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// Copyright 2015 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 'dart:async';
import 'dart:ui' as ui show Image, Codec, FrameInfo;
import 'dart:ui' show hashValues;
import 'package:flutter/foundation.dart';
import 'package:flutter/scheduler.dart';
/// A [dart:ui.Image] object with its corresponding scale.
///
/// ImageInfo objects are used by [ImageStream] objects to represent the
/// actual data of the image once it has been obtained.
@immutable
class ImageInfo {
/// Creates an [ImageInfo] object for the given image and scale.
///
/// Both the image and the scale must not be null.
const ImageInfo({ @required this.image, this.scale = 1.0 })
: assert(image != null),
assert(scale != null);
/// The raw image pixels.
///
/// This is the object to pass to the [Canvas.drawImage],
/// [Canvas.drawImageRect], or [Canvas.drawImageNine] methods when painting
/// the image.
final ui.Image image;
/// The linear scale factor for drawing this image at its intended size.
///
/// The scale factor applies to the width and the height.
///
/// For example, if this is 2.0 it means that there are four image pixels for
/// every one logical pixel, and the image's actual width and height (as given
/// by the [dart:ui.Image.width] and [dart:ui.Image.height] properties) are double the
/// height and width that should be used when painting the image (e.g. in the
/// arguments given to [Canvas.drawImage]).
final double scale;
@override
String toString() => '$image @ ${scale}x';
@override
int get hashCode => hashValues(image, scale);
@override
bool operator ==(Object other) {
if (other.runtimeType != runtimeType)
return false;
final ImageInfo typedOther = other;
return typedOther.image == image
&& typedOther.scale == scale;
}
}
/// Signature for callbacks reporting that an image is available.
///
/// Used by [ImageStream].
///
/// The `synchronousCall` argument is true if the listener is being invoked
/// during the call to `addListener`. This can be useful if, for example,
/// [ImageStream.addListener] is invoked during a frame, so that a new rendering
/// frame is requested if the call was asynchronous (after the current frame)
/// and no rendering frame is requested if the call was synchronous (within the
/// same stack frame as the call to [ImageStream.addListener]).
typedef ImageListener = void Function(ImageInfo image, bool synchronousCall);
/// Signature for reporting errors when resolving images.
///
/// Used by [ImageStream] and [precacheImage] to report errors.
typedef ImageErrorListener = void Function(dynamic exception, StackTrace stackTrace);
class _ImageListenerPair {
_ImageListenerPair(this.listener, this.errorListener);
final ImageListener listener;
final ImageErrorListener errorListener;
}
/// A handle to an image resource.
///
/// ImageStream represents a handle to a [dart:ui.Image] object and its scale
/// (together represented by an [ImageInfo] object). The underlying image object
/// might change over time, either because the image is animating or because the
/// underlying image resource was mutated.
///
/// ImageStream objects can also represent an image that hasn't finished
/// loading.
///
/// ImageStream objects are backed by [ImageStreamCompleter] objects.
///
/// See also:
///
/// * [ImageProvider], which has an example that includes the use of an
/// [ImageStream] in a [Widget].
class ImageStream extends Diagnosticable {
/// Create an initially unbound image stream.
///
/// Once an [ImageStreamCompleter] is available, call [setCompleter].
ImageStream();
/// The completer that has been assigned to this image stream.
///
/// Generally there is no need to deal with the completer directly.
ImageStreamCompleter get completer => _completer;
ImageStreamCompleter _completer;
List<_ImageListenerPair> _listeners;
/// Assigns a particular [ImageStreamCompleter] to this [ImageStream].
///
/// This is usually done automatically by the [ImageProvider] that created the
/// [ImageStream].
///
/// This method can only be called once per stream. To have an [ImageStream]
/// represent multiple images over time, assign it a completer that
/// completes several images in succession.
void setCompleter(ImageStreamCompleter value) {
assert(_completer == null);
_completer = value;
if (_listeners != null) {
final List<_ImageListenerPair> initialListeners = _listeners;
_listeners = null;
for (_ImageListenerPair listenerPair in initialListeners) {
_completer.addListener(
listenerPair.listener,
onError: listenerPair.errorListener,
);
}
}
}
/// Adds a listener callback that is called whenever a new concrete [ImageInfo]
/// object is available. If a concrete image is already available, this object
/// will call the listener synchronously.
