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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,107 @@ | ||
| /** | ||
| * @fileoverview This script handles zooming and panning functionality for an image within a container. | ||
| * It can be used as an -- admittedly hacky -- workaround to run custom JavaScript logic in Dash apps, | ||
| * including script that needs to run in response to an app.callback update. | ||
| * | ||
| * The `custom_js_trigger` element is used for communicating to the script from Dash updates that custom JS logic has to be run. | ||
| * When running an app.callback, the `title` attribute of `custom_js_trigger` can be updated (`Output("custom_js_trigger", "title")`) to trigger specific JS code. | ||
| * The mutation on the elements `custom_js_trigger` are observed to detect changes in the `data-dash-is-loading` attribute, which is set by Dash when an element is loading. | ||
| * The specific code that needs to run is determined by the value of the `title` attribute of the `custom_js_trigger` element. | ||
| * | ||
| * Because Dash is slow to add elements to the page as a result of API calls, | ||
| * the script s `waitForElement()` to wait for specific elements to be available in the DOM before attaching event listeners or running other logic on the element. | ||
| * (The DOMContentLoaded event is not sufficient because some elements load faster than others). | ||
| * | ||
| * JS packages can be loaded from CDN in main.py using the `external_scripts` argument of the app object. | ||
| */ | ||
|
|
||
| /** | ||
| * Custom JS logic | ||
| */ | ||
|
|
||
| // Script-wide variables used to communicate between scripts that await different elements to load. | ||
| let switching_to_other_alert = false; | ||
| let panzoomInstance = null; | ||
|
|
||
| // Utility function to waits for an element to be available in the DOM before running JS code that depends on the element. | ||
| function waitForElement(selector) { | ||
| return new Promise((resolve) => { | ||
| if (document.querySelector(selector)) { | ||
| return resolve(document.querySelector(selector)); | ||
| } | ||
|
|
||
| const observer = new MutationObserver((mutations) => { | ||
| if (document.querySelector(selector)) { | ||
| observer.disconnect(); | ||
| resolve(document.querySelector(selector)); | ||
| } | ||
| }); | ||
|
|
||
| observer.observe(document.body, { | ||
| childList: true, | ||
| subtree: true, | ||
| }); | ||
| }); | ||
| } | ||
|
|
||
| // Observe mutations of the `custom_js_trigger` element to detect changes in the `data-dash-is-loading` and trigger custon JS as a response. | ||
| waitForElement("#custom_js_trigger").then((trigger) => { | ||
| const observer = new MutationObserver((mutations) => { | ||
| mutations.forEach((mutation) => { | ||
| if ( | ||
| mutation.type === "attributes" && | ||
| mutation.attributeName === "data-dash-is-loading" | ||
| ) { | ||
| if (trigger.title == "reset_zoom") { | ||
| switching_to_other_alert = true; | ||
| } | ||
| } | ||
| }); | ||
| }); | ||
|
|
||
| observer.observe(trigger, { | ||
| attributes: true, | ||
| }); | ||
| }); | ||
|
|
||
| /** | ||
| * Custom JS scripts | ||
| */ | ||
|
|
||
| // Initializes the Panzoom instance on the container and adjusts the bounding box styling on transform. | ||
| waitForElement("#image-container-with-bbox").then((container) => { | ||
| panzoomInstance = panzoom(container, { | ||
| bounds: true, | ||
| boundsPadding: 1, | ||
| minZoom: 1, | ||
| initialX: 0, | ||
| initialY: 0, | ||
| initialZoom: 1, | ||
| }); | ||
|
|
||
| panzoomInstance.on("transform", (e) => { | ||
| const transform = panzoomInstance.getTransform(); | ||
|
|
||
| const bbox = document.querySelector("#bbox-styling"); | ||
| if (bbox) { | ||
| const newThickness = 2 / transform.scale; | ||
| bbox.style.border = `${newThickness}px solid red`; | ||
| } | ||
|
|
||
| if (transform.scale === 1) { | ||
| container.style.transform = ""; | ||
| } | ||
| }); | ||
|
|
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| // Resets the zoom level when the main image is loaded. | ||
| waitForElement("#main-image").then((image) => { | ||
| image.onload = () => { | ||
| // Waiting for image to load avoids flicker whereby old image is zoomed out before new image is loaded | ||
| if (switching_to_other_alert) { | ||
| switching_to_other_alert = false; | ||
| panzoomInstance.moveTo(0, 0); | ||
| panzoomInstance.zoomAbs(0, 0, 1); | ||
| } | ||
| }; | ||
| }); | ||
| }); |
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