UI Data & State

The Surface component provides save and load methods that allow you to persist and restore the entire state of your canvas, including the underlying data model, the UI's pan/zoom state, and the state of any registered plugins/components, such as the Inspector. You'll need to access the surface to use these methods programmatically - expand the section below for details.

How to access the surface

From your app component

To access the surface from inside a component that uses a SurfaceComponent, declare a ref of type SurfaceComponent and assign it in the template.

You can then access the model through the ref's value, which is of type SurfaceComponent

<script setup lang="ts">
import { SurfaceComponent} from "@visuallyjs/browser-ui-svelte"

let surfaceComponent: SurfaceComponent = $state(null)
    
function centerContent() {
	surfaceComponent.getSurface().centerContent()
}
</script>
<template>
  <SurfaceComponent  bind:this={surfaceComponent}/>
  <button onClick={() => centerContent()}>Center Content!</button>
</template>

From a different component

If you have a component somewhere in your tree from which you wish to interact with the surface, you can use the useSurface() hook in conjunction with a SurfaceProvider to access the surface. Your app component should look something like this:

<script setup lang="ts">
</script>
<template>
  <SurfaceProvider>
    <SurfaceComponent/>
    <MyOtherComponent/>
  </SurfaceProvider>
</template>

Then the implementation of MyOtherComponent can use the useSurface hook:

<script setup lang="ts">

  import { useSurface } from "@visuallyjs/browser-ui-svelte"
  import { Surface } from "@visuallyjs/browser-ui"
    
  const surface:RefObject<Surface> = useSurface() // this is reactive state

  function centerContent() {
    surface.current.centerContent()
  }
    
</script>
<template>
  <div><button onClick={() => centerContent()}>Center content!</button></div>
</template>

Saving data & state

The save method is used to capture a complete snapshot of the current Surface state. It returns a JSON object (conforming to the SurfaceSaveData interface) containing:

• Graph Data: The full dataset of all nodes, groups, edges, and ports that have been loaded into the underlying model.
• UI State: The current pan and zoom configuration of the Surface viewport, including the pan position (x, y) and the zoom transform origin. This ensures that the visual position of the canvas is preserved.
• Plugin/Component State: The state of any plugins or components that have registered a data hook. Out of the box, the Inspector component uses this capability, savings its context (such as recently used colors) in the saved data under the inspectorContext key.

// Example of saving the surface state
const currentState = surface.save();

// The `currentState` object now holds the complete snapshot.
// This can be serialized to JSON and stored.
const jsonState = JSON.stringify(currentState);

SurfaceSaveData

Definition of the payload returned from the Surface's save method.

Name	Type	Description
data	any	Data exported from the model
pan	PointXY	The current pan position of the surface canvas
transformOrigin	PointXY	The current position of the surface's transform origin.
zoom	number	The current zoom level

Loading data & state

The load method is the counterpart to save(). It takes a state object (of type SurfaceSaveData) and uses it to restore the Surface to a previously saved state. The load method restores:

• Graph Data: It clears the current model and loads the graph data from the provided state object.
• UI State: After the data is loaded, it restores the pan and zoom of the Surface viewport to their saved values.
• Plugin/Component State: The data is then passed to each of the registered data hooks, which may load their own data and take action as necessary.

// Example of loading a saved state
const savedJsonState = getMySavedState(); // retrieve the stored JSON string
const stateToLoad = JSON.parse(savedJsonState);

surface.load(stateToLoad, () => {
    console.log("Surface has been restored to its previous state.");
});

Data Hooks

The save/load mechanism is extensible, allowing you to include custom data from your own components in the process. This is achieved through the Surface's registerDataHook method. If you have a custom component that manages its own state and you want this state to be persisted along with the rest of the diagram, you can call this method on a surface and register your interest in adding data to the saved data and of loading data from a newly loaded dataset.

The Inspector uses this mechanism out of the box - this is the code:

this.$ui.registerDataHook({
    load:(d:SurfaceSaveData) => {
        // extract inspector context from the load data
        const c = d["inspectorContext"]
        // inspector-specific code...your code will be different
        if (c != null && c.recentColors != null) {
            this.updateContext(INSPECTOR_CONTEXT_RECENT_COLORS, c.recentColors.slice())
        }
    },
    save:(d:SurfaceSaveData) => {
        // store the inspector context on the save data
        d["inspectorContext"] = Object.assign({}, this.$context)
    }
})