Bug 1599421 - Enforce a minimum size on the Picture-in-Picture player window on Linux GTK. r=mstriemer

macOS and Windows seem to already have minimum window size limits that
make sense, so this hacks in a minimum size just for Linux GTK and leaves
the others alone.

Differential Revision: https://phabricator.services.mozilla.com/D55152

--HG--
extra : moz-landing-system : lando

toolkit/components/pictureinpicture/content/player.js

@@ -9,6 +9,9 @@ const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
 const { DeferredTask } = ChromeUtils.import(
   "resource://gre/modules/DeferredTask.jsm"
 );
+const { AppConstants } = ChromeUtils.import(
+  "resource://gre/modules/AppConstants.jsm"
+);
 
 const AUDIO_TOGGLE_ENABLED_PREF =
   "media.videocontrols.picture-in-picture.audio-toggle.enabled";
@@ -144,6 +147,8 @@ let Player = {
       screenX: window.screenX.toString(),
       screenY: window.screenY.toString(),
     });
+
+    this.computeAndSetMinimumSize(window.outerWidth, window.outerHeight);
   },
 
   uninit() {
@@ -323,4 +328,46 @@ let Player = {
       }, CONTROLS_FADE_TIMEOUT_MS);
     }
   },
+
+  /**
+   * Given a width and height for a video, computes the minimum dimensions for
+   * the player window, and then sets them on the root element.
+   *
+   * This is currently only used on Linux GTK, where the OS doesn't already
+   * impose a minimum window size. For other platforms, this function is a
+   * no-op.
+   *
+   * @param width (Number)
+   *   The width of the video being played.
+   * @param height (Number)
+   *   The height of the video being played.
+   */
+  computeAndSetMinimumSize(width, height) {
+    if (!AppConstants.MOZ_WIDGET_GTK) {
+      return;
+    }
+
+    // Using inspection, these seem to be the right minimums for each dimension
+    // so that the controls don't get too crowded.
+    const MIN_WIDTH = 120;
+    const MIN_HEIGHT = 80;
+
+    let resultWidth = width;
+    let resultHeight = height;
+    let aspectRatio = width / height;
+
+    // Take the smaller of the two dimensions, and set it to the minimum.
+    // Then calculate the other dimension using the aspect ratio to get
+    // both minimums.
+    if (width < height) {
+      resultWidth = MIN_WIDTH;
+      resultHeight = Math.round(MIN_WIDTH / aspectRatio);
+    } else {
+      resultHeight = MIN_HEIGHT;
+      resultWidth = Math.round(MIN_HEIGHT * aspectRatio);
+    }
+
+    document.documentElement.style.minWidth = resultWidth + "px";
+    document.documentElement.style.minHeight = resultHeight + "px";
+  },
 };