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https://github.com/flutter/flutter
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d927c93310
* enable lint unnecessary_new * fix tests * fix tests * fix tests
51 lines
2 KiB
Dart
51 lines
2 KiB
Dart
// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// This example shows how to show the text 'Hello, world.' using using the raw
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// interface to the engine.
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import 'dart:ui' as ui;
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void beginFrame(Duration timeStamp) {
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final double devicePixelRatio = ui.window.devicePixelRatio;
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final ui.Size logicalSize = ui.window.physicalSize / devicePixelRatio;
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final ui.ParagraphBuilder paragraphBuilder = ui.ParagraphBuilder(
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ui.ParagraphStyle(textDirection: ui.TextDirection.ltr),
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)
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..addText('Hello, world.');
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final ui.Paragraph paragraph = paragraphBuilder.build()
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..layout(ui.ParagraphConstraints(width: logicalSize.width));
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final ui.Rect physicalBounds = ui.Offset.zero & (logicalSize * devicePixelRatio);
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final ui.PictureRecorder recorder = ui.PictureRecorder();
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final ui.Canvas canvas = ui.Canvas(recorder, physicalBounds);
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canvas.scale(devicePixelRatio, devicePixelRatio);
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canvas.drawParagraph(paragraph, ui.Offset(
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(logicalSize.width - paragraph.maxIntrinsicWidth) / 2.0,
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(logicalSize.height - paragraph.height) / 2.0
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));
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final ui.Picture picture = recorder.endRecording();
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final ui.SceneBuilder sceneBuilder = ui.SceneBuilder()
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// TODO(abarth): We should be able to add a picture without pushing a
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// container layer first.
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..pushClipRect(physicalBounds)
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..addPicture(ui.Offset.zero, picture)
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..pop();
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ui.window.render(sceneBuilder.build());
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}
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// This function is the primary entry point to your application. The engine
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// calls main() as soon as it has loaded your code.
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void main() {
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// The engine calls onBeginFrame whenever it wants us to produce a frame.
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ui.window.onBeginFrame = beginFrame;
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// Here we kick off the whole process by asking the engine to schedule a new
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// frame. The engine will eventually call onBeginFrame when it is time for us
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// to actually produce the frame.
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ui.window.scheduleFrame();
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}
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