Check if a double is NaN before converting to it int (#61940)

packages/flutter/lib/src/painting/matrix_utils.dart

@@ -127,6 +127,13 @@ class MatrixUtils {
   ///
   /// This function assumes the given point has a z-coordinate of 0.0. The
   /// z-coordinate of the result is ignored.
+  ///
+  /// While not common, this method may return (NaN, NaN), iff the given `point`
+  /// results in a "point at infinity" in homogeneous coordinates after applying
+  /// the `transform`. For example, a [RenderObject] may set its transform to
+  /// the zero matrix to indicate its content is currently not visible. Trying
+  /// to convert an `Offset` to its coordinate space always results in
+  /// (NaN, NaN).
   static Offset transformPoint(Matrix4 transform, Offset point) {
     final Float64List storage = transform.storage;
     final double x = point.dx;

packages/flutter/lib/src/rendering/box.dart

@@ -2293,7 +2293,9 @@ abstract class RenderBox extends RenderObject {
   /// coordinate system of `ancestor` (which must be an ancestor of this render
   /// object) instead of to the global coordinate system.
   ///
-  /// This method is implemented in terms of [getTransformTo].
+  /// This method is implemented in terms of [getTransformTo]. If the transform
+  /// matrix puts the given `point` on the line at infinity (for instance, when
+  /// the transform matrix is the zero matrix), this method returns (NaN, NaN).
   Offset localToGlobal(Offset point, { RenderObject ancestor }) {
     return MatrixUtils.transformPoint(getTransformTo(ancestor), point);
   }

packages/flutter/lib/src/rendering/editable.dart

@@ -1936,10 +1936,12 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin {
   Offset _getPixelPerfectCursorOffset(Rect caretRect) {
     final Offset caretPosition = localToGlobal(caretRect.topLeft);
     final double pixelMultiple = 1.0 / _devicePixelRatio;
-    final int quotientX = (caretPosition.dx / pixelMultiple).round();
-    final int quotientY = (caretPosition.dy / pixelMultiple).round();
-    final double pixelPerfectOffsetX = quotientX * pixelMultiple - caretPosition.dx;
-    final double pixelPerfectOffsetY = quotientY * pixelMultiple - caretPosition.dy;
+    final double pixelPerfectOffsetX = caretPosition.dx.isFinite
+      ? (caretPosition.dx / pixelMultiple).round() * pixelMultiple - caretPosition.dx
+      : caretPosition.dx;
+    final double pixelPerfectOffsetY = caretPosition.dy.isFinite
+      ? (caretPosition.dy / pixelMultiple).round() * pixelMultiple - caretPosition.dy
+      : caretPosition.dy;
     return Offset(pixelPerfectOffsetX, pixelPerfectOffsetY);
   }
 

packages/flutter/test/widgets/editable_text_test.dart

@@ -4321,6 +4321,30 @@ void main() {
     expect(scrollController.offset, 0);
   });
 
+  testWidgets('getLocalRectForCaret does not throw when it sees an infinite point', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: SkipPainting(
+          child: Transform(
+            transform: Matrix4.zero(),
+            child: EditableText(
+              controller: TextEditingController(),
+              focusNode: FocusNode(),
+              style: textStyle,
+              cursorColor: Colors.blue,
+              backgroundCursorColor: Colors.grey,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+    final Rect rect = state.renderEditable.getLocalRectForCaret(const TextPosition(offset: 0));
+    expect(rect.isFinite, false);
+    expect(tester.takeException(), isNull);
+  });
+
   testWidgets('obscured multiline fields throw an exception', (WidgetTester tester) async {
     final TextEditingController controller = TextEditingController();
     expect(
@@ -5350,3 +5374,15 @@ class NoImplicitScrollPhysics extends AlwaysScrollableScrollPhysics {
     return NoImplicitScrollPhysics(parent: buildParent(ancestor));
   }
 }
+
+class SkipPainting extends SingleChildRenderObjectWidget {
+  const SkipPainting({ Key key, Widget child }): super(key: key, child: child);
+
+  @override
+  SkipPaintingRenderObject createRenderObject(BuildContext context) => SkipPaintingRenderObject();
+}
+
+class SkipPaintingRenderObject extends RenderProxyBox {
+  @override
+  void paint(PaintingContext context, Offset offset) { }
+}