animation - Android 上的 Flutter 动画 : D/skia (22985): Could not invert viewmatrix

Question

重现步骤

在不深入研究代码的情况下，每次时间变化时我都会触发一个动画，其中:

@override
Widget build(BuildContext context) {

    if (this._currentTime != widget.amountOfTime) {
      this._changeTimeAnimation();
    }

    return new AnimatedBuilder(
      animation: this._animation,
      builder: (BuildContext context, Widget child) => this._flipAnimation(child),
      child: new Text(
        this._currentTime,
        textAlign: TextAlign.left,
        style: new TextStyle(fontSize: 100.0),
      ),
    );
  }

this._flipAnimation() 如下:

Transform _flipAnimation(Widget child) {
    /// Function used to generate a flip animation for the time

    final Matrix4 transform = new Matrix4.identity()
      ..scale(1.0, this._animation.value, 1.0);

    return Transform(
      transform: transform,
      alignment: FractionalOffset.center,
      child: child,
    );
  }

每次触发动画时，我都会收到消息 D/skia (22985): Could not invert viewmatrix。这是为什么？

我会注意到，动画在设备上似乎运行良好，但打印输出很奇怪。

日志

在 flutter run 之后:

Performing full restart...
Restarted app in 2,182ms.
D/skia    (22985): Could not invert viewmatrix
D/skia    (22985): Could not invert viewmatrix
D/skia    (22985): Could not invert viewmatrix
D/skia    (22985): Could not invert viewmatrix
D/skia    (22985): Could not invert viewmatrix

flutter 医生

运行 flutter doctor -v 后:

[✓] Flutter (Channel beta, v0.2.8, on Mac OS X 10.13.4 17E199, locale en-US)
    • Flutter version 0.2.8 at /Users/jvanderen11/flutter
    • Framework revision b397406561 (13 days ago), 2018-04-02 13:53:20 -0700
    • Engine revision c903c217a1
    • Dart version 2.0.0-dev.43.0.flutter-52afcba357

[✓] Android toolchain - develop for Android devices (Android SDK
27.0.3)
    • Android SDK at /Users/jvanderen11/Library/Android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-27, build-tools 27.0.3
    • Java binary at: /Applications/Developer Tools/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 9.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 9.3, Build version 9E145
    • ios-deploy 1.9.2
    • CocoaPods version 1.5.0

[✓] Android Studio (version 3.1)
    • Android Studio at /Applications/Developer Tools/Android Studio.app/Contents
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] IntelliJ IDEA Ultimate Edition (version 2018.1.1)
    • IntelliJ at /Users/jvanderen11/Applications/JetBrains Toolbox/IntelliJ IDEA Ultimate.app
    • Flutter plugin version 23.1.3
    • Dart plugin version 181.4203.498

[✓] Connected devices (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 7.1.1 (API 25) (emulator)

• No issues found!

Answer 1

错误的原因是当缩放比例为 (1.0, 0.0, 1.0) 时，它会导致矩阵 Skia 不喜欢(可能无效 - 参见 where skia generates the error ，我认为是 the line where it causes the error )。

一个简单的解决方法是确保您从未真正通过 scale(1.0, 0.0, 1.0)，要么通过修改您的代码，要么每次都向数字中添加非常小的数量，即 ..scale(1.0, this._animation.value + smallval, 1.0)

显然 smallval=1e-100 太小了，因为它在为 skia 转换为 c++ 时丢失了，但是 smallval=0.00000000000000000000000000000000000000000000000001 确实有效。