///
/// If the assigned [completer] completes multiple images over its lifetime,
/// this listener will fire multiple times.
///
/// The listener will be passed a flag indicating whether a synchronous call
/// occurred. If the listener is added within a render object paint function,
/// then use this flag to avoid calling [RenderObject.markNeedsPaint] during
/// a paint.
///
/// An [ImageErrorListener] can also optionally be added along with the
/// `listener`. If an error occurred, `onError` will be called instead of
/// `listener`.
///
/// If a `listener` or `onError` handler is registered multiple times, then it
/// will be called multiple times when the image stream completes (whether
/// because a new image is available or because an error occurs,
/// respectively). In general, registering a listener multiple times is
/// discouraged because [removeListener] will remove the first instance that
/// was added, even if it was added with a different `onError` than the
/// intended paired `addListener` call.
void addListener(ImageListener listener, { ImageErrorListener onError }) {
if (_completer != null)
return _completer.addListener(listener, onError: onError);
_listeners ??= <_ImageListenerPair>[];
_listeners.add(_ImageListenerPair(listener, onError));
}
/// Stop listening for new concrete [ImageInfo] objects and errors from
/// the `listener`'s associated [ImageErrorListener].
///
/// If `listener` has been added multiple times, this removes the first
/// instance of the listener, along with the `onError` listener that was
/// registered with that first instance. This might not be the instance that
/// the `addListener` corresponding to this `removeListener` had added.
///
/// For example, if one widget calls [addListener] with a global static
/// function and a private error handler, and another widget calls
/// [addListener] with the same global static function but a different private
/// error handler, then the second widget is disposed and removes the image
/// listener (the aforementioned global static function), it will remove the
/// error handler from the first widget, not the second. If an error later
/// occurs, the first widget, which is still supposedly listening, will not
/// receive any messages, while the second, which is supposedly disposed, will
/// have its callback invoked.
void removeListener(ImageListener listener) {
if (_completer != null)
return _completer.removeListener(listener);
assert(_listeners != null);
for (int i = 0; i < _listeners.length; i += 1) {
if (_listeners[i].listener == listener) {
_listeners.removeAt(i);
break;
}
}
}
/// Returns an object which can be used with `==` to determine if this
/// [ImageStream] shares the same listeners list as another [ImageStream].
///
/// This can be used to avoid un-registering and re-registering listeners
/// after calling [ImageProvider.resolve] on a new, but possibly equivalent,
/// [ImageProvider].
///
/// The key may change once in the lifetime of the object. When it changes, it
/// will go from being different than other [ImageStream]'s keys to
/// potentially being the same as others'. No notification is sent when this
/// happens.
Object get key => _completer != null ? _completer : this;
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(ObjectFlagProperty<ImageStreamCompleter>(
'completer',
_completer,
ifPresent: _completer?.toStringShort(),
ifNull: 'unresolved',
));
properties.add(ObjectFlagProperty<List<_ImageListenerPair>>(
'listeners',
_listeners,
ifPresent: '${_listeners?.length} listener${_listeners?.length == 1 ? "" : "s" }',
ifNull: 'no listeners',
level: _completer != null ? DiagnosticLevel.hidden : DiagnosticLevel.info,
));
_completer?.debugFillProperties(properties);
}
}
/// Base class for those that manage the loading of [dart:ui.Image] objects for
/// [ImageStream]s.
///
/// [ImageStreamListener] objects are rarely constructed directly. Generally, an
/// [ImageProvider] subclass will return an [ImageStream] and automatically
/// configure it with the right [ImageStreamCompleter] when possible.
abstract class ImageStreamCompleter extends Diagnosticable {
final List<_ImageListenerPair> _listeners = <_ImageListenerPair>[];
ImageInfo _currentImage;
FlutterErrorDetails _currentError;
/// Whether any listeners are currently registered.
