
+                }
+
+                if (blocked) {
+                    if (opaque) {
+                        newStart = rightSlope;
+                        continue;
+                    }
+
+                    blocked = false;
+                    start = newStart;
+                } else if (opaque && row < r) {
+                    blocked = true;
+                    stack.push({
+                        octant: frame.octant,
+                        row: row + 1,
+                        start,
+                        end: leftSlope,
+                    });
+                    newStart = rightSlope;
+                }
+            }
+
+            if (blocked) break;
+        }
+    }
+}

src/games/dropballs/index.ts

@@ -1,6 +1,6 @@
 import { createCanvas } from "@common/display/canvas";
 import { gameLoop } from "@common/game";
-import { bresenhamCircleGen } from "@common/navigation/bresenham";
+import { circleGen } from "@common/navigation/bresenham";
 import Physics from "@common/physics";
 import { mapNumber } from "@common/utils";
 
@@ -162,7 +162,7 @@ const frame = (dt: number, state: State) => {
 
 function fillCircle(ctx: CanvasRenderingContext2D, xc: number, yc: number, r: number) {
     // because default circle fill is antialiased
-    for (const { x, y } of bresenhamCircleGen(xc, yc, r, { fill: true })) {
+    for (const { x, y } of circleGen(xc, yc, r, { fill: true })) {
         ctx.fillRect(x, y, 1, 1);
     }
 }

src/games/playground/index.tsx

@@ -3,6 +3,8 @@ import { bresenhamCircleGen } from "@common/navigation/bresenham";
 
 const S = 20;
 
+const breaker = (x: number, y: number) => Math.hypot(x - S * 0.3, y - S * 0.3) <= S / 16;
+
 export default async function main() {
     const canvas = createCanvas(S, S);
 
@@ -10,12 +12,11 @@ export default async function main() {
     if (!ctx) return;
 
     ctx.fillStyle = 'black';
-    for (const fill of [true, false, 'fov'] as const) {
+    for (const fill of ['fov', 'shadow'] as const) {
         let i = 0;
 
         console.time(`fill=${fill}`);
-        // @ts-ignore
-        for (const { x, y } of bresenhamCircleGen(S / 2, S / 2, S * 0.4, { fill })) {
+        for (const { x, y } of bresenhamCircleGen(S / 2, S / 2, S * 0.4, { fill, breaker })) {
             i++;
             ctx.fillRect(x, y, 1, 1);
         }