pygame在窗口未聚焦时捕获键盘事件

Question

I wrote a simple python script that gives control over the cursor to a joystick. My way to find out how this works is documented here . Now that works flawlessly but, as soon as I start the script to use the joystick, the mouse is useless, because my python routine sets the value back to its original, whenever a new joystick event comes in.

Thus I want my joystick events to be ignored as long as a key of the keyboard is pressed. I came across the pygame.key.get_pressed() method but this seems to work only, if the pygame window is in focus. I want this script running in background. Should I start using non-pygame events to listen to the keyboard or are there ways to keep track of the keyboard events analogue to the joystick events, which are recognized in background, via pygame?

Answer 1

I expect pygame sets up its own "sandbox" so that it's hard to detect input from outside its window. Your previous question indicates that you are also using the win32api module. We can use that to detect global key presses.

The correct way to detect key presses at the global scope is to set up a keyboard hook using SetWindowsHookEx . Unfortunately, win32api does not expose that method, so we'll have to use a less efficient method.

The GetKeyState method can be used to determine whether a key is down or up. You can continuously check the state of a key to see if the user has pressed or released it lately.

import win32api
import time

def keyWasUnPressed():
    print "enabling joystick..."
    #enable joystick here

def keyWasPressed():
    print "disabling joystick..."
    #disable joystick here

def isKeyPressed(key):
    #"if the high-order bit is 1, the key is down; otherwise, it is up."
    return (win32api.GetKeyState(key) & (1 << 7)) != 0


key = ord('A')

wasKeyPressedTheLastTimeWeChecked = False
while True:
    keyIsPressed = isKeyPressed(key)
    if keyIsPressed and not wasKeyPressedTheLastTimeWeChecked:
        keyWasPressed()
    if not keyIsPressed and wasKeyPressedTheLastTimeWeChecked:
        keyWasUnPressed()
    wasKeyPressedTheLastTimeWeChecked = keyIsPressed
    time.sleep(0.01)

Warning: as with any "while True sleep and then check" loop, this method may use more CPU cycles than the equivalent "set a callback and wait" method. You can extend the length of the sleep period to ameliorate this, but the key detection will take longer. For example, if you sleep for a full second, it may take up to one second between when you press a key and when the joystick is disabled.

Answer 2

when your window gains or looses focus you get an ACTIVEEVENT . It's gain and state attributes tell you which state you've gained or lost. The easisest solution would probably be to catch this events in your main event loop and use them to keep track weather you have focus or not. Then you can just ignore joystick events if you don't have the focus.