Re: [pygame] Making a clock rotate

[Robert Mark Waugh <robert@waugh.com>]

Hi dialtone:

I'm not exactly sure what you're trying to do with these trig functions, 
but I'm going to guess you're trying to keep the object's center at the 
original center even though the rotated rect grows as it rotates away 
from an increment of pi/2.  What you really want to do is what I 
included below.  Notice that if you have a square rotating inside 
another square, while the original square is constant in size, whatever 
is in the center and extends out to a center of the inner square will 
form a circle in it's rotation.  If you take the outer square and divide 
it up into four equal areas and attach the four inner corners of the 
inner square to the edges of the outer square you will see that the 
offset of the inscribed cirlce of rotation from the upper left corner is 
exactly (.5outer_x-.5inner_x, .5outer_y-.5inner_y).  If you have an 
image in the inner rect, you need to be careful to make sure that it 
exists entirely within the inscribed circle of rotation of the inner 
rectange.  This is easy to do.  The radius of this inscribed circle is 
exactly 1/2 the dimension of the original square.  You can write 
something that does this with rectangles, but instead of a cirlce of 
rotation you will have an ellipse, and the implementation is a little 
more complex.  There's no reason for that, since it should be a matter 
of gimp'ing your original image to make it into a square.

Good luck,
robert

import pygame
from pygame.locals import *
import time
import math

def load_image(name, colorkey=None):
   try:
       image = pygame.image.load(name)
   except pygame.error, message:
       print 'Cannot load image:', name
       return None
   image = image.convert()
   if colorkey is not None:
       if colorkey is -1:
           colorkey = image.get_at((0,0))
       image.set_colorkey(colorkey, RLEACCEL)
   return image, image.get_rect()

def recentered(new, original):
   new_rect = new.get_rect()
   orig_rect = original.get_rect()
   xoffset = new_rect[2]*.5-orig_rect[2]*.5
   yoffset = new_rect[3]*.5-orig_rect[3]*.5
   cropped_rect = new.subsurface((xoffset, yoffset, orig_rect[2], 
orig_rect[3]))
   return cropped_rect

class orologio:
   def __init__(self):
       self.quadrante = pygame.display.set_mode((256,256))
       self.original, self.rect = 
load_image('/home/dialtone/Documents/lancetta.jpg')
       self.rect = (126, 0, self.rect[2], self.rect[3])            # 
Adjust rectangle
       self.orig_rect = self.rect[:]
       self.quadrante.blit(self.original, self.rect)

   def update(self, degree):
       self.degree = degree
       self.image = pygame.transform.rotate(self.original, self.degree)
       self.rect = self.image.get_rect()
       self.image = recentered(self.image, self.original)
       print self.image.get_rect(), self.rect
       self.quadrante.blit(self.image, self.rect)
       pygame.display.update()
       pygame.time.wait(1000)

if __name__=='__main__':
   pygame.init()
   clock = orologio()
   degrees = 0
   quit = None
   while not quit:
       if abs(degrees) >= 360:
           degrees = 0
       clock.update(degrees)
       degrees -= 6
       for event in pygame.event.get():
           if event.type == KEYDOWN:
               print "posting quit"
               pygame.event.post(pygame.event.Event(QUIT))
               quit = 1