///
/// Clients should not depend on this value for their behavior, because having
/// one listener's logic change when another listener happens to start or stop
/// listening will lead to extremely hard-to-track bugs. Subclasses might use
/// this information to determine whether to do any work when there are no
/// listeners, however; for example, [MultiFrameImageStreamCompleter] uses it
/// to determine when to iterate through frames of an animated image.
///
/// Typically this is used by overriding [addListener], checking if
/// [hasListeners] is false before calling `super.addListener()`, and if so,
/// starting whatever work is needed to determine when to call
/// [notifyListeners]; and similarly, by overriding [removeListener], checking
/// if [hasListeners] is false after calling `super.removeListener()`, and if
/// so, stopping that same work.
@protected
bool get hasListeners => _listeners.isNotEmpty;
/// Adds a listener callback that is called whenever a new concrete [ImageInfo]
/// object is available or an error is reported. If a concrete image is
/// already available, or if an error has been already reported, this object
/// will call the listener or error listener synchronously.
///
/// If the [ImageStreamCompleter] completes multiple images over its lifetime,
/// this listener will fire multiple times.
///
/// The listener will be passed a flag indicating whether a synchronous call
/// occurred. If the listener is added within a render object paint function,
/// then use this flag to avoid calling [RenderObject.markNeedsPaint] during
/// a paint.
///
/// An [ImageErrorListener] can also optionally be added along with the
/// `listener`. If an error occurred, `onError` will be called instead of
/// `listener`.
///
/// If a `listener` or `onError` handler is registered multiple times, then it
/// will be called multiple times when the image stream completes (whether
/// because a new image is available or because an error occurs,
/// respectively). In general, registering a listener multiple times is
/// discouraged because [removeListener] will remove the first instance that
/// was added, even if it was added with a different `onError` than the
/// intended paired `addListener` call.
void addListener(ImageListener listener, { ImageErrorListener onError }) {
_listeners.add(_ImageListenerPair(listener, onError));
if (_currentImage != null) {
try {
listener(_currentImage, true);
} catch (exception, stack) {
reportError(
context: 'by a synchronously-called image listener',
exception: exception,
stack: stack,
);
}
}
if (_currentError != null && onError != null) {
try {
onError(_currentError.exception, _currentError.stack);
} catch (exception, stack) {
FlutterError.reportError(
FlutterErrorDetails(
exception: exception,
library: 'image resource service',
context: 'by a synchronously-called image error listener',
stack: stack,
),
);
}
}
}
/// Stop listening for new concrete [ImageInfo] objects and errors from
/// its associated [ImageErrorListener].
///
/// If `listener` has been added multiple times, this removes the first
/// instance of the listener, along with the `onError` listener that was
/// registered with that first instance. This might not be the instance that
/// the `addListener` corresponding to this `removeListener` had added.
void removeListener(ImageListener listener) {
for (int i = 0; i < _listeners.length; i += 1) {
if (_listeners[i].listener == listener) {
_listeners.removeAt(i);
break;
}
}
}
/// Calls all the registered listeners to notify them of a new image.
@protected
void setImage(ImageInfo image) {
_currentImage = image;
if (_listeners.isEmpty)
return;
final List<ImageListener> localListeners = _listeners.map<ImageListener>(
(_ImageListenerPair listenerPair) => listenerPair.listener
).toList();
for (ImageListener listener in localListeners) {
try {
listener(image, false);
} catch (exception, stack) {
reportError(
context: 'by an image listener',
exception: exception,
stack: stack,
);
}
}
}
/// Calls all the registered error listeners to notify them of an error that
/// occurred while resolving the image.
///
/// If no error listeners are attached, a [FlutterError] will be reported
/// instead.
///
/// The `context` should be a string describing where the error was caught, in
/// a form that will make sense in English when following the word "thrown",
/// as in "thrown while obtaining the image from the network" (for the context
/// "while obtaining the image from the network").
///
/// The `exception` is the error being reported; the `stack` is the
/// [StackTrace] associated with the exception.
///
/// The `informationCollector` is a callback (of type [InformationCollector])
/// that is called when the exception is used by [FlutterError.reportError].
