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Fix accessibility issues with image widget #50

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merged 5 commits into from
Apr 8, 2017
Merged

Fix accessibility issues with image widget #50

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440ae11
Include alt text in widget preview
westonruter Apr 6, 2017
e54d54b
Remove alt attribute from widget preview when empty so filename can b…
westonruter Apr 6, 2017
b4146ab
Add describedBy when alt is empty
westonruter Apr 6, 2017
c19a07b
Eliminate needless persistently-hidden not-selected placeholder after…
westonruter Apr 6, 2017
e018842
Merge branch 'master' of https://github.com/xwp/wp-core-media-widgets…
westonruter Apr 6, 2017
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7 changes: 5 additions & 2 deletions wp-admin/js/widgets/media-image-widget.js
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Expand Up @@ -31,9 +31,12 @@
*/
renderPreview: function renderPreview() {
var control = this, previewContainer, previewTemplate;
previewContainer = control.$el.find( '.media-widget-preview .rendered' );
previewContainer = control.$el.find( '.media-widget-preview' );
previewTemplate = wp.template( 'wp-media-widget-image-preview' );
previewContainer.html( previewTemplate( { attachment: control.selectedAttachment.attributes } ) );
previewContainer.html( previewTemplate( _.extend(
control.model.toJSON(),
{ attachment: control.selectedAttachment.toJSON() }
) ) );
},

/**
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4 changes: 3 additions & 1 deletion wp-admin/js/widgets/media-widgets.js
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Expand Up @@ -111,7 +111,9 @@ wp.mediaWidgets = ( function( $ ) {

// Re-render the preview when the attachment changes.
control.selectedAttachment = new wp.media.model.Attachment( { id: 0 } );
control.renderPreview = _.debounce( control.renderPreview );
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I believe, though I could be wrong, that renderPreview is only called when the media modal is closed when the 'Update' button is clicked... if the dialog is closed with the 'x' or hitting the escape key, the model is not updated and renderPreview is not called. So not sure if we need to debounce this or not...

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The reason I added the debounce is because the preview is also now re-rendering in due to changes to control.model. So when you change the media, it will result the model being changed (the attachment_id and url props) as well as the selectedAttachment model, resulting in renderPreview being called twice. So this was intended to be a minor DOM performance improvement to not waste cycles.

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Gotcha, so this saves one render in instances where you are changing media/url. Looks like the preview is rendered twice upon initial load as well when the model is being updated. While playing with this I noticed renderPreview is called on each keystroke when editing the widget title currently so perhaps that is a good candidate for a _.throttle if we are concerned about too many renders.

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The preview rendering is separate. It actually already has throttling via the Customizer in two places. If you type quickly you'll note that the preview doesn't update until you slow down. Debouncing the updates to the widget instance settings is currently handled here: https://github.com/WordPress/wordpress-develop/blob/4.7.3/src/wp-admin/js/customize-widgets.js#L887-L889

The selective refresh of the widget in the preview also gets debounced here: https://github.com/WordPress/wordpress-develop/blob/4.7.3/src/wp-includes/js/customize-selective-refresh.js#L684-L712

And full refreshes are debounced here: https://github.com/WordPress/wordpress-develop/blob/4.7.3/src/wp-admin/js/customize-controls.js#L3655-L3677

For the core fix to reduce the number of preview refreshes in rapid succession, such as with implementing a decay, see https://core.trac.wordpress.org/ticket/38954

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@timmyc timmyc Apr 6, 2017 •
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Great stuff, thanks for those links... so much to learn here. So here is the renderPreview bit in action in the widget itself. I've hacked the alt attribute in the renderPreview method to show how many times it is called. Note that the number increments with each keystroke of the title which is triggering the change on control.model. This is happening in master here too, mis-spoke there, it is the addition of control.listenTo( control.model, 'change', control.renderPreview ); that causes the preview to re-render whenever the title changes.

refresh

control.listenTo( control.selectedAttachment, 'change', control.renderPreview );
control.listenTo( control.model, 'change', control.renderPreview );

// Make sure a copy of the selected attachment is always fetched.
control.model.on( 'change', control.fetchSelectedAttachment );
Expand Down Expand Up @@ -370,7 +372,7 @@ wp.mediaWidgets = ( function( $ ) {
var control = this, titleInput;

if ( ! control.templateRendered ) {
control.$el.html( control.template()( control.model.attributes ) );
control.$el.html( control.template()( control.model.toJSON() ) );
control.renderPreview(); // Hereafter it will re-render when control.selectedAttachment changes.
control.templateRendered = true;
}
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22 changes: 20 additions & 2 deletions wp-includes/widgets/class-wp-widget-image.php
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Expand Up @@ -284,6 +284,9 @@ public function render_control_template_scripts() {

?>
<script type="text/html" id="tmpl-wp-media-widget-image-preview">
<#
var describedById = 'describedBy-' + String( Math.random() );
#>
<# if ( data.attachment.error && 'missing_attachment' === data.attachment.error ) { #>
<div class="notice notice-error notice-alt notice-missing-attachment">
<p><?php echo $this->l10n['missing_attachment']; ?></p>
Expand All @@ -292,8 +295,23 @@ public function render_control_template_scripts() {
<div class="notice notice-error notice-alt">
<p><?php _e( 'Unable to preview media due to an unknown error.' ); ?></p>
</div>
<# } else if ( data.attachment.url ) { #>
<img class="attachment-thumb" src="{{ data.attachment.url }}" draggable="false" alt="" />
<# } else if ( data.attachment.url || data.url ) { #>
<img class="attachment-thumb" src="{{ data.attachment.url || data.url }}" draggable="false" alt="{{ data.alt }}" <# if ( ! data.alt ) { #> aria-describedby="{{ describedById }}" <# } #> />
<# if ( ! data.alt ) { #>
<#
var alt = ( data.attachment.url || data.url );
alt = alt.replace( /\?.*$/, '' );
alt = alt.replace( /^.+\//, '' );
#>
<p class="hidden" id="{{ describedById }}"><?php
/* translators: placeholder is image filename */
echo sprintf( __( 'Current image: %s' ), '{{ alt }}' );
?></p>
<# } #>
<# } else { #>
<div class="attachment-media-view">
<p class="placeholder"><?php echo esc_html( $this->l10n['no_media_selected'] ); ?></p>
</div>
<# } #>
</script>
<?php
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5 changes: 1 addition & 4 deletions wp-includes/widgets/class-wp-widget-media.php
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Expand Up @@ -341,10 +341,7 @@ public function render_control_template_scripts() {
<input id="{{ elementIdPrefix }}title" type="text" class="widefat title">
</p>
<div class="media-widget-preview">
<div class="selected rendered">
<!-- Media rendering goes here. -->
</div>
<div class="attachment-media-view not-selected">
<div class="attachment-media-view">
<p class="placeholder"><?php echo esc_html( $this->l10n['no_media_selected'] ); ?></p>
</div>
</div>
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