Moves all argument checking of Vertices() and Vertices.raw() to asserts, Adds arg checking to all web renderers -Fixes #123085

lib/ui/painting.dart

@@ -4714,8 +4714,10 @@ class Vertices extends NativeFieldWrapperClass1 {
       throw ArgumentError('"positions" and "textureCoordinates" lengths must match.');
     }
     if (indices != null) {
+      final int halfPositions = positions.length >> 1;  // len/2 - we already checked that positions.length is even
       for (int index = 0; index < indices.length; index += 1) {
-        if (indices[index] * 2 >= positions.length) {
+        // we need to check that `indices[index] * 2 >= positions.length`, so do it without multiplying
+        if (indices[index] >= halfPositions) {
           throw ArgumentError(
             '"indices" values must be valid indices in the positions list '
             '(i.e. numbers in the range 0..${positions.length ~/ 2 - 1}), '

lib/web_ui/lib/src/engine/canvaskit/vertices.dart

@@ -47,6 +47,9 @@ class CkVertices implements ui.Vertices {
     Int32List? colors,
     Uint16List? indices,
   }) {
+    if (positions.length % 2 != 0) {
+      throw ArgumentError('"positions" must have an even number of entries (each coordinate is an x,y pair).');
+    }
     if (textureCoordinates != null &&
         textureCoordinates.length != positions.length) {
       throw ArgumentError(
@@ -55,8 +58,11 @@ class CkVertices implements ui.Vertices {
     if (colors != null && colors.length * 2 != positions.length) {
       throw ArgumentError('"positions" and "colors" lengths must match.');
     }
+    // see ui.Vertices.raw() - all indices must be <(positions.length/2) because they refer to
+    // pairs in the positions array.
+    final int halfPositions = positions.length >> 1;
     if (indices != null &&
-        indices.any((int i) => i < 0 || i >= positions.length)) {
+        indices.any((int i) => i < 0 || i >= halfPositions)) {
       throw ArgumentError(
           '"indices" values must be valid indices in the positions list.');
     }

lib/web_ui/test/canvaskit/vertices_test.dart

@@ -66,6 +66,60 @@ void testMain() {
         .draw(builder.build().layerTree);
     await matchGoldenFile('canvaskit_vertices_antialiased.png', region: region);
   }, skip: isSafari);
+
+  test('Vertices checks', () {
+    try {
+      ui.Vertices(
+        ui.VertexMode.triangles,
+        const <ui.Offset>[ui.Offset.zero, ui.Offset.zero, ui.Offset.zero],
+        indices: Uint16List.fromList(const <int>[0, 2, 5]),
+      );
+      throw ArgumentError('Vertices did not throw the expected error.');
+    } on ArgumentError catch (e) {
+      expect('$e', 'Invalid argument(s): "indices" values must be valid indices in the positions list.');
+    }
+    ui.Vertices( // This one does not throw.
+      ui.VertexMode.triangles,
+      const <ui.Offset>[ui.Offset.zero],
+    ).dispose();
+    ui.Vertices( // This one should not throw.
+      ui.VertexMode.triangles,
+      const <ui.Offset>[ui.Offset.zero, ui.Offset.zero, ui.Offset.zero],
+      indices: Uint16List.fromList(const <int>[0, 2, 1, 2, 0, 1, 2, 0]), // Uint16List implements List<int> so this is ok.
+    ).dispose();
+  });
+
+  test('Vertices.raw checks', () {
+    try {
+      ui.Vertices.raw(
+        ui.VertexMode.triangles,
+        Float32List.fromList(const <double>[0.0]),
+      );
+      throw ArgumentError('Vertices.raw did not throw the expected error.');
+    } on ArgumentError catch (e) {
+      expect('$e', 'Invalid argument(s): "positions" must have an even number of entries (each coordinate is an x,y pair).');
+    }
+    try {
+      ui.Vertices.raw(
+        ui.VertexMode.triangles,
+        Float32List.fromList(const <double>[0.0, 0.0, 0.0, 0.0, 0.0, 0.0]),
+        indices: Uint16List.fromList(const <int>[0, 2, 5]),
+      );
+      throw ArgumentError('Vertices.raw did not throw the expected error.');
+    } on ArgumentError catch (e) {
+      expect('$e', 'Invalid argument(s): "indices" values must be valid indices in the positions list.');
+    }
+    ui.Vertices.raw( // This one does not throw.
+      ui.VertexMode.triangles,
+      Float32List.fromList(const <double>[0.0, 0.0]),
+    ).dispose();
+    ui.Vertices.raw( // This one should not throw.
+      ui.VertexMode.triangles,
+      Float32List.fromList(const <double>[0.0, 0.0, 0.0, 0.0, 0.0, 0.0]),
+      indices: Uint16List.fromList(const <int>[0, 2, 1, 2, 0, 1, 2, 0]),
+    ).dispose();
+  });
+
 }
 
 CkVertices _testVertices() {