/// It is used to obtain further details to include in the logs, which may be
/// expensive to collect, and thus should only be collected if the error is to
/// be logged in the first place.
///
/// The `silent` argument causes the exception to not be reported to the logs
/// in release builds, if passed to [FlutterError.reportError]. (It is still
/// sent to error handlers.) It should be set to true if the error is one that
/// is expected to be encountered in release builds, for example network
/// errors. That way, logs on end-user devices will not have spurious
/// messages, but errors during development will still be reported.
///
/// See [FlutterErrorDetails] for further details on these values.
@protected
void reportError({
String context,
dynamic exception,
StackTrace stack,
InformationCollector informationCollector,
bool silent = false,
}) {
_currentError = FlutterErrorDetails(
exception: exception,
stack: stack,
library: 'image resource service',
context: context,
informationCollector: informationCollector,
silent: silent,
);
final List<ImageErrorListener> localErrorListeners =
_listeners.map<ImageErrorListener>(
(_ImageListenerPair listenerPair) => listenerPair.errorListener
).where(
(ImageErrorListener errorListener) => errorListener != null
).toList();
if (localErrorListeners.isEmpty) {
FlutterError.reportError(_currentError);
} else {
for (ImageErrorListener errorListener in localErrorListeners) {
try {
errorListener(exception, stack);
} catch (exception, stack) {
FlutterError.reportError(
FlutterErrorDetails(
context: 'when reporting an error to an image listener',
library: 'image resource service',
exception: exception,
stack: stack,
),
);
}
}
}
}
/// Accumulates a list of strings describing the object's state. Subclasses
/// should override this to have their information included in [toString].
@override
void debugFillProperties(DiagnosticPropertiesBuilder description) {
super.debugFillProperties(description);
description.add(DiagnosticsProperty<ImageInfo>('current', _currentImage, ifNull: 'unresolved', showName: false));
description.add(ObjectFlagProperty<List<_ImageListenerPair>>(
'listeners',
_listeners,
ifPresent: '${_listeners?.length} listener${_listeners?.length == 1 ? "" : "s" }',
));
}
}
/// Manages the loading of [dart:ui.Image] objects for static [ImageStream]s (those
/// with only one frame).
class OneFrameImageStreamCompleter extends ImageStreamCompleter {
/// Creates a manager for one-frame [ImageStream]s.
///
/// The image resource awaits the given [Future]. When the future resolves,
/// it notifies the [ImageListener]s that have been registered with
/// [addListener].
///
/// The [InformationCollector], if provided, is invoked if the given [Future]
/// resolves with an error, and can be used to supplement the reported error
/// message (for example, giving the image's URL).
///
/// Errors are reported using [FlutterError.reportError] with the `silent`
/// argument on [FlutterErrorDetails] set to true, meaning that by default the
/// message is only dumped to the console in debug mode (see [new
/// FlutterErrorDetails]).
OneFrameImageStreamCompleter(Future<ImageInfo> image, { InformationCollector informationCollector })
: assert(image != null) {
image.then<void>(setImage, onError: (dynamic error, StackTrace stack) {
reportError(
context: 'resolving a single-frame image stream',
exception: error,
stack: stack,
informationCollector: informationCollector,
silent: true,
);
});
}
}
/// Manages the decoding and scheduling of image frames.
///
/// New frames will only be emitted while there are registered listeners to the
/// stream (registered with [addListener]).
///
/// This class deals with 2 types of frames:
///
/// * image frames - image frames of an animated image.
/// * app frames - frames that the flutter engine is drawing to the screen to
/// show the app GUI.
///
/// For single frame images the stream will only complete once.
///
/// For animated images, this class eagerly decodes the next image frame,
/// and notifies the listeners that a new frame is ready on the first app frame
/// that is scheduled after the image frame duration has passed.
///
/// Scheduling new timers only from scheduled app frames, makes sure we pause
/// the animation when the app is not visible (as new app frames will not be
/// scheduled).
