packages/flutter/lib/src/rendering/texture.dart

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/foundation.dart';
import 'box.dart';
import 'layer.dart';
import 'object.dart';

/// A rectangle upon which a backend texture is mapped.
///
/// Backend textures are images that can be applied (mapped) to an area of the
/// Flutter view. They are created, managed, and updated using a
/// platform-specific texture registry. This is typically done by a plugin
/// that integrates with host platform video player, camera, or OpenGL APIs,
/// or similar image sources.
///
/// A texture box refers to its backend texture using an integer ID. Texture
/// IDs are obtained from the texture registry and are scoped to the Flutter
/// view. Texture IDs may be reused after deregistration, at the discretion
/// of the registry. The use of texture IDs currently unknown to the registry
/// will silently result in a blank rectangle.
///
/// Texture boxes are repainted autonomously as dictated by the backend (e.g. on
/// arrival of a video frame). Such repainting generally does not involve
/// executing Dart code.
///
/// The size of the rectangle is determined by the parent, and the texture is
/// automatically scaled to fit.
///
/// See also:
///
/// * <https://docs.flutter.io/javadoc/io/flutter/view/TextureRegistry.html>
///   for how to create and manage backend textures on Android.
/// * <https://docs.flutter.io/objcdoc/Protocols/FlutterTextureRegistry.html>
///   for how to create and manage backend textures on iOS.
class TextureBox extends RenderBox {
  /// Creates a box backed by the texture identified by [textureId].
  TextureBox({ @required int textureId }) : assert(textureId != null), _textureId = textureId;

  /// The identity of the backend texture.
  int get textureId => _textureId;
  int _textureId;
  set textureId(int value) {
    assert(value != null);
    if (value != _textureId) {
      _textureId = value;
      markNeedsPaint();
    }
  }

  @override
  bool get sizedByParent => true;

  @override
  bool get alwaysNeedsCompositing => true;

  @override
  bool get isRepaintBoundary => true;

  @override
  void performResize() {
    size = constraints.biggest;
  }

  @override
  bool hitTestSelf(Offset position) {
    return true;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (_textureId == null)
      return;
    context.addLayer(new TextureLayer(
      rect: new Rect.fromLTWH(offset.dx, offset.dy, size.width, size.height),
      textureId: _textureId,
    ));
  }
}