refactor(grid-iterators): update clipped shape iters

- better pre-clipping for circle/line
- intern intersection/clipping helpers

packages/grid-iterators/package.json

@@ -81,8 +81,8 @@
         "./circle": {
             "import": "./circle.js"
         },
-        "./clipped": {
-            "import": "./clipped.js"
+        "./clipping": {
+            "import": "./clipping.js"
         },
         "./column-ends": {
             "import": "./column-ends.js"

packages/grid-iterators/src/circle.ts

@@ -1,6 +1,6 @@
-import { clipped } from "./clipped.js";
+import { asInt } from "@thi.ng/api/typedarray";
+import { clipped, intersectRectCircle } from "./clipping.js";
 import { hline } from "./hvline.js";
-import { asInt } from "./utils.js";
 
 export function* circle(cx: number, cy: number, r: number, fill = true) {
     [cx, cy, r] = asInt(cx, cy, r);
@@ -49,7 +49,8 @@ export function* circle(cx: number, cy: number, r: number, fill = true) {
 
 /**
  * Version of {@link circle} yielding only coordinates in rect defined by
- * `left,top`..`right,bottom`.
+ * `left,top`..`right,bottom`. Returns undefined if circle lies completely
+ * outside given clip rectangle.
  *
  * @param cx
  * @param cy
@@ -69,4 +70,8 @@ export const circleClipped = (
     right: number,
     bottom: number,
     fill = true
-) => clipped(circle(cx, cy, r, fill), left, top, right, bottom);
+) => {
+    return intersectRectCircle(left, top, right, bottom, cx, cy, r)
+        ? clipped(circle(cx, cy, r, fill), left, top, right, bottom)
+        : undefined;
+};

packages/grid-iterators/src/clipping.ts

@@ -0,0 +1,101 @@
+import type { FnN3, FnU2, FnU7, FnU8, Tuple } from "@thi.ng/api";
+
+/**
+ * Filters points from `src` iterable to remove any falling outside the rect
+ * defined by `left,top`..`right,bottom`.
+ *
+ * @param src
+ * @param left
+ * @param top
+ * @param right
+ * @param bottom
+ */
+export function* clipped(
+    src: Iterable<number[]>,
+    left: number,
+    top: number,
+    right: number,
+    bottom: number
+) {
+    for (let p of src) {
+        if (p[0] >= left && p[0] < right && p[1] >= top && p[1] < bottom)
+            yield p;
+    }
+}
+
+/** @internal */
+const axis: FnN3 = (a, b, c) =>
+    (a < b ? a - b : a > b + c ? a - b - c : 0) ** 2;
+
+/**
+ * Based on {@link @thi.ng/geom-isec}, but inlined to avoid dependency.
+ *
+ * @param x
+ * @param y
+ * @param w
+ * @param h
+ * @param cx
+ * @param cy
+ * @param r
+ *
+ * @internal
+ */
+export const intersectRectCircle: FnU7<number, boolean> = (
+    x,
+    y,
+    w,
+    h,
+    cx,
+    cy,
+    r
+) => axis(cx, x, w) + axis(cy, y, h) <= r * r;
+
+/**
+ * Based on {@link @thi.ng/geom-clip-line#liangBarsky2Raw}, but with diff return type.
+ *
+ * @param ax
+ * @param ay
+ * @param bx
+ * @param by
+ * @param minx
+ * @param miny
+ * @param maxx
+ * @param maxy
+ *
+ * @internal
+ */
+export const liangBarsky: FnU8<number, Tuple<number, 4> | undefined> = (
+    ax,
+    ay,
+    bx,
+    by,
+    minx,
+    miny,
+    maxx,
+    maxy
+) => {
+    const dx = bx - ax;
+    const dy = by - ay;
+    let alpha = 0;
+    let beta = 1;
+    const clip: FnU2<number, boolean> = (p, q) => {
+        if (p < 0) {
+            const r = q / p;
+            if (r > beta) return false;
+            r > alpha && (alpha = r);
+        } else if (p > 0) {
+            const r = q / p;
+            if (r < alpha) return false;
+            r < beta && (beta = r);
+        } else if (q < 0) {
+            return false;
+        }
+        return true;
+    };
+    return clip(-dx, ax - minx) &&
+        clip(dx, maxx - ax) &&
+        clip(-dy, ay - miny) &&
+        clip(dy, maxy - ay)
+        ? [alpha * dx + ax, alpha * dy + ay, beta * dx + ax, beta * dy + ay]
+        : undefined;
+};

packages/grid-iterators/src/index.ts

@@ -1,5 +1,5 @@
 export * from "./circle.js";
-export * from "./clipped.js";
+export * from "./clipping.js";
 export * from "./column-ends.js";
 export * from "./columns.js";
 export * from "./diagonal.js";

packages/grid-iterators/src/line.ts

@@ -1,5 +1,5 @@
-import { clipped } from "./clipped.js";
-import { asInt } from "./utils.js";
+import { asInt } from "@thi.ng/api/typedarray";
+import { liangBarsky } from "./clipping";
 
 export function* line(ax: number, ay: number, bx: number, by: number) {
     [ax, ay, bx, by] = asInt(ax, ay, bx, by);
@@ -26,7 +26,8 @@ export function* line(ax: number, ay: number, bx: number, by: number) {
 
 /**
  * Version of {@link line} yielding only coordinates in rect defined by
- * `left,top`..`right,bottom`.
+ * `left,top`..`right,bottom`. Returns undefined if circle lies completely
+ * outside given clip rectangle.
  *
  * @param x1
  * @param y1
@@ -46,4 +47,7 @@ export const lineClipped = (
     top: number,
     right: number,
     bottom: number
-) => clipped(line(x1, y1, x2, y2), left, top, right, bottom);
+) => {
+    const res = liangBarsky(x1, y1, x2, y2, left, top, right, bottom);
+    return res ? line(res[0], res[1], res[2], res[3]) : undefined;
+};