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Add a Display API to dart:ui that reports the physical size, DPR, and refresh rate of the main display #41685

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May 6, 2023
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Add a Display API to dart:ui that reports the physical size, DPR, and refresh rate of the main display #41685

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38c8574
start
dnfield Mar 23, 2023
5c6f70e
Merge remote-tracking branch 'upstream/main' into displays
dnfield May 2, 2023
91d7e81
Report display sizes for mobile to Flutter
dnfield May 3, 2023
7b9f681
web
dnfield May 3, 2023
878dcfb
Cleanup, tests for Android/Host/Hooks
dnfield May 3, 2023
6f1a0bb
scenario app
dnfield May 3, 2023
123deaf
oops
dnfield May 3, 2023
d0224c9
One more DCHECK
dnfield May 3, 2023
67958ed
web, fucshia build failures
dnfield May 3, 2023
04418a4
Merge remote-tracking branch 'upstream/main' into displays
dnfield May 3, 2023
3e87708
one more spot for Fuchsia
dnfield May 3, 2023
806a4ae
lint
dnfield May 3, 2023
5f2e0c1
accidental change
dnfield May 3, 2023
be4731d
Once more, with feeling
dnfield May 3, 2023
200f091
Tidying, last Fuchsia test compilation issue
dnfield May 3, 2023
ea76da6
Loic review
dnfield May 3, 2023
fc3b8f4
Fix failing test, add unit test for FlutterEngine.mm
dnfield May 4, 2023
8f62507
try to find test failure
dnfield May 4, 2023
ad25b20
fix test
dnfield May 4, 2023
a7602b4
docs
dnfield May 4, 2023
40bb6c9
Merge branch 'main' into displays
dnfield May 4, 2023
1f2e889
Merge remote-tracking branch 'upstream/main' into displays
dnfield May 6, 2023
400b50a
docs
dnfield May 6, 2023
9df181c
Merge branch 'displays' of github.com:dnfield/engine into displays
dnfield May 6, 2023
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1 change: 1 addition & 0 deletions lib/ui/BUILD.gn
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Original file line number Diff line number Diff line change
Expand Up @@ -163,6 +163,7 @@ source_set("ui") {

public_deps = [
"//flutter/flow",
"//flutter/shell/common:display",
"//flutter/shell/common:platform_message_handler",
"//flutter/third_party/txt",
]
Expand Down
43 changes: 36 additions & 7 deletions lib/ui/fixtures/ui_test.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ import 'dart:async';
import 'dart:typed_data';
import 'dart:ui';
import 'dart:isolate';
import 'dart:ffi';
import 'dart:ffi' hide Size;

void main() {}

Expand Down Expand Up @@ -444,7 +444,7 @@ void hooksTests() async {
window.onMetricsChanged!();
_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
0.1234, // device pixel ratio
0.0, // width
Expand All @@ -465,6 +465,7 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectIdentical(originalZone, callbackZone);
Expand Down Expand Up @@ -540,7 +541,7 @@ void hooksTests() async {
await test('View padding/insets/viewPadding/systemGestureInsets', () {
_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
1.0, // devicePixelRatio
800.0, // width
Expand All @@ -561,6 +562,7 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectEquals(window.viewInsets.bottom, 0.0);
Expand All @@ -570,7 +572,7 @@ void hooksTests() async {

_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
1.0, // devicePixelRatio
800.0, // width
Expand All @@ -591,6 +593,7 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectEquals(window.viewInsets.bottom, 400.0);
Expand All @@ -602,7 +605,7 @@ void hooksTests() async {
await test('Window physical touch slop', () {
_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
1.0, // devicePixelRatio
800.0, // width
Expand All @@ -623,14 +626,15 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectEquals(window.gestureSettings,
GestureSettings(physicalTouchSlop: 11.0));

