flutter/packages/flutter/lib/src/widgets/_web_image_web.dart at master · flutter/flutter · GitHub

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// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

/// @docImport 'package:flutter/rendering.dart';

library;

import 'dart:ui_web' as ui_web;

import 'package:flutter/foundation.dart';

import '../painting/_web_image_info_web.dart';

import '../rendering/box.dart';

import '../rendering/platform_view.dart';

import '../rendering/shifted_box.dart';

import '../web.dart' as web;

import 'basic.dart';

import 'framework.dart';

import 'platform_view.dart';

/// Displays an `<img>` element with `src` set to [src].

class ImgElementPlatformView extends StatefulWidget {

/// Creates a platform view backed with an `<img>` element.

ImgElementPlatformView(this.src, {super.key}) {

if (!_registered) {

_register();

}

static const String _viewType = 'Flutter__ImgElementImage__';

static bool _registered = false;

static void _register() {

assert(!_registered);

_registered = true;

ui_web.platformViewRegistry.registerViewFactory(_viewType, (int viewId, {Object? params}) {

// Create a new <img> element. The browser is able to display the image

// without fetching it over the network again.

final img = web.document.createElement('img') as web.HTMLImageElement;

// Set `width` and `height`, otherwise the engine will issue a warning.

img.style

..width = '100%'

..height = '100%'

..pointerEvents = 'none';

return img;

});

}

/// The `src` URL for the `<img>` tag.

final String? src;

@override

State<ImgElementPlatformView> createState() => _ImgElementPlatformViewState();

}

class _ImgElementPlatformViewState extends State<ImgElementPlatformView> {

web.HTMLImageElement? _imgElement;

void _onPlatformViewCreated(int viewId) {

final img = ui_web.platformViewRegistry.getViewById(viewId) as web.HTMLImageElement;

// Platform view creation is asynchronous. If this State was already

// disposed (or widget.src became null) before the creation callback fired,

// clear the <img> element's src immediately.

if (!mounted || widget.src == null) {

img.src = '';

return;

}

_imgElement?.src = '';

_imgElement = img;

img.src = widget.src!;

}

@override

void didUpdateWidget(ImgElementPlatformView oldWidget) {

super.didUpdateWidget(oldWidget);

if (widget.src != oldWidget.src) {

if (widget.src == null) {

_imgElement?.src = '';

_imgElement = null;

} else {

_imgElement?.src = widget.src!;

}

@override

void dispose() {

// Clear the src attribute when the platform view is disposed so the browser

// can eagerly reclaim the decoded image buffer.

_imgElement?.src = '';

_imgElement = null;

super.dispose();

}

@override

Widget build(BuildContext context) {

if (widget.src == null) {

return const SizedBox.expand();

}

return HtmlElementView(

viewType: ImgElementPlatformView._viewType,

onPlatformViewCreated: _onPlatformViewCreated,

hitTestBehavior: PlatformViewHitTestBehavior.transparent,

);

}

/// A widget which displays and lays out an underlying HTML element in a

/// platform view.

class RawWebImage extends SingleChildRenderObjectWidget {

/// Creates a [RawWebImage].

RawWebImage({

super.key,

required this.image,

this.debugImageLabel,

this.width,

this.height,

this.fit,

this.alignment = Alignment.center,

this.matchTextDirection = false,

}) : super(child: ImgElementPlatformView(image.htmlImage.src));

/// The underlying HTML element to be displayed.

final WebImageInfo image;

/// A debug label explaining the image.

final String? debugImageLabel;

/// The requested width for this widget.

final double? width;

/// The requested height for this widget.

final double? height;

/// How the HTML element should be inscribed in the box constraining it.

final BoxFit? fit;

/// How the image should be aligned in the box constraining it.

final AlignmentGeometry alignment;

/// Whether or not the alignment of the image should match the text direction.

final bool matchTextDirection;

@override

RenderObject createRenderObject(BuildContext context) {

return RenderWebImage(

image: image.htmlImage,

width: width,

height: height,

fit: fit,

alignment: alignment,

matchTextDirection: matchTextDirection,

textDirection: matchTextDirection || alignment is! Alignment

? Directionality.of(context)

: null,

);

}

@override

void updateRenderObject(BuildContext context, RenderWebImage renderObject) {

renderObject

..image = image.htmlImage

..width = width

..height = height

..fit = fit

..alignment = alignment

..matchTextDirection = matchTextDirection

..textDirection = matchTextDirection || alignment is! Alignment

? Directionality.of(context)

: null;

}

/// Lays out and positions the child HTML element similarly to [RenderImage].

class RenderWebImage extends RenderShiftedBox {

/// Creates a new [RenderWebImage].

RenderWebImage({

RenderBox? child,

required this._image,

this._width,

this._height,

this._fit,

this._alignment = Alignment.center,

this._matchTextDirection = false,

this._textDirection,

}) : super(child);

Alignment? _resolvedAlignment;

bool? _flipHorizontally;

bool _needsClip = false;

void _resolve() {

if (_resolvedAlignment != null) {

return;

}

_resolvedAlignment = alignment.resolve(textDirection);

_flipHorizontally = matchTextDirection && textDirection == TextDirection.rtl;

}

void _markNeedResolution() {

_resolvedAlignment = null;

_flipHorizontally = null;

markNeedsLayout();

}

/// Whether to paint the image in the direction of the [TextDirection].

