fix: Keep one non-finite value from corrupting its compressed PLY chunk

src/lib/writers/compressed-chunk.ts

@@ -53,20 +53,23 @@ class CompressedChunk {
     }
 
     pack() {
+        // Bounds over the finite values only: a single NaN/Infinity would otherwise
+        // make the whole chunk's bounds non-finite and corrupt all 256 splats.
         const calcMinMax = (data: Float32Array) => {
-            let min;
-            let max;
-            min = max = data[0];
-            for (let i = 1; i < data.length; ++i) {
+            let min = Infinity;
+            let max = -Infinity;
+            for (let i = 0; i < data.length; ++i) {
                 const v = data[i];
-                min = Math.min(min, v);
-                max = Math.max(max, v);
+                if (Number.isFinite(v)) {
+                    if (v < min) min = v;
+                    if (v > max) max = v;
+                }
             }
-            return { min, max };
+            return min <= max ? { min, max } : { min: 0, max: 0 };
         };
 
         const normalize = (x: number, min: number, max: number) => {
-            if (x <= min) return 0;
+            if (Number.isNaN(x) || x <= min) return 0;
             if (x >= max) return 1;
             return max - min < 0.00001 ? 0 : (x - min) / (max - min);
         };

test/formats.test.mjs

@@ -270,6 +270,28 @@ describe('Compressed PLY Format', () => {
         compareSummaries(actualSummary, expectedSummary, { tolerance: 0.1 });
     });
 
+    it('a non-finite value must not corrupt the rest of its 256-splat chunk', async () => {
+        const dt = createTestDataTable(256);
+        dt.transform = Transform.PLY.clone();
+        dt.getColumnByName('x').data[7] = NaN;
+        dt.getColumnByName('scale_0').data[9] = NaN;
+        dt.getColumnByName('f_dc_1').data[11] = NaN;
+
+        const writeFs = new MemoryFileSystem();
+        await writeCompressedPly({ filename: 'nan.compressed.ply', dataTable: dt }, writeFs);
+
+        const pool = createChunkDataPool();
+        const readBack = await materializeToDataTable(
+            await readPly(new BufferReadSource(writeFs.results.get('nan.compressed.ply')), pool), pool
+        );
+
+        // Before the fix all 256 splats decoded as NaN in each of these columns.
+        for (const name of ['x', 'scale_0', 'f_dc_1']) {
+            const nanCount = Array.from(readBack.getColumnByName(name).data).filter(Number.isNaN).length;
+            assert.strictEqual(nanCount, 0, `${name}: ${nanCount} NaN values after round-trip`);
+        }
+    });
+
     it('writeCompressedPlySource (ChunkSource adapter) == writeCompressedPly byte-for-byte', async () => {
         const dt = createTestDataTable(300, { includeSH: true, shBands: 1 });
         dt.transform = Transform.PLY.clone();