Create virtual key up events for all pressed keys when the display loses focus.

This is a workaround for missed key events and incorrect key state reporting. This is actually a cleaner solution to the previous workaround on Windows and works nicely on Linux too.

src/java/org/lwjgl/opengl/LinuxDisplay.java

@@ -1125,6 +1125,8 @@ final class LinuxDisplay implements DisplayImplementation {
 	private void releaseInput() {
 		if (isLegacyFullscreen() || input_released)
 			return;
+		if ( keyboard != null )
+			keyboard.releaseAll();
 		input_released = true;
 		updateInputGrab();
 		if (current_window_mode == FULLSCREEN_NETWM) {

src/java/org/lwjgl/opengl/LinuxKeyboard.java

@@ -296,7 +296,7 @@ final class LinuxKeyboard {
 		return keycode;
 	}
 
-	private byte getKeyState(int event_type) {
+	private static byte getKeyState(int event_type) {
 		switch (event_type) {
 			case LinuxEvent.KeyPress:
 				return 1;
@@ -307,10 +307,22 @@ final class LinuxKeyboard {
 		}
 	}
 
+	/** This is called when the window loses focus: we release all currently pressed keys. */
+	void releaseAll() {
+		for ( int i = 0; i < key_down_buffer.length; i++ ) {
+			if ( key_down_buffer[i] != 0 ) {
+				key_down_buffer[i] = 0;
+				putKeyboardEvent(i, (byte)0, 0, 0L, false);
+			}
+		}
+	}
+
 	private void handleKeyEvent(long event_ptr, long millis, int event_type, int event_keycode, int event_state) {
 		int keycode = getKeycode(event_ptr, event_state);
 		byte key_state = getKeyState(event_type);
 		boolean repeat = key_state == key_down_buffer[keycode];
+		if ( repeat && event_type == LinuxEvent.KeyRelease ) // This can happen for modifier keys after losing and regaining focus.
+			return;
 		key_down_buffer[keycode] = key_state;
 		long nanos = millis*1000000;
 		if (event_type == LinuxEvent.KeyPress) {

src/java/org/lwjgl/opengl/WindowsDisplay.java

@@ -362,7 +362,7 @@ final class WindowsDisplay implements DisplayImplementation {
 	/*
 	 * Called when the application is alt-tabbed to or from
 	 */
-	private void appActivate(boolean active) {
+	private void appActivate(boolean active, long millis) {
 		if (inAppActivate) {
 			return;
 		}
@@ -379,14 +379,15 @@ final class WindowsDisplay implements DisplayImplementation {
 			redoMakeContextCurrent = true;
 			if (Display.isFullscreen())
 				updateClipping();
-
+		} else {
 			if ( keyboard != null )
-				keyboard.fireLostKeyEvents();
-		} else if (Display.isFullscreen()) {
-			showWindow(getHwnd(), SW_SHOWMINNOACTIVE);
-			resetDisplayMode();
-		} else
-			updateClipping();
+				keyboard.releaseAll(millis);
+			if ( Display.isFullscreen() ) {
+				showWindow(getHwnd(), SW_SHOWMINNOACTIVE);
+				resetDisplayMode();
+			} else
+				updateClipping();
+		}
 		updateCursor();
 		inAppActivate = false;
 	}
@@ -997,10 +998,10 @@ final class WindowsDisplay implements DisplayImplementation {
 					return defWindowProc(hwnd, msg, wParam, lParam);
 				}
 			case WM_KILLFOCUS:
-				appActivate(false);
+				appActivate(false, millis);
 				return 0L;
 			case WM_SETFOCUS:
-				appActivate(true);
+				appActivate(true, millis);
 				return 0L;
 			case WM_MOUSEACTIVATE:
 				if ( parent != null ) {

src/java/org/lwjgl/opengl/WindowsKeyboard.java

@@ -122,6 +122,18 @@ final class WindowsKeyboard {
 		return (GetAsyncKeyState(virt_key) & 0x8000) != 0;
 	}
 
+	/**
+	 * This is called when the window loses focus: we release all currently pressed keys. If a key has been pressed (or hasn't been released at all), before we
+	 * regain focus, we'll start receiving repeat press events. We'll treat the first of those as a non-repeat press.
+	 */
+	void releaseAll(long millis) {
+		for ( int i = 0; i < virt_key_down_buffer.length; i++ ) {
+			if ( isKeyPressed(virt_key_down_buffer[i]) ) {
+				handleKey(i, 0, false, (byte)0, millis, false);
+			}
+		}
+	}
+
 	void handleKey(int virt_key, int scan_code, boolean extended, byte event_state, long millis, boolean repeat) {
 		virt_key = translateExtended(virt_key, scan_code, extended);
 		if ( !repeat && isKeyPressed(event_state) == isKeyPressed(virt_key_down_buffer[virt_key]) )
@@ -132,6 +144,7 @@ final class WindowsKeyboard {
 		int keycode = WindowsKeycodes.mapVirtualKeyToLWJGLCode(virt_key);
 		if (keycode < key_down_buffer.length) {
 			key_down_buffer[keycode] = event_state;
+			repeat &= isKeyPressed(virt_key_down_buffer[virt_key]); // Treat the first repeat event after releaseAll() as a non-repeat press.
 			virt_key_down_buffer[virt_key] = event_state;
 		}
 		retained_key_code = keycode;
@@ -141,13 +154,6 @@ final class WindowsKeyboard {
 		retained_repeat = repeat;
 	}
 
-	void fireLostKeyEvents() {
-		for ( int i = 0; i < virt_key_down_buffer.length; i++ ) {
-			if ( isKeyPressed(virt_key_down_buffer[i]) && !isKeyPressedAsync(i) )
-				handleKey(i, 0, false, (byte)0, 0L, false);
-		}
-	}
-
 	void handleChar(int event_char, long millis, boolean repeat) {
 		if (has_retained_event && retained_char != 0)
 			flushRetained();