Fix lightbox image transition

src/components/Lightbox.vue

@@ -38,6 +38,7 @@ export default {
 			gMouseDownOffsetX: 0,
 			gMouseDownOffsetY: 0,
 			resizeTimer: null,
+			mediaLoadId: 0,
 			containerPadding: null,
 			imageBorderWidth: null,
 			videoBorderWidth: null,
@@ -93,7 +94,6 @@ export default {
 	},
 	methods: {
 		open(album, startId, source) {
-			this.sizeOverlay();
 			this.album = album.map((options) => this.mapMedia(options, source));
 			const startIndex = Math.max(this.album.findIndex((media) => media.id == startId), 0);
 
@@ -106,6 +106,7 @@ export default {
 			this.changeImage(startIndex);
 		},
 		end(dispose = false) {
+			this.mediaLoadId++; //Drop any pending image/video load
 			this.disableKeyboardNav();
 			this.$refs.video?.pause();
 			this.$refs.video?.removeAttribute('src');
@@ -242,6 +243,7 @@ export default {
 		changeImage(index) {
 			const media = this.album[index];
 			if(!media) return;
+			const loadId = ++this.mediaLoadId;
 
 			this.updateDetails(media, false);
 			this.hideElements([this.$refs.dataContainer]);
@@ -260,6 +262,7 @@ export default {
 				this.$refs.image.removeAttribute('src');
 				this.$refs.container.classList.add('lb-video-nav');
 				this.$refs.video.onloadedmetadata = () => {
+					if(loadId !== this.mediaLoadId) return;
 					media.width = this.$refs.video.videoWidth;
 					media.height = this.$refs.video.videoHeight;
 					this.$refs.video.onloadedmetadata = null;
@@ -269,10 +272,15 @@ export default {
 			} else {
 				this.$refs.video.pause();
 				this.$refs.video.removeAttribute('src');
-				this.$refs.image.onload = () => {
-					this.$refs.image.alt = media.alt;
-					let width = this.$refs.image.naturalWidth;
-					let height = this.$refs.image.naturalHeight;
+				//Load & decode in a detached image, so that neither the placeholder nor the previous picture can be measured or painted
+				const loader = new Image();
+				loader.src = media.link;
+				loader.decode().then(() => {
+					//A previous request may still resolve after a new one started: only the latest one counts
+					if(loadId !== this.mediaLoadId) return;
+
+					let width = loader.naturalWidth;
+					let height = loader.naturalHeight;
 					if(Math.abs(media.orientation) === 90 && width > height) {
 						const tmp = width;
 						width = height;
@@ -280,10 +288,12 @@ export default {
 					}
 					media.width = width;
 					media.height = height;
-					this.$refs.image.onload = null;
-					this.updateSize(index);
-				};
+					this.$refs.image.alt = media.alt;
 					this.$refs.image.src = media.link;
+					this.updateSize(index);
+				}).catch((error) => {
+					if(loadId === this.mediaLoadId) console.error('Lightbox: unable to load image', media.link, error);
+				});
 			}
 		},
 		sizeOverlay() {