Allow scrollable widget to bind scroll position to a tiddler (#7649)

* Initial Commit

* Update version number

core/modules/widgets/scrollable.js

@@ -171,6 +171,42 @@ ScrollableWidget.prototype.render = function(parent,nextSibling) {
 	parent.insertBefore(this.outerDomNode,nextSibling);
 	this.renderChildren(this.innerDomNode,null);
 	this.domNodes.push(this.outerDomNode);
+	// If the scroll position is bound to a tiddler
+	if(this.scrollableBind) {
+		// After a delay for rendering, scroll to the bound position
+		setTimeout(this.updateScrollPositionFromBoundTiddler.bind(this),50);
+		// Save scroll position on DOM scroll event
+		this.outerDomNode.addEventListener("scroll",function(event) {
+			var existingTiddler = self.wiki.getTiddler(self.scrollableBind),
+				newTiddlerFields = {
+					title: self.scrollableBind,
+					"scroll-left": self.outerDomNode.scrollLeft.toString(),
+					"scroll-top": self.outerDomNode.scrollTop.toString()
+				};
+			if(!existingTiddler || (existingTiddler.fields["scroll-left"] !== newTiddlerFields["scroll-left"] || existingTiddler.fields["scroll-top"] !== newTiddlerFields["scroll-top"])) {
+				self.wiki.addTiddler(new $tw.Tiddler(existingTiddler,newTiddlerFields));
+			}
+		});
+	}
+};
+
+ScrollableWidget.prototype.updateScrollPositionFromBoundTiddler = function() {
+	var tiddler = this.wiki.getTiddler(this.scrollableBind);
+	if(tiddler) {
+		var scrollLeftTo = this.outerDomNode.scrollLeft;
+		if(parseFloat(tiddler.fields["scroll-left"]).toString() === tiddler.fields["scroll-left"]) {
+			scrollLeftTo = parseFloat(tiddler.fields["scroll-left"]);
+		}
+		var scrollTopTo = this.outerDomNode.scrollTop;
+		if(parseFloat(tiddler.fields["scroll-top"]).toString() === tiddler.fields["scroll-top"]) {
+			scrollTopTo = parseFloat(tiddler.fields["scroll-top"]);
+		}
+		this.outerDomNode.scrollTo({
+			top: scrollTopTo,
+			left: scrollLeftTo,
+			behavior: "instant"
+		})
+	}
 };
 
 /*
@@ -178,6 +214,7 @@ Compute the internal state of the widget
 */
 ScrollableWidget.prototype.execute = function() {
 	// Get attributes
+	this.scrollableBind = this.getAttribute("bind");
 	this.fallthrough = this.getAttribute("fallthrough","yes");
 	this["class"] = this.getAttribute("class");
 	// Make child widgets
@@ -193,6 +230,9 @@ ScrollableWidget.prototype.refresh = function(changedTiddlers) {
 		this.refreshSelf();
 		return true;
 	}
+	if(changedAttributes.bind || changedTiddlers[this.getAttribute("bind")]) {
+		this.updateScrollPositionFromBoundTiddler();
+	}
 	return this.refreshChildren(changedTiddlers);
 };
 

editions/prerelease/tiddlers/system/temp-my-scroll-position.tid

@@ -0,0 +1,3 @@
+title: $:/my-scroll-position
+scroll-left: 0
+scroll-top: 100

editions/tw5.com/tiddlers/widgets/ScrollableWidget.tid

@@ -1,6 +1,6 @@
 caption: scrollable
 created: 20140324223413403
-modified: 20220620115347910
+modified: 20230731100903977
 tags: Widgets
 title: ScrollableWidget
 type: text/vnd.tiddlywiki
@@ -16,12 +16,15 @@ The content of the `<$scrollable>` widget is displayed within a pair of wrapper
 |!Attribute |!Description |
 |class |The CSS class(es) to be applied to the outer DIV |
 |fallthrough |See below |
+|bind |<<.from-version "5.3.2">> Optional title of tiddler to which the scroll position should be bound |
+
+Binding the scroll position to a tiddler automatically copies the scroll coordinates into the `scroll-left` and `scroll-top` fields as scrolling occurs. Conversely, setting those field values will automatically cause the scrollable to scroll if it can.
 
 <$macrocall $name=".note" _="""If a scrollable widget can't handle the `tm-scroll` message because the inner DIV fits within the outer DIV, then by default the message falls through to the parent widget. Setting the ''fallthrough'' attribute to `no` prevents this behaviour."""/> 
 
 ! Examples
 
-This example requires the following CSS definitions from [[$:/_tw5.com-styles]]:
+These examples require the following CSS definitions from [[$:/_tw5.com-styles]]:
 
 ```
 .tc-scrollable-demo {
@@ -33,6 +36,8 @@ This example requires the following CSS definitions from [[$:/_tw5.com-styles]]:
 }
 ```
 
+!! Simple Usage
+
 This wiki text shows how to display a list within the scrollable widget:
 
 <<wikitext-example-without-html "<$scrollable class='tc-scrollable-demo'>
@@ -46,3 +51,23 @@ This wiki text shows how to display a list within the scrollable widget:
 </$scrollable>
 ">>
 
+!! Binding scroll position to a tiddler
+
+[[Current scroll position|$:/my-scroll-position]]: {{$:/my-scroll-position!!scroll-left}}, {{$:/my-scroll-position!!scroll-top}}
+
+<$button>
+<$action-setfield $tiddler="$:/my-scroll-position" scroll-left="100" scroll-top="100"/>
+Set current scroll position to 100,100
+</$button>
+
+<<wikitext-example-without-html "<$scrollable class='tc-scrollable-demo' bind='$:/my-scroll-position'>
+<$list filter='[tag[Reference]]'>
+
+<$view field='title'/>: <$list filter='[all[current]links[]sort[title]]' storyview='pop'>
+<$link><$view field='title'/></$link>
+</$list>
+
+</$list>
+</$scrollable>
+">>
+