///
/// See the following timeline example:
///
/// | Time | Event | Comment |
/// |------|--------------------------------------------|---------------------------|
/// | t1 | App frame scheduled (image frame A posted) | |
/// | t2 | App frame scheduled | |
/// | t3 | App frame scheduled | |
/// | t4 | Image frame B decoded | |
/// | t5 | App frame scheduled | t5 - t1 < frameB_duration |
/// | t6 | App frame scheduled (image frame B posted) | t6 - t1 > frameB_duration |
///
class MultiFrameImageStreamCompleter extends ImageStreamCompleter {
/// Creates a image stream completer.
///
/// Immediately starts decoding the first image frame when the codec is ready.
///
/// [codec] is a future for an initialized [ui.Codec] that will be used to
/// decode the image.
/// [scale] is the linear scale factor for drawing this frames of this image
/// at their intended size.
MultiFrameImageStreamCompleter({
@required Future<ui.Codec> codec,
@required double scale,
InformationCollector informationCollector,
}) : assert(codec != null),
_informationCollector = informationCollector,
_scale = scale {
codec.then<void>(_handleCodecReady, onError: (dynamic error, StackTrace stack) {
reportError(
context: 'resolving an image codec',
exception: error,
stack: stack,
informationCollector: informationCollector,
silent: true,
);
});
}
ui.Codec _codec;
final double _scale;
final InformationCollector _informationCollector;
ui.FrameInfo _nextFrame;
// When the current was first shown.
Duration _shownTimestamp;
// The requested duration for the current frame;
Duration _frameDuration;
// How many frames have been emitted so far.
int _framesEmitted = 0;
Timer _timer;
// Used to guard against registering multiple _handleAppFrame callbacks for the same frame.
bool _frameCallbackScheduled = false;
void _handleCodecReady(ui.Codec codec) {
_codec = codec;
assert(_codec != null);
if (hasListeners) {
_decodeNextFrameAndSchedule();
}
}
void _handleAppFrame(Duration timestamp) {
_frameCallbackScheduled = false;
if (!hasListeners)
return;
if (_isFirstFrame() || _hasFrameDurationPassed(timestamp)) {
_emitFrame(ImageInfo(image: _nextFrame.image, scale: _scale));
_shownTimestamp = timestamp;
_frameDuration = _nextFrame.duration;
_nextFrame = null;
final int completedCycles = _framesEmitted ~/ _codec.frameCount;
if (_codec.repetitionCount == -1 || completedCycles <= _codec.repetitionCount) {
_decodeNextFrameAndSchedule();
}
return;
}
final Duration delay = _frameDuration - (timestamp - _shownTimestamp);
_timer = Timer(delay * timeDilation, () {
_scheduleAppFrame();
});
}
bool _isFirstFrame() {
return _frameDuration == null;
}
bool _hasFrameDurationPassed(Duration timestamp) {
assert(_shownTimestamp != null);
return timestamp - _shownTimestamp >= _frameDuration;
}
Future<void> _decodeNextFrameAndSchedule() async {
try {
_nextFrame = await _codec.getNextFrame();
} catch (exception, stack) {
reportError(
context: 'resolving an image frame',
exception: exception,
stack: stack,
informationCollector: _informationCollector,
silent: true,
);
return;
}
if (_codec.frameCount == 1) {
// This is not an animated image, just return it and don't schedule more
// frames.
_emitFrame(ImageInfo(image: _nextFrame.image, scale: _scale));
return;
}
_scheduleAppFrame();
}
void _scheduleAppFrame() {
if (_frameCallbackScheduled) {
return;
}
_frameCallbackScheduled = true;
SchedulerBinding.instance.scheduleFrameCallback(_handleAppFrame);
}
void _emitFrame(ImageInfo imageInfo) {
setImage(imageInfo);
_framesEmitted += 1;
}
@override
void addListener(ImageListener listener, { ImageErrorListener onError }) {
if (!hasListeners && _codec != null)
_decodeNextFrameAndSchedule();
super.addListener(listener, onError: onError);
}
@override
void removeListener(ImageListener listener) {
super.removeListener(listener);
if (!hasListeners) {
_timer?.cancel();
_timer = null;
}
}
}