_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
1.0, // devicePixelRatio
800.0, // width
Expand All @@ -651,14 +655,15 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectEquals(window.gestureSettings,
GestureSettings(physicalTouchSlop: null));

_callHook(
'_updateWindowMetrics',
20,
21,
0, // window Id
1.0, // devicePixelRatio
800.0, // width
Expand All @@ -679,6 +684,7 @@ void hooksTests() async {
<double>[], // display features bounds
<int>[], // display features types
<int>[], // display features states
0, // Display ID
);

expectEquals(window.gestureSettings,
Expand Down Expand Up @@ -881,6 +887,28 @@ void hooksTests() async {
expectEquals(frameNumber, 2);
});

await test('_updateDisplays preserves callback zone', () {
late Zone innerZone;
late Zone runZone;
late Display display;

runZoned(() {
innerZone = Zone.current;
window.onMetricsChanged = () {
runZone = Zone.current;
display = PlatformDispatcher.instance.displays.first;
};
});

_callHook('_updateDisplays', 5, <int>[0], <double>[800], <double>[600], <double>[1.5], <double>[65]);
expectNotEquals(runZone, null);
expectIdentical(runZone, innerZone);
expectEquals(display.id, 0);
expectEquals(display.size, const Size(800, 600));
expectEquals(display.devicePixelRatio, 1.5);
expectEquals(display.refreshRate, 65);
});

await test('_futureize handles callbacker sync error', () async {
String? callbacker(void Function(Object? arg) cb) {
return 'failure';
Expand Down Expand Up @@ -1043,4 +1071,5 @@ external void _callHook(
Object? arg18,
Object? arg19,
Object? arg20,
Object? arg21,
]);
28 changes: 28 additions & 0 deletions lib/ui/hooks.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,32 @@

part of dart.ui;

@pragma('vm:entry-point')
void _updateDisplays(
List<int> ids,
List<double> widths,
List<double> heights,
List<double> devicePixelRatios,
List<double> refreshRates,
) {
assert(ids.length == widths.length);
assert(ids.length == heights.length);
assert(ids.length == devicePixelRatios.length);
assert(ids.length == refreshRates.length);
final List<Display> displays = <Display>[];
for (int index = 0; index < ids.length; index += 1) {
final int displayId = ids[index];
displays.add(Display._(
id: displayId,
size: Size(widths[index], heights[index]),
devicePixelRatio: devicePixelRatios[index],
refreshRate: refreshRates[index],
));
}

PlatformDispatcher.instance._updateDisplays(displays);
}

@pragma('vm:entry-point')
void _updateWindowMetrics(
Object id,
Expand All @@ -26,6 +52,7 @@ void _updateWindowMetrics(
List<double> displayFeaturesBounds,
List<int> displayFeaturesType,
List<int> displayFeaturesState,
int displayId,
) {
PlatformDispatcher.instance._updateWindowMetrics(
id,
Expand All @@ -48,6 +75,7 @@ void _updateWindowMetrics(
displayFeaturesBounds,
displayFeaturesType,
displayFeaturesState,
displayId,
);
}

Expand Down
40 changes: 40 additions & 0 deletions lib/ui/platform_dispatcher.dart
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Expand Up @@ -149,6 +149,26 @@ class PlatformDispatcher {
_onPlatformConfigurationChangedZone = Zone.current;
}

/// The current list of displays.
///
/// If any of their configurations change, [onMetricsChanged] will be called.
///
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@goderbauer goderbauer May 4, 2023

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Maybe document some of the current platform-specific limitations? Presumably, this is just empty for desktops right now?

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@dnfield dnfield May 4, 2023

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I added some docs.

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@goderbauer goderbauer May 4, 2023

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The same caveat should likely also be documented on the FlutterView.display property?

/// To get the display for a [FlutterView], use [FlutterView.display].
///
/// Platforms may limit what information is available to the application with
/// regard to secondary displays and/or displays that do not have an active
/// application window.
///
/// Presently, on Android and Web this collection will only contain the
/// display that the current window is on. On iOS, it will only contains the
/// main display on the phone or tablet. On Desktop, it will contain only
/// a main display with a valid refresh rate but invalid size and device
/// pixel ratio values.
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@reidbaker reidbaker May 5, 2023

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Is it possible to make these values missing or null instead of invalid (which I assume means incorrect).

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@dnfield dnfield May 6, 2023

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I don't want to make them null, since it will be harder to migrate them away from nullable later if people start treating them as nullable (e.g. they add ! all over and the compiler refuses to compiile things when we switch it).

The plan is to implement them for desktop sooner than later.

// TODO(dnfield): Update these docs when https://github.com/flutter/flutter/issues/125939
// and https://github.com/flutter/flutter/issues/125938 are resolved.
Iterable<Display> get displays => _displays.values;
final Map<int, Display> _displays = <int, Display>{};

/// The current list of views, including top level platform windows used by
/// the application.
///
Expand Down Expand Up @@ -215,6 +235,17 @@ class PlatformDispatcher {
_onMetricsChangedZone = Zone.current;
}

// Called from the engine, via hooks.dart.
//
// Updates the available displays.
void _updateDisplays(List<Display> displays) {
_displays.clear();
for (final Display display in displays) {
_displays[display.id] = display;
}
_invoke(onMetricsChanged, _onMetricsChangedZone);
}

// Called from the engine, via hooks.dart
//
// Updates the metrics of the window with the given id.
Expand All @@ -239,6 +270,7 @@ class PlatformDispatcher {
List<double> displayFeaturesBounds,
List<int> displayFeaturesType,
List<int> displayFeaturesState,
int displayId,
) {
final _ViewConfiguration previousConfiguration =
_viewConfigurations[id] ?? const _ViewConfiguration();
Expand Down Expand Up @@ -283,6 +315,7 @@ class PlatformDispatcher {
state: displayFeaturesState,
devicePixelRatio: devicePixelRatio,
),
displayId: displayId,
);
_invoke(onMetricsChanged, _onMetricsChangedZone);
}
Expand Down Expand Up @@ -1318,6 +1351,7 @@ class _ViewConfiguration {
this.padding = ViewPadding.zero,
this.gestureSettings = const GestureSettings(),
this.displayFeatures = const <DisplayFeature>[],
this.displayId = 0,
});

/// Copy this configuration with some fields replaced.
Expand All @@ -1332,6 +1366,7 @@ class _ViewConfiguration {
ViewPadding? padding,
GestureSettings? gestureSettings,
List<DisplayFeature>? displayFeatures,
int? displayId,
}) {
return _ViewConfiguration(
view: view ?? this.view,
Expand All @@ -1344,11 +1379,16 @@ class _ViewConfiguration {
padding: padding ?? this.padding,
gestureSettings: gestureSettings ?? this.gestureSettings,
displayFeatures: displayFeatures ?? this.displayFeatures,
displayId: displayId ?? this.displayId,
);
}

final FlutterView? view;

/// The identifier for a display for this view, in
/// [PlatformDispatcher._displays].
final int displayId;

/// The pixel density of the output surface.
final double devicePixelRatio;

Expand Down
42 changes: 42 additions & 0 deletions lib/ui/window.dart
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Expand Up @@ -3,6 +3,40 @@
// found in the LICENSE file.
part of dart.ui;

/// A configurable display that a [FlutterView] renders on.
///
/// Use [FlutterView.display] to get the current display for that view.
class Display {
const Display._({
required this.id,
required this.devicePixelRatio,
required this.size,
required this.refreshRate,
});

/// A unique identifier for this display.
///
/// This identifier is unique among a list of displays the Flutter framework
/// is aware of, and is not derived from any platform specific identifiers for
/// displays.
final int id;

/// The device pixel ratio of this display.
///
/// This value is the same as the value of [FlutterView.devicePixelRatio] for
/// all view objects attached to this display.
final double devicePixelRatio;

/// The physical size of this display.
final Size size;

/// The refresh rate in FPS of this display.
final double refreshRate;

@override
String toString() => 'Display(id: $id, size: $size, devicePixelRatio: $devicePixelRatio, refreshRate: $refreshRate)';
}

/// A view into which a Flutter [Scene] is drawn.
///
/// Each [FlutterView] has its own layer tree that is rendered
Expand Down Expand Up @@ -67,6 +101,12 @@ class FlutterView {
return platformDispatcher._viewConfigurations[viewId]!;
}

/// The [Display] this view is drawn in.
Display get display {
assert(platformDispatcher._displays.containsKey(_viewConfiguration.displayId));
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@loic-sharma loic-sharma May 3, 2023 •
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Will this fail if the embedder doesn't provide display information? (I'm not sure Windows, macOS, or Linux provide display information)

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@dnfield dnfield May 3, 2023

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Right now they provide a display that is not quite valid. But yes, the assert would fire if the embedder failed to provide a display.

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@loic-sharma loic-sharma May 3, 2023

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Should we make this property nullable and force the caller to have some fallback logic if display information isn't available?

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@dnfield dnfield May 4, 2023

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I think we should just implement it. Making it nullable now and non-nullable later is harder once people start using it (it results in compilation errors, which make the migration in google's monorepo harder). I don't expect it to take long to implement the desktop portion of this, I just don't want to delay this patch further and it's already fairly large.

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@goderbauer goderbauer May 4, 2023

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So, what does this currently return for unimplemented platforms?

Have we verified that this is implementable on all desktop platforms we want to support? Wayland comes to mind as a platform that may not be able to tell us what display we are on (I haven't verified this, this is just from what I have heard). If that turns out to be true, what would we expect this getter to do? For that case, it may be nicer if this can just be null.

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@dnfield dnfield May 4, 2023

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Right now it's returning -1 for the DPR, width, and height, and a real refresh rate/display ID.

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@dnfield dnfield May 4, 2023

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On Linux, we can indeed get the width and height of at least the display the application is rendering to, and probably all displays. Even if Wayland doesn't have an API for this, you have to tell Wayland to connect to a particular display adapter, and it will be possible to query the information about the display size from that adapter. GTK also has an API for this.

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@goderbauer goderbauer May 4, 2023

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What's the GTK API?

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@dnfield dnfield May 4, 2023

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Sorry, I meant GDK :) What the Linux embedding uses for windowing etc.

return platformDispatcher._displays[_viewConfiguration.displayId]!;
}

/// The number of device pixels for each logical pixel for the screen this
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@goderbauer goderbauer May 4, 2023

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There is a little bit of duplicated information available now as dpr as also available via the display getter now. It's probably not an issue, but a little strange? Presumably, both will always have the same value?

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@dnfield dnfield May 4, 2023

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DPR really belongs on the display. I'm half tempted to deprecate it on View, but that seems like it'd create a lot of unnecessary churn.

But yes, DPR on the view will always match DPR from the display.

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@reidbaker reidbaker May 5, 2023

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You might want to add to the dart doc to DPR on view that says window is the prefered way if you indeed think that is the case.

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@dnfield dnfield May 6, 2023

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You need the DPR if you want to figure out logical pixel sizes. I'll document that they're the same.

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@dnfield dnfield May 6, 2023

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Added some docs.

/// view is displayed on.
///
Expand All @@ -92,6 +132,8 @@ class FlutterView {
///
/// * [WidgetsBindingObserver], for a mechanism at the widgets layer to
/// observe when this value changes.
/// * [Display.devicePixelRatio], which reports the DPR of the display.
/// The value here is equal to the value on the [display.devicePixelRatio].
double get devicePixelRatio => _viewConfiguration.devicePixelRatio;

/// The dimensions and location of the rectangle into which the scene rendered
Expand Down
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