Remove ghost from crossfade during scroll

Fixes: sveltejs#4111

Author: sheijne

src/runtime/transition/index.ts

@@ -204,21 +204,22 @@ interface CrossfadeParams {
 	easing: EasingFunction;
 }
 
-type ClientRectMap = Map<any, { rect: ClientRect }>;
+type ElementMap = Map<any, { node: Element }>;
 
 export function crossfade({ fallback, ...defaults }: CrossfadeParams & {
 	fallback: (node: Element, params: CrossfadeParams, intro: boolean) => TransitionConfig;
 }) {
-	const to_receive: ClientRectMap = new Map();
-	const to_send: ClientRectMap = new Map();
+	const to_receive: ElementMap = new Map();
+	const to_send: ElementMap = new Map();
 
-	function crossfade(from: ClientRect, node: Element, params: CrossfadeParams): TransitionConfig {
+	function crossfade(from_node: Element, node: Element, params: CrossfadeParams): TransitionConfig {
 		const {
 			delay = 0,
 			duration = d => Math.sqrt(d) * 30,
 			easing = cubicOut
 		} = assign(assign({}, defaults), params);
 
+        const from = from_node.getBoundingClientRect();
 		const to = node.getBoundingClientRect();
 		const dx = from.left - to.left;
 		const dy = from.top - to.top;
@@ -242,18 +243,16 @@ export function crossfade({ fallback, ...defaults }: CrossfadeParams & {
 		};
 	}
 
-	function transition(items: ClientRectMap, counterparts: ClientRectMap, intro: boolean) {
+	function transition(items: ElementMap, counterparts: ElementMap, intro: boolean) {
 		return (node: Element, params: CrossfadeParams & { key: any }) => {
-			items.set(params.key, {
-				rect: node.getBoundingClientRect()
-			});
+			items.set(params.key, { node });
 
 			return () => {
 				if (counterparts.has(params.key)) {
-					const { rect } = counterparts.get(params.key);
+					const from_node = counterparts.get(params.key).node;
 					counterparts.delete(params.key);
 
-					return crossfade(rect, node, params);
+					return crossfade(from_node, node, params);
 				}
 
 				// if the node is disappearing altogether