Add fuzz test for BrushTipShape constructor

To make sure that it doesn't crash even if the tip modeler sends it large, infinite, or in some cases even NaN tip state parameters.

PiperOrigin-RevId: 831487601

Author: Ink Open Source

ink/strokes/internal/BUILD.bazel

@@ -19,6 +19,19 @@ package(
     default_visibility = ["//ink:__subpackages__"],
 )
 
+cc_library(
+    name = "fuzz_domains",
+    testonly = 1,
+    srcs = ["fuzz_domains.cc"],
+    hdrs = ["fuzz_domains.h"],
+    deps = [
+        ":brush_tip_state",
+        "//ink/geometry:angle",
+        "//ink/geometry:fuzz_domains",
+        "@com_google_fuzztest//fuzztest",
+    ],
+)
+
 cc_library(
     name = "mutable_multi_mesh",
     srcs = ["mutable_multi_mesh.cc"],
@@ -365,12 +378,14 @@ cc_test(
         ":brush_tip_shape",
         ":brush_tip_state",
         ":extrusion_points",
+        ":fuzz_domains",
         "//ink/geometry:angle",
         "//ink/geometry:type_matchers",
         "//ink/geometry/internal:circle",
         "//ink/geometry/internal:test_matchers",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:span",
+        "@com_google_fuzztest//fuzztest",
         "@com_google_googletest//:gtest_main",
     ],
 )

ink/strokes/internal/brush_tip_shape_test.cc

@@ -18,6 +18,7 @@
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include "fuzztest/fuzztest.h"
 #include "absl/strings/str_cat.h"
 #include "absl/types/span.h"
 #include "ink/geometry/angle.h"
@@ -26,6 +27,7 @@
 #include "ink/geometry/type_matchers.h"
 #include "ink/strokes/internal/brush_tip_state.h"
 #include "ink/strokes/internal/extrusion_points.h"
+#include "ink/strokes/internal/fuzz_domains.h"
 
 namespace ink::strokes_internal {
 namespace {
@@ -1477,5 +1479,13 @@ TEST(BrushTipShapeTest, ContainsWithRoundedTriangleEdgeCase) {
   EXPECT_FALSE(rounded_triangle.Contains(circle));
 }
 
+void CanConstructFromAnyValidTipState(const BrushTipState& tip_state,
+                                      float min_nonzero_radius_and_separation) {
+  BrushTipShape tip_shape(tip_state, min_nonzero_radius_and_separation);
+  EXPECT_THAT(tip_shape.Center(), NanSensitivePointEq(tip_state.position));
+}
+FUZZ_TEST(BrushTipShapeTest, CanConstructFromAnyValidTipState)
+    .WithDomains(ValidBrushTipState(), fuzztest::NonNegative<float>());
+
 }  // namespace
 }  // namespace ink::strokes_internal

ink/strokes/internal/fuzz_domains.cc

@@ -0,0 +1,40 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "ink/strokes/internal/fuzz_domains.h"
+
+#include "fuzztest/fuzztest.h"
+#include "ink/geometry/angle.h"
+#include "ink/geometry/fuzz_domains.h"
+#include "ink/strokes/internal/brush_tip_state.h"
+
+namespace ink::strokes_internal {
+
+fuzztest::Domain<BrushTipState> ValidBrushTipState() {
+  return fuzztest::StructOf<BrushTipState>(
+      /*position=*/ArbitraryPoint(),
+      /*width=*/fuzztest::NonNegative<float>(),
+      /*height=*/fuzztest::NonNegative<float>(),
+      /*percent_radius=*/fuzztest::InRange<float>(0, 1),
+      /*rotation=*/NormalizedAngle(),
+      /*slant=*/AngleInRange(-kHalfTurn, kHalfTurn),
+      /*pinch=*/fuzztest::InRange<float>(0, 1),
+      /*texture_animation_progress_offset=*/fuzztest::InRange<float>(0, 1),
+      /*hue_offset_in_full_turns=*/fuzztest::InRange<float>(0, 1),
+      /*saturation_multiplier=*/fuzztest::InRange<float>(0, 2),
+      /*luminosity_shift=*/fuzztest::InRange<float>(-1, 1),
+      /*opacity_multiplier=*/fuzztest::InRange<float>(0, 2));
+}
+
+}  // namespace ink::strokes_internal

ink/strokes/internal/fuzz_domains.h

@@ -0,0 +1,27 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef INK_STROKES_INTERNAL_FUZZ_DOMAINS_H_
+#define INK_STROKES_INTERNAL_FUZZ_DOMAINS_H_
+
+#include "fuzztest/fuzztest.h"
+#include "ink/strokes/internal/brush_tip_state.h"
+
+namespace ink::strokes_internal {
+
+fuzztest::Domain<BrushTipState> ValidBrushTipState();
+
+}  // namespace ink::strokes_internal
+
+#endif  // INK_STROKES_INTERNAL_FUZZ_DOMAINS_H_