How to make an image in pygame stay still when rotated?

Question

So I'm trying to make an image point towards the mouse at all times, and it sorta works. The image points towards the mouse, but it's moving around a bit. I don't know if it is a problem with the image or something, but any help would be appreciated. Just in case you don't know, direction is calculated by taking the difference between the mouse pos and image pos, running it through the atan function, dividing it by 6.28, and then multiplying by 360. This will result in the degree your mouse it at from the image. Here's the code. Also, I'm supposed to attribute the developer of the image, so here. Icons made by mynamepong from www.flaticon.com

import pygame
import math
pygame.init()
win_height=800
win_width=800
win=pygame.display.set_mode((win_width,win_height))
pygame.display.set_caption("Rotation Test")

black=(0,0,0)

carx=200
cary=200

clock=pygame.time.Clock()
car=pygame.image.load("inkscape images for games/car.png")
car=pygame.transform.scale(car,(100,100))

while True:
    mouse=pygame.mouse.get_pos()
    clock.tick(60)
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            pygame.quit()
    angle=math.atan2(mouse[0]-carx,mouse[1]-cary)/6.28*360
    win.fill(black)
    car_rotated=pygame.transform.rotate(car,angle)
    win.blit(car_rotated,(carx,cary))
    pygame.display.update()

Just change: `win.blit(car_rotated, car_rotated.get_rect(center = (carx,cary)))`. I recommend reading the answer to the questions linked above. — Rabbid76, Oct 28 '20 at 05:41

Mike67 · Accepted Answer · 2020-10-28T03:52:20.003

You need to set the car center then rotate the car around that point.

Try this code:

import pygame
import math
pygame.init()
win_height=800
win_width=800
win=pygame.display.set_mode((win_width,win_height))
pygame.display.set_caption("Rotation Test")

black=(0,0,0)

# center of car rect
carx=400
cary=400

clock=pygame.time.Clock()
car=pygame.image.load("inkscape images for games/car.png")
car=pygame.transform.scale(car,(100,100))

while True:
    mouse=pygame.mouse.get_pos()
    clock.tick(60)
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            pygame.quit()

    angle=math.atan2(mouse[0]-carx,mouse[1]-cary)/6.28*360-90
    win.fill(black)
    car_rotated=pygame.transform.rotate(car,angle)
    new_rect = car_rotated.get_rect(center = (carx, cary))
    win.blit(car_rotated,(new_rect.x,new_rect.y))
    pygame.display.update()

Output

Please mention that the computation of the angle is wrong. The angle is computed by `atan2(y, x)` (instead of `atan2(x, y)`). The contributor ignored my advice and swapped `sin` and `cos`. Compensating for this error by swapping `sin` and `cos` compensates for one error with another error. See [Why are my bullets travelling at a 90 degree angle from the mouse?](https://stackoverflow.com/questions/64580873/why-are-my-bullets-travelling-at-a-90-degree-angle-from-the-mouse). — Rabbid76, Oct 28 '20 at 21:51

score 0 · Answer 2 · answered Oct 28 '20 at 03:31

It looks like pygame moves the image if you rotate it at any angle other than a right angle. To get around this you'll have to keep track of the previous center position of the image and update it every frame. Try something like this:

car_rotated=pygame.transform.rotate(car,angle)
new_rect = car_rotated.get_rect(center = car.get_rect().center)
win.blit(car_rotated,new_rect)

The code looked like it was rotating correctly when I tested it, but it still looked a little weird for some reason. Let me know if this is what you're going for.

How to make an image in pygame stay still when rotated?

2 Answers2

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