src: Allow windows to be transparent, behind a pref (off by default)

Add a `core.allowWindowTransparency` pref (off by default).

Sets `options.transparent = true` for the `browserWindow` `options`
when this pref is enabled.

Requires a restart to activate.

Co-credit to savetheclocktower for the revised description of the pref.

Co-authored-by: Andrew Dupont <github@andrewdupont.net>

src/config-schema.js

@@ -399,6 +399,12 @@ const configSchema = {
         description: 'Add the current tab title to the Pulsar Window title.',
         type: 'boolean',
         default: true
+      },
+      allowWindowTransparency: {
+        type: 'boolean',
+        default: false,
+        title: 'Allow Window Transparency',
+        description: `Allows editor windows to be see-through. When this setting is enabled, UI themes and user stylesheets can use background colors with an alpha channel to make editor windows translucent. Takes effect after a restart of Pulsar.`
       }
     }
   },

src/main-process/atom-application.js

@@ -285,6 +285,9 @@ module.exports = class AtomApplication extends EventEmitter {
         this.config.onDidChange('core.colorProfile', () =>
           this.promptForRestart()
         );
+        this.config.onDidChange('core.allowWindowTransparency', () =>
+          this.promptForRestart()
+        );
       });
       await this.configFilePromise;
     }

src/main-process/atom-window.js

@@ -80,6 +80,10 @@ module.exports = class AtomWindow extends EventEmitter {
       options.titleBarStyle = 'hiddenInset';
     if (this.shouldHideTitleBar()) options.frame = false;
 
+    if(this.atomApplication.config.get('core.allowWindowTransparency')){
+      options.transparent = true;
+    }
+
     const BrowserWindowConstructor =
       settings.browserWindowConstructor || BrowserWindow;
     this.browserWindow = new BrowserWindowConstructor(options);