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Merge pull request #3399 from pattch/master
Add a Time-Based Debouncer to update Screen Readers at most once per second
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/** | ||
* Copyright (c) 2018 The xterm.js authors. All rights reserved. | ||
* @license MIT | ||
*/ | ||
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const RENDER_DEBOUNCE_THRESHOLD_MS = 1000; // 1 Second | ||
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import { IRenderDebouncer } from 'browser/Types'; | ||
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/** | ||
* Debounces calls to update screen readers to update at most once configurable interval of time. | ||
*/ | ||
export class TimeBasedDebouncer implements IRenderDebouncer { | ||
private _rowStart: number | undefined; | ||
private _rowEnd: number | undefined; | ||
private _rowCount: number | undefined; | ||
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// The last moment that the Terminal was refreshed at | ||
private _lastRefreshMs = 0; | ||
// Whether a trailing refresh should be triggered due to a refresh request that was throttled | ||
private _additionalRefreshRequested = false; | ||
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private _refreshTimeoutID: number | undefined; | ||
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constructor( | ||
private _renderCallback: (start: number, end: number) => void, | ||
private readonly _debounceThresholdMS = RENDER_DEBOUNCE_THRESHOLD_MS | ||
) { | ||
} | ||
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public dispose(): void { | ||
if (this._refreshTimeoutID) { | ||
clearTimeout(this._refreshTimeoutID); | ||
} | ||
} | ||
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public refresh(rowStart: number | undefined, rowEnd: number | undefined, rowCount: number): void { | ||
this._rowCount = rowCount; | ||
// Get the min/max row start/end for the arg values | ||
rowStart = rowStart !== undefined ? rowStart : 0; | ||
rowEnd = rowEnd !== undefined ? rowEnd : this._rowCount - 1; | ||
// Set the properties to the updated values | ||
this._rowStart = this._rowStart !== undefined ? Math.min(this._rowStart, rowStart) : rowStart; | ||
this._rowEnd = this._rowEnd !== undefined ? Math.max(this._rowEnd, rowEnd) : rowEnd; | ||
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// Only refresh if the time since last refresh is above a threshold, otherwise wait for | ||
// enough time to pass before refreshing again. | ||
const refreshRequestTime: number = Date.now(); | ||
if (refreshRequestTime - this._lastRefreshMs >= this._debounceThresholdMS) { | ||
// Enough time has lapsed since the last refresh; refresh immediately | ||
this._lastRefreshMs = refreshRequestTime; | ||
this._innerRefresh(); | ||
} else if (!this._additionalRefreshRequested) { | ||
// This is the first additional request throttled; set up trailing refresh | ||
const elapsed = refreshRequestTime - this._lastRefreshMs; | ||
const waitPeriodBeforeTrailingRefresh = this._debounceThresholdMS - elapsed; | ||
this._additionalRefreshRequested = true; | ||
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this._refreshTimeoutID = window.setTimeout(() => { | ||
this._lastRefreshMs = Date.now(); | ||
this._innerRefresh(); | ||
this._additionalRefreshRequested = false; | ||
this._refreshTimeoutID = undefined; // No longer need to clear the timeout | ||
}, waitPeriodBeforeTrailingRefresh); | ||
} | ||
} | ||
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private _innerRefresh(): void { | ||
// Make sure values are set | ||
if (this._rowStart === undefined || this._rowEnd === undefined || this._rowCount === undefined) { | ||
return; | ||
} | ||
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// Clamp values | ||
const start = Math.max(this._rowStart, 0); | ||
const end = Math.min(this._rowEnd, this._rowCount - 1); | ||
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// Reset debouncer (this happens before render callback as the render could trigger it again) | ||
this._rowStart = undefined; | ||
this._rowEnd = undefined; | ||
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// Run render callback | ||
this._renderCallback(start, end); | ||
} | ||
} | ||
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