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Re: [pygame] Re: