fix: fix triangulate

CHANGELOG.md

@@ -38,6 +38,11 @@ So your change should look like:
 
 ## [unreleased]
 
+### Breaking Changes
+
+- `triangulate()` now returns a flat list of the new indices, instead of a list
+  of 3-tuples of points (#1103) - @dragoncoder047
+
 ### Added
 
 - Made random generator algorithm configurable using `setRNG()` (#1057) -
@@ -59,6 +64,8 @@ So your change should look like:
 
 ### Fixed
 
+- Fixed `triangulate()` returning invalid triangles in some cases (#1093) -
+  @dragoncoder047
 - Fixed `TimerController.timeLeft` returning elapsed time instead of remaining
   time (#1082) - @nojaf
 - Fixed mouse coordinates not being calculated properly when canvas is resized
@@ -523,10 +530,12 @@ So your change should look like:
 
 - Now, you can use `color(c)` with a hexadecimal literal number (ex: 0x00ff00) -
   @lajbel
+
   ```js
   // blue frog
   add([sprite("bean"), color(0x0000ff)]);
   ```
+
 - **(!)** `KAPLAYCtx` doesn't use generics anymore. Now, `KAPLAYCtxT` uses
   them - @lajbel
 - Now, `kaplay` will return `KAPLAYCtx` or `KAPLAYCtxT` depending if it's using

examples/polygon.js

@@ -49,12 +49,12 @@ let dragging = null;
 let hovering = null;
 
 poly.onDraw(() => {
-    const triangles = triangulate(poly.pts);
-    for (const triangle of triangles) {
+    const triangleIndices = triangulate(poly.pts);
+    for (let i = 0; i < triangleIndices.length; i += 3) {
         drawTriangle({
-            p1: triangle[0],
-            p2: triangle[1],
-            p3: triangle[2],
+            p1: poly.pts[triangleIndices[i]],
+            p2: poly.pts[triangleIndices[i + 1]],
+            p3: poly.pts[triangleIndices[i + 2]],
             fill: false,
             outline: { color: BLACK },
         });

src/core/contextType.ts

@@ -6432,8 +6432,9 @@ export interface KAPLAYCtx {
      * @since v3001.0
      * @group Math
      * @subgroup Advanced
+     * @returns flattened list of indices of each of the decomposed triangles, list will always have a multiple of 3 length
      */
-    triangulate(pts: Vec2[]): Vec2[][];
+    triangulate(pts: Vec2[]): number[];
     /**
      * @returns the convex hull of the given polygon.
      * @since v4000.0

src/gfx/draw/drawPolygon.ts

@@ -156,10 +156,7 @@ export function drawPolygon(opt: DrawPolygonOpt) {
         let indices;
 
         if (opt.triangulate /* && !isConvex(opt.pts)*/) {
-            const triangles = triangulate(opt.pts);
-            // TODO rewrite triangulate to just return new indices
-            indices = triangles.map(t => t.map(p => opt.pts.indexOf(p)))
-                .flat();
+            indices = triangulate(opt.pts);
         }
         else {
             indices = [...Array(npts - 2).keys()]

src/math/math.ts

@@ -3257,7 +3257,8 @@ function pointInTriangle(p: Vec2, a: Vec2, b: Vec2, c: Vec2) {
 
 // true if any vertex in the list `vertices' is in the triangle abc.
 function someInTriangle(vertices: Vec2[], a: Vec2, b: Vec2, c: Vec2) {
-    for (const p of vertices) {
+    for (let i = 0; i < vertices.length; i++) {
+        const p = vertices[i]!;
         if (
             (p !== a) && (p !== b) && (p !== c) && pointInTriangle(p, a, b, c)
         ) {
@@ -3273,41 +3274,24 @@ function isEar(a: Vec2, b: Vec2, c: Vec2, vertices: Vec2[]) {
     return isOrientedCcw(a, b, c) && !someInTriangle(vertices, a, b, c);
 }
 
-export function triangulate(pts: Vec2[]): Vec2[][] {
-    if (pts.length < 3) {
-        return [];
-    }
-    if (pts.length == 3) {
-        return [pts];
+export function triangulate(pts: Vec2[]): number[] {
+    const len = pts.length;
+
+    if (len < 3) return [];
+    if (len === 3) {
+        return [0, 1, 2];
     }
 
     /* Create a list of indexes to the previous and next points of a given point
     prev_idx[i] gives the index to the previous point of the point at i */
-    let nextIdx = [];
-    let prevIdx = [];
-    let idx = 0;
-    for (let i = 0; i < pts.length; i++) {
-        const lm = pts[idx];
-        const pt = pts[i];
-        if (pt.x < lm.x || (pt.x == lm.x && pt.y < lm.y)) {
-            idx = i;
-        }
-        nextIdx[i] = i + 1;
-        prevIdx[i] = i - 1;
-    }
-    nextIdx[nextIdx.length - 1] = 0;
-    prevIdx[0] = prevIdx.length - 1;
+    let prevIdx = pts.map((_, i) => (i + len - 1) % len);
+    let nextIdx = pts.map((_, i) => (i + 1) % len);
 
     // If the polygon is not counter clockwise, swap the lists, thus reversing the winding
     if (!isOrientedCcwPolygon(pts)) {
-        [nextIdx, prevIdx] = [prevIdx, nextIdx];
-    }
-
-    const concaveVertices = [];
-    for (let i = 0; i < pts.length; ++i) {
-        if (!isOrientedCcw(pts[prevIdx[i]], pts[i], pts[nextIdx[i]])) {
-            concaveVertices.push(pts[i]);
-        }
+        let temp = prevIdx;
+        prevIdx = nextIdx;
+        nextIdx = temp;
     }
 
     const triangles = [];
@@ -3322,11 +3306,10 @@ export function triangulate(pts: Vec2[]): Vec2[][] {
         const a = pts[prev];
         const b = pts[current];
         const c = pts[next];
-        if (isEar(a, b, c, concaveVertices)) {
-            triangles.push([a, b, c]);
+        if (isEar(a, b, c, pts)) {
+            triangles.push(prev, current, next);
             nextIdx[prev] = next;
             prevIdx[next] = prev;
-            concaveVertices.splice(concaveVertices.indexOf(b), 1);
             --nVertices;
             skipped = 0;
         }
@@ -3337,7 +3320,7 @@ export function triangulate(pts: Vec2[]): Vec2[][] {
     }
     next = nextIdx[current];
     prev = prevIdx[current];
-    triangles.push([pts[prev], pts[current], pts[next]]);
+    triangles.push(prev, current, next);
 
     return triangles;
 }

tests/playtests/hyperconcave_polygon.js

@@ -0,0 +1,103 @@
+kaplay({
+    background: [0, 0, 0],
+});
+
+add([
+    text("Drag corners of the polygon"),
+    pos(20, 20),
+]);
+
+// Make a weird shape
+const poly = add([
+    polygon([
+        vec2(0, 0),
+        vec2(100, 0),
+        vec2(200, 100),
+        vec2(100, 200),
+        vec2(0, 100),
+        vec2(80, 100),
+    ], {
+        colors: [
+            rgb(128, 255, 128),
+            rgb(255, 128, 128),
+            rgb(128, 128, 255),
+            rgb(255, 128, 128),
+            rgb(128, 128, 128),
+            rgb(128, 255, 128),
+        ],
+        triangulate: true,
+    }),
+    pos(150, 150),
+    area(),
+    color(),
+]);
+
+let dragging = null;
+let hovering = null;
+
+poly.onDraw(() => {
+    const triangleIndices = triangulate(poly.pts);
+    for (var i = 0; i < triangleIndices.length; i += 3) {
+        drawTriangle({
+            p1: poly.pts[triangleIndices[i]],
+            p2: poly.pts[triangleIndices[i + 1]],
+            p3: poly.pts[triangleIndices[i + 2]],
+            fill: false,
+            outline: { color: BLACK },
+        });
+    }
+    if (hovering !== null) {
+        drawCircle({
+            pos: poly.pts[hovering],
+            radius: 16,
+        });
+    }
+});
+
+onUpdate(() => {
+    if (isConvex(poly.pts)) {
+        poly.color = WHITE;
+    }
+    else {
+        poly.color = rgb(192, 192, 192);
+    }
+});
+
+onMousePress(() => {
+    dragging = hovering;
+});
+
+onMouseRelease(() => {
+    dragging = null;
+});
+
+onMouseMove(() => {
+    hovering = null;
+    const mp = mousePos().sub(poly.pos);
+    for (let i = 0; i < poly.pts.length; i++) {
+        if (mp.dist(poly.pts[i]) < 16) {
+            hovering = i;
+            break;
+        }
+    }
+    if (dragging !== null) {
+        poly.pts[dragging] = mousePos().sub(poly.pos);
+    }
+});
+
+poly.onHover(() => {
+    poly.color = rgb(200, 200, 255);
+});
+
+poly.onHoverEnd(() => {
+    poly.color = rgb(255, 255, 255);
+});
+
+poly.onDraw(() => {
+    drawPolygon({
+        ...poly,
+        pos: vec2(),
+        fill: false,
+        outline: { color: RED, width: 5 },
+    });
+});