///

/// If this is true, then in [TextDirection.ltr] contexts, the image will be

/// drawn with its origin in the top left (the "normal" painting direction for

/// images); and in [TextDirection.rtl] contexts, the image will be drawn with

/// a scaling factor of -1 in the horizontal direction so that the origin is

/// in the top right.

///

/// This is occasionally used with images in right-to-left environments, for

/// images that were designed for left-to-right locales. Be careful, when

/// using this, to not flip images with integral shadows, text, or other

/// effects that will look incorrect when flipped.

///

/// If this is set to true, [textDirection] must not be null.

bool get matchTextDirection => _matchTextDirection;

bool _matchTextDirection;

set matchTextDirection(bool value) {

if (value == _matchTextDirection) {

return;

}

_matchTextDirection = value;

_markNeedResolution();

}

/// The text direction with which to resolve [alignment].

///

/// This may be changed to null, but only after the [alignment] and

/// [matchTextDirection] properties have been changed to values that do not

/// depend on the direction.

TextDirection? get textDirection => _textDirection;

TextDirection? _textDirection;

set textDirection(TextDirection? value) {

if (_textDirection == value) {

return;

}

_textDirection = value;

_markNeedResolution();

}

/// The image to display.

web.HTMLImageElement get image => _image;

web.HTMLImageElement _image;

set image(web.HTMLImageElement value) {

if (value == _image) {

return;

}

// If we get a clone of our image, it's the same underlying native data -

// return early.

if (value.src == _image.src) {

return;

}

final bool sizeChanged =

_image.naturalWidth != value.naturalWidth || _image.naturalHeight != value.naturalHeight;

_image = value;

markNeedsPaint();

if (sizeChanged && (_width == null || _height == null)) {

markNeedsLayout();

}

/// If non-null, requires the image to have this width.

///

/// If null, the image will pick a size that best preserves its intrinsic

/// aspect ratio.

double? get width => _width;

double? _width;

set width(double? value) {

if (value == _width) {

return;

}

_width = value;

markNeedsLayout();

}

/// If non-null, require the image to have this height.

///

/// If null, the image will pick a size that best preserves its intrinsic

/// aspect ratio.

double? get height => _height;

double? _height;

set height(double? value) {

if (value == _height) {

return;

}

_height = value;

markNeedsLayout();

}

/// How to inscribe the image into the space allocated during layout.

///

/// The default varies based on the other fields. See the discussion at

/// [paintImage].

BoxFit? get fit => _fit;

BoxFit? _fit;

set fit(BoxFit? value) {

if (value == _fit) {

return;

}

_fit = value;

markNeedsLayout();

}

/// How to align the image within its bounds.

///

/// If this is set to a text-direction-dependent value, [textDirection] must

/// not be null.

AlignmentGeometry get alignment => _alignment;

AlignmentGeometry _alignment;

set alignment(AlignmentGeometry value) {

if (value == _alignment) {

return;

}

_alignment = value;

_markNeedResolution();

}

/// Find a size for the render image within the given constraints.

///

/// - The dimensions of the RenderImage must fit within the constraints.

/// - The aspect ratio of the RenderImage matches the intrinsic aspect

/// ratio of the image.

/// - The RenderImage's dimension are maximal subject to being smaller than

/// the intrinsic size of the image.

Size _sizeForConstraints(BoxConstraints constraints) {

// be treated uniformly.

constraints = BoxConstraints.tightFor(width: _width, height: _height).enforce(constraints);

return constraints.constrainSizeAndAttemptToPreserveAspectRatio(

Size(_image.naturalWidth.toDouble(), _image.naturalHeight.toDouble()),

);

}

@override

double computeMinIntrinsicWidth(double height) {

assert(height >= 0.0);

if (_width == null && _height == null) {

return 0.0;

}

return _sizeForConstraints(BoxConstraints.tightForFinite(height: height)).width;

}

@override

double computeMaxIntrinsicWidth(double height) {

assert(height >= 0.0);

return _sizeForConstraints(BoxConstraints.tightForFinite(height: height)).width;

}

@override

double computeMinIntrinsicHeight(double width) {

assert(width >= 0.0);

if (_width == null && _height == null) {

return 0.0;

}

return _sizeForConstraints(BoxConstraints.tightForFinite(width: width)).height;

}

@override

double computeMaxIntrinsicHeight(double width) {

assert(width >= 0.0);

return _sizeForConstraints(BoxConstraints.tightForFinite(width: width)).height;

}

@override

bool hitTestSelf(Offset position) => true;

@override

@protected

Size computeDryLayout(covariant BoxConstraints constraints) {

return _sizeForConstraints(constraints);

}

@override

void performLayout() {

_resolve();

assert(_resolvedAlignment != null);

assert(_flipHorizontally != null);

size = _sizeForConstraints(constraints);

if (child == null) {

return;

}

// Size and position the <img> element child.

