[Impeller] null check samplers (flutter#37489)

* [Impeller] null check sampler and assert in Paint

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* Update fragment_shader_test.dart

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* TESTING

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* TESTING

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* remove debugging code

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Author: Jonah Williams

display_list/display_list_color_source.h

@@ -705,7 +705,11 @@ class DlRuntimeEffectColorSource final : public DlColorSource {
     }
     std::vector<sk_sp<SkShader>> sk_samplers(samplers_.size());
     for (size_t i = 0; i < samplers_.size(); i++) {
-      sk_samplers[i] = samplers_[i]->skia_object();
+      auto sampler = samplers_[i];
+      if (sampler == nullptr) {
+        return nullptr;
+      }
+      sk_samplers[i] = sampler->skia_object();
     }
 
     auto ref = new std::shared_ptr<std::vector<uint8_t>>(uniform_data_);

display_list/display_list_color_source_unittests.cc

@@ -974,5 +974,14 @@ TEST(DisplayListColorSource, RuntimeEffect) {
   TestNotEquals(source2, source3, "SkRuntimeEffect differs");
 }
 
+TEST(DisplayListColorSource, RuntimeEffectWithNullSampler) {
+  std::shared_ptr<DlRuntimeEffectColorSource> source1 =
+      DlColorSource::MakeRuntimeEffect(
+          kTestRuntimeEffect1, {nullptr},
+          std::make_shared<std::vector<uint8_t>>());
+
+  ASSERT_EQ(source1->skia_object(), nullptr);
+}
+
 }  // namespace testing
 }  // namespace flutter

impeller/display_list/display_list_dispatcher.cc

@@ -442,6 +442,9 @@ void DisplayListDispatcher::setColorSource(
       std::vector<RuntimeEffectContents::TextureInput> texture_inputs;
 
       for (auto& sampler : samplers) {
+        if (sampler == nullptr) {
+          return;
+        }
         auto* image = sampler->asImage();
         if (!sampler->asImage()) {
           UNIMPLEMENTED;

lib/ui/dart_ui.cc

@@ -175,6 +175,7 @@ typedef CanvasPath Path;
   V(FragmentProgram, initFromAsset, 2)                 \
   V(ReusableFragmentShader, Dispose, 1)                \
   V(ReusableFragmentShader, SetSampler, 3)             \
+  V(ReusableFragmentShader, ValidateSamplers, 1)       \
   V(Gradient, initLinear, 6)                           \
   V(Gradient, initRadial, 8)                           \
   V(Gradient, initSweep, 9)                            \

lib/ui/painting.dart

@@ -1409,6 +1409,14 @@ class Paint {
       );
       return true;
     }());
+    assert(() {
+      if (value is FragmentShader) {
+        if (!value._validateSamplers()) {
+          throw Exception('Invalid FragmentShader ${value._debugName ?? ''}: missing sampler');
+        }
+      }
+      return true;
+    }());
     _ensureObjectsInitialized()[_kShaderIndex] = value;
   }
 
@@ -4151,10 +4159,16 @@ class FragmentProgram extends NativeFieldWrapperClass1 {
     _constructor();
     final String result = _initFromAsset(assetKey);
     if (result.isNotEmpty) {
-      throw result; // ignore: only_throw_errors
+      throw Exception(result);
     }
+    assert(() {
+      _debugName = assetKey;
+      return true;
+    }());
   }
 
+  String? _debugName;
+
   // TODO(zra): Document custom shaders on the website and add a link to it
   // here. https://github.com/flutter/flutter/issues/107929.
   /// Creates a fragment program from the asset with key [assetKey].
@@ -4222,7 +4236,7 @@ class FragmentProgram extends NativeFieldWrapperClass1 {
   external String _initFromAsset(String assetKey);
 
   /// Returns a fresh instance of [FragmentShader].
-  FragmentShader fragmentShader() => FragmentShader._(this);
+  FragmentShader fragmentShader() => FragmentShader._(this, debugName: _debugName);
 }
 
