Dart Rotated Box

rotated_box.dart

import 'dart:math' as math;
import 'dart:typed_data';
import 'dart:ui' as ui;

void beginFrame(Duration timeStamp) {
    // The timeStamp argument to beginFrame indicates the timing information we
    // should use to clock our animations. It's important to use timeStamp rather
    // than reading the system time because we want all the parts of the system to
    // coordinate the timings of their animations. If each component read the
    // system clock independently, the animations that we processed later would be
    // slightly ahead of the animations we processed earlier.

    // PAINT

    final ui.Rect paintBounds = ui.Offset.zero & (ui.window.physicalSize / ui.window.devicePixelRatio);
    final ui.PictureRecorder recorder = ui.PictureRecorder();
    final ui.Canvas canvas = ui.Canvas(recorder, paintBounds);
    canvas.translate(paintBounds.width / 2.0, paintBounds.height / 2.0);

    // Here we determine the rotation according to the timeStamp given to us by
    // the engine.
    final double t = timeStamp.inMicroseconds / Duration.microsecondsPerMillisecond / 1800.0;
    canvas.rotate(math.pi * (t % 1.0) * 3);

    canvas.drawRect(ui.Rect.fromLTRB(-100.0, -100.0, 100.0, 100.0),
        ui.Paint()..color = const ui.Color.fromARGB(255, 0, 255, 0));
    final ui.Picture picture = recorder.endRecording();

    // COMPOSITE

    final double devicePixelRatio = ui.window.devicePixelRatio;
    final Float64List deviceTransform = Float64List(16)
        ..[0] = devicePixelRatio
        ..[5] = devicePixelRatio
        ..[10] = 1.0
        ..[15] = 1.0;
    final ui.SceneBuilder sceneBuilder = ui.SceneBuilder()
        ..pushTransform(deviceTransform)
        ..addPicture(ui.Offset.zero, picture)
        ..pop();
    ui.window.render(sceneBuilder.build());

    // After rendering the current frame of the animation, we ask the engine to
    // schedule another frame. The engine will call beginFrame again when its time
    // to produce the next frame.
    ui.window.scheduleFrame();
}

void main() {
    ui.window.onBeginFrame = beginFrame;
    ui.window.scheduleFrame();
}