// The `ImgElementPlatformView` which contains the `<img>` element is sized

// independently of the `RenderWebImage`. The `RenderWebImage` needs to

// size and position its child to match the `BoxFit` and `Alignment`

// properties.

// The child could be smaller or larger than the `RenderWebImage`. If the

// child is larger, then it will be clipped in the `paint` step.

final inputSize = Size(image.naturalWidth.toDouble(), image.naturalHeight.toDouble());

final BoxFit resolvedFit = fit ?? BoxFit.scaleDown;

final FittedSizes fittedSizes = applyBoxFit(resolvedFit, inputSize, size);

if (fittedSizes.source == inputSize) {

// If `fittedSizes.source` is the entire original image, then the child

// can be sized to `fittedSizes.destination` because there will be no

// clipping and the child will be exactly the destination size.

final Size childSize = fittedSizes.destination;

child!.layout(BoxConstraints.tight(childSize));

// In case the `childSize` is smaller than the layout constraints (for

// example, if the `fit` is `BoxFit.fitWidth` and the resulting child

// size causes it to "letterbox" in the containing box) then the child

// needs to be offset in the containing box.

final double halfWidthDelta = (size.width - childSize.width) / 2.0;

final double halfHeightDelta = (size.height - childSize.height) / 2.0;

final double dx =

halfWidthDelta +

(_flipHorizontally! ? -_resolvedAlignment!.x : _resolvedAlignment!.x) * halfWidthDelta;

final double dy = halfHeightDelta + _resolvedAlignment!.y * halfHeightDelta;

final childParentData = child!.parentData! as BoxParentData;

childParentData.offset = Offset(dx, dy);

_needsClip = false;

} else {

// Otherwise, the destination box only shows a portion of the image and

// the rest of the image overflows out of the box. The size of the child

// needs to be worked out from the size of the source and destination

// boxes. The offset of the child needs to be worked out from the

// alignment. In the `paint` method, a clip will be applied so that only

// the portion of the child that is in the destination box will be shown.

final Size sourceSize = fittedSizes.source;

final Size destinationSize = fittedSizes.destination;

// Only `BoxFit.fill` distorts the aspect ratio of the image. The rest of

// the `BoxFit` values preserve the aspect ratio. Furthermore, if the

// `fit` is `BoxFit.fill` then `fittedSizes.source == inputSize` since the

// entire image is drawn into the box. So the case of `BoxFit.fill` is

// never hit in this branch of the conditional. Therefore, the child

// size should be the source size multiplied by a scalar value. The scale

// can be determined by examining the relative sizes of the `sourceSize`

// and `destinationSize`. Since aspect ratio is preserved, `sourceSize`

// and `destinationSize` must have the same aspect ratio. Therefore, the

// scale to multiply the `inputSize` to get the `childSize` is equal to

// the ratio of the `destinationSize` to the `sourceSize`.

assert(

(sourceSize.aspectRatio - destinationSize.aspectRatio).abs() < precisionErrorTolerance,

);

final double scale = destinationSize.width / sourceSize.width;

final Size childSize = inputSize * scale;

child!.layout(BoxConstraints.tight(childSize));

// Now that the child has been sized, it must also be offset by an

// appropriate amount so that the specified portion of the image is shown

// in the destination box. `Alignment.inscribe` gives the sub-rectangle

// of source size that will be shown in the destination box. Again, the

// source and destination box have the same aspect ratio, so to compute

// the offset for the child, first compute the offset that the original

// sized image would need to put the sub-rectangle given by

// `Alignment.inscribe` at the origin, and then scale that offset by the

// same scale computed above to get the offset for the child.

final Rect sourceRect = _resolvedAlignment!.inscribe(sourceSize, Offset.zero & inputSize);

final Offset childOffset = Offset(-sourceRect.left, -sourceRect.top) * scale;

final childParentData = child!.parentData! as BoxParentData;

childParentData.offset = childOffset;

_needsClip = true;

}

@override

void paint(PaintingContext context, Offset offset) {

if (child == null) {

return;

}

if (_needsClip) {

final Rect destinationRect = Offset.zero & size;

context.pushClipRect(needsCompositing, offset, destinationRect, super.paint);

} else {

super.paint(context, offset);

}

@override

void debugFillProperties(DiagnosticPropertiesBuilder properties) {

super.debugFillProperties(properties);

properties.add(DiagnosticsProperty<web.HTMLImageElement>('image', image));

properties.add(DoubleProperty('width', width, defaultValue: null));

properties.add(DoubleProperty('height', height, defaultValue: null));

properties.add(EnumProperty<BoxFit>('fit', fit, defaultValue: null));

properties.add(

DiagnosticsProperty<AlignmentGeometry>('alignment', alignment, defaultValue: null),

);

}

flutter/packages/flutter/lib/src/widgets/_web_image_web.dart at master · flutter/flutter · GitHub

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