Prevent electron flashing white screen on startup (#3001)

see #1919

thanks @dfanica for providing the solution in [this
comment](#1919 (comment))

tested this on a pi4 with bullseye 32-bit and 64-bit

CHANGELOG.md

@@ -35,6 +35,7 @@ _This release is scheduled to be released on 2023-04-01._
 
 - Fix wrong day labels in envcanada forecast (#2987)
 - Fix for missing default class name prefix for customEvents in calendar
+- Fixed electron flashing white screen on startup (#1919)
 - Fix weathergov provider hourly forecast (#3008)
 - Fix message display with HTML code into alert module (#2828)
 - Fix typo into french translation

js/electron.js

@@ -46,8 +46,10 @@ function createWindow() {
 	if (config.kioskmode) {
 		electronOptionsDefaults.kiosk = true;
 	} else {
-		electronOptionsDefaults.fullscreen = true;
-		electronOptionsDefaults.autoHideMenuBar = true;
+		electronOptionsDefaults.show = false;
+		electronOptionsDefaults.frame = false;
+		electronOptionsDefaults.transparent = true;
+		electronOptionsDefaults.hasShadow = false;
 	}
 
 	const electronOptions = Object.assign({}, electronOptionsDefaults, config.electronOptions);
@@ -117,6 +119,11 @@ function createWindow() {
 
 		callback({ responseHeaders: curHeaders });
 	});
+
+	mainWindow.once("ready-to-show", () => {
+		mainWindow.setFullScreen(true);
+		mainWindow.show();
+	});
 }
 
 // This method will be called when Electron has finished