Pygame mouse event.rel not working outside window

Question

I'm trying to implement a feature in Pygame where if the user moves the mouse outside the window the relative position (event.rel) can be returned. I'm trying to do this because I want to make a game where you can keep turning left or right from mouse input.

I know this is possible from the docs:

If the mouse cursor is hidden, and input is grabbed to the current display the mouse will enter a virtual input mode, where the relative movements of the mouse will never be stopped by the borders of the screen. See the functions pygame.mouse.set_visible() and pygame.event.set_grab() to get this configured.

For this reason, I've implemented these lines in my code

pygame.mouse.set_visible(False)
pygame.event.set_grab(True)

However this doesn't help. The actual behaviour is:

when the mouse is moving in the window, event.rel prints to the console (expected)
when the mouse is moving outside the window, event.rel doesn't print to the console (not expected)

Other strange behaviour:

Initially event.rel is set to (300, 300) which is the center of my 600x600 screen. Ideally initial event.rel should be (0,0)

Possible cause:

I'm running the code below in trinket.io or repl.it. Because this is a browser the demo window might cause problems. Maybe this is solved by downloading python locally but i don't want to do this as it takes up too much space (my laptop sucks) and also it would be good to have an online demo to easily show employers that are too lazy to paste code into their IDEs.

Similar issue: This guy on reddit had a very similar issue but I think his solution is not related to my situation

This block of code was what I asked originally but it doesn't demonstrate the question as well as the last block. Please scroll down to see the last block of code instead :)

import pygame
pygame.init()

# screen
X = 600  # width
Y = 600  # height
halfX = X/2
halfY = Y/2
screen = pygame.display.set_mode((X, Y), pygame.FULLSCREEN)
clock = pygame.time.Clock()

# Colors
WHITE = (255, 255, 255)
RED = (255, 0, 0)

# From the docs:
# "If the mouse cursor is hidden, and input is grabbed to the 
# current display the mouse will enter a virtual input mode, where 
# the relative movements of the mouse will never be stopped by the 
# borders of the screen."
pygame.mouse.set_visible(False)
pygame.event.set_grab(True)

def drawCross(point, size, color):
  pygame.draw.line(screen, color, (point[0]-size,point[1]-size), (point[0]+size,point[1]+size), 2)
  pygame.draw.line(screen, color, (point[0]+size,point[1]-size), (point[0]-size,point[1]+size), 2)

canvas_rel = (halfX,halfY)

running = True
while running:

  for event in pygame.event.get():
    if event.type == pygame.MOUSEMOTION:
      print('event.rel = ' + str(event.rel))
      canvas_rel = [10 * event.rel[0] + halfX, 10 * event.rel[1] + halfY]
      print(' canvas_rel = ' + str(canvas_rel))

    if event.type == pygame.KEYDOWN and event.key == pygame.K_ESCAPE:
      print('escape')
      running = False
      break

  screen.fill(WHITE)

  # Red sight to represent pygame mouse event.rel
  drawCross(canvas_rel, 10, RED)

  pygame.display.flip()
  clock.tick(20)

pygame.quit()

EDIT:

The above code doesn't fully demonstrate my problem. I've added a better sample below to make the the question easier to understand. This sample will draw a triangle in the centre of the screen. The triangle will rotate with relative horizontal motion of the mouse. Note the attempt to use pygame.mouse.set_pos

import pygame
from math import pi, cos, sin

pygame.init()

# screen
X = 600  # width
Y = 600  # height
halfX = X/2
halfY = Y/2
screen = pygame.display.set_mode((X, Y), pygame.FULLSCREEN)
clock = pygame.time.Clock()

# for getting relative mouse position when outside the screen
pygame.mouse.set_visible(False)
pygame.event.set_grab(True)

# Colors
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

# sensitivity
senseTheta = 0.01

# player
stand = [halfX, halfY]
t = 0 # angle in radians from positive X axis to positive x axis anticlockwise about positive Z

# draws a white cross in the screen center for when shooting is implemented :)
def drawPlayer(): 
  p = stand
  d = 50

  a1 = 0.25*pi-t
  a2 = 0.75*pi-t

  P = (p[0],p[1])
  A1 = (p[0] + d*cos(a1), p[1] + d*sin(a1)) # P + (d*cos(a1), d*sin(a1))
  A2 = (p[0] + d*cos(a2), p[1] + d*sin(a2)) # P + (d*cos(a2), d*sin(a2))

  pygame.draw.line(screen, BLACK, P, A1, 2)
  pygame.draw.line(screen, BLACK, A1, A2, 2)
  pygame.draw.line(screen, BLACK, A2, P, 2)

running = True
while running:

  for event in pygame.event.get():

    if event.type == pygame.MOUSEMOTION:
      mouseMove = event.rel
      print('mouseMove = ' + str(mouseMove))

      t -= mouseMove[0] * senseTheta

      # "Fix" the mouse pointer at the center
      # pygame.mouse.set_pos((screen.get_width()//2, screen.get_height()//2))
      # But I think set_pos triggers another MOUSEMOTION event as moving in positive x
      # seems to move backward the same amount in x (i.e. the triangle doesn't
      # rotate). See the console log.
      # If you uncomment this line it works ok (the triangle rotates) but still 
      # glitches when the mouse leaves the window.
      # uncommented or not I still cant get the mouse to work outside the window

    if event.type == pygame.KEYDOWN:
      if event.key == pygame.K_ESCAPE:
        running = False
        break

  screen.fill(WHITE)

  drawPlayer()

  pygame.display.flip()
  clock.tick(40)

pygame.quit()

Pygame mouse event.rel not working outside window

0 Answers0