 /// A [Shader] generated from a [FragmentProgram].
@@ -4239,17 +4253,18 @@ class FragmentProgram extends NativeFieldWrapperClass1 {
 /// are required to exist simultaneously, they must be obtained from two
 /// different calls to [FragmentProgram.fragmentShader].
 class FragmentShader extends Shader {
-  FragmentShader._(FragmentProgram program) : super._() {
+  FragmentShader._(FragmentProgram program, { String? debugName }) : _debugName = debugName, super._() {
     _floats = _constructor(
       program,
       program._uniformFloatCount,
       program._samplerCount,
     );
   }
 
-  static final Float32List _kEmptyFloat32List = Float32List(0);
+  final String? _debugName;
 
-  late Float32List _floats;
+  static final Float32List _kEmptyFloat32List = Float32List(0);
+  Float32List _floats = _kEmptyFloat32List;
 
   /// Sets the float uniform at [index] to [value].
   void setFloat(int index, double value) {
@@ -4284,6 +4299,9 @@ class FragmentShader extends Shader {
   @FfiNative<Void Function(Pointer<Void>, Handle, Handle)>('ReusableFragmentShader::SetSampler')
   external void _setSampler(int index, ImageShader sampler);
 
+  @FfiNative<Bool Function(Pointer<Void>)>('ReusableFragmentShader::ValidateSamplers')
+  external bool _validateSamplers();
+
   @FfiNative<Void Function(Pointer<Void>)>('ReusableFragmentShader::Dispose')
   external void _dispose();
 }

lib/ui/painting/fragment_program.cc

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <iostream>
 #include <memory>
 #include <sstream>
 
@@ -78,7 +77,6 @@ std::string FragmentProgram::initFromAsset(const std::string& asset_name) {
   if (Dart_IsError(ths)) {
     Dart_PropagateError(ths);
   }
-
   Dart_Handle result = Dart_SetField(ths, tonic::ToDart("_samplerCount"),
                                      Dart_NewInteger(sampled_image_count));
   if (Dart_IsError(result)) {

lib/ui/painting/fragment_shader.cc

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <iostream>
 #include <memory>
 #include <utility>
 
@@ -53,6 +52,15 @@ Dart_Handle ReusableFragmentShader::Create(Dart_Handle wrapper,
                                    float_count);
 }
 
+bool ReusableFragmentShader::ValidateSamplers() {
+  for (auto i = 0u; i < samplers_.size(); i += 1) {
+    if (samplers_[i] == nullptr) {
+      return false;
+    }
+  }
+  return true;
+}
+
 void ReusableFragmentShader::SetSampler(Dart_Handle index_handle,
                                         Dart_Handle sampler_handle) {
   uint64_t index = tonic::DartConverter<uint64_t>::FromDart(index_handle);

lib/ui/painting/fragment_shader.h

@@ -36,6 +36,8 @@ class ReusableFragmentShader : public Shader {
 
   void SetSampler(Dart_Handle index, Dart_Handle sampler);
 
+  bool ValidateSamplers();
+
   void Dispose();
 
   // |Shader|

testing/dart/fragment_shader_test.dart

@@ -62,6 +62,25 @@ void main() async {
     }
   });
 
+  test('FragmentShader with sampler asserts if sampler is missing when assigned to paint', () async {
+    if (!assertsEnabled) {
+      return;
+    }
+    final FragmentProgram program = await FragmentProgram.fromAsset(
+      'blue_green_sampler.frag.iplr',
+    );
+    final FragmentShader fragmentShader = program.fragmentShader();
+
+    try {
+      Paint().shader = fragmentShader;
+      fail('Expected to throw');
+    } catch (err) {
+      expect(err.toString(), contains('Invalid FragmentShader blue_green_sampler.frag.iplr'));
+    } finally {
+      fragmentShader.dispose();
+    }
+  });
+
   test('Disposed FragmentShader on Paint', () async {
     final FragmentProgram program = await FragmentProgram.fromAsset(
       'blue_green_sampler.frag.iplr',