Use a more robust solution to changing devicePixelRatio

2017-12-29 13:54:01 -08:00
parent ef5beb6706
commit 72d946e089
3 changed files with 67 additions and 5 deletions
@@ -0,0 +1,62 @@
+/**
+ * Copyright (c) 2017 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+export type ScreenDprListener = (newDevicePixelRatio?: number, oldDevicePixelRatio?: number) => void;
+
+/**
+ * The screen device pixel ratio monitor allows listening for when the
+ * window.devicePixelRatio value changes. This is done not with polling but with
+ * the use of window.matchMedia to watch media queries. When the event fires,
+ * the listener will be reattached using a different media query to ensure that
+ * any further changes will register.
+ *
+ * The listener should fire on both window zoom changes and switching to a
+ * monitor with a different DPI.
+ */
+export class ScreenDprMonitor {
+  private _currentDevicePixelRatio: number;
+  private _outerListener: MediaQueryListListener;
+  private _listener: ScreenDprListener;
+  private _minMediaMatchList: MediaQueryList;
+  private _maxMediaMatchList: MediaQueryList;
+
+  public setListener(listener: ScreenDprListener): void {
+    if (this._listener) {
+      this.clearListener();
+    }
+    this._listener = listener;
+    this._outerListener = () => {
+      this._listener(window.devicePixelRatio, this._currentDevicePixelRatio);
+      this._updateDpr();
+    };
+    this._updateDpr();
+  }
+
+  private _updateDpr(): void {
+    // Clear listeners for old DPR
+    if (this._minMediaMatchList) {
+      this._minMediaMatchList.removeListener(this._outerListener);
+    }
+    if (this._maxMediaMatchList) {
+      this._maxMediaMatchList.removeListener(this._outerListener);
+    }
+    // Add listeners for new DPR
+    this._currentDevicePixelRatio = window.devicePixelRatio;
+    this._minMediaMatchList = window.matchMedia(`screen and (-webkit-min-device-pixel-ratio: ${window.devicePixelRatio})`);
+    this._maxMediaMatchList = window.matchMedia(`screen and (-webkit-max-device-pixel-ratio: ${window.devicePixelRatio})`);
+    this._minMediaMatchList.addListener(this._outerListener);
+    this._maxMediaMatchList.addListener(this._outerListener);
+  }
+
+  public clearListener(): void {
+    if (!this._listener) {
+      return;
+    }
+    this._minMediaMatchList.removeListener(this._outerListener);
+    this._maxMediaMatchList.removeListener(this._outerListener);
+    this._listener = null;
+    this._outerListener = null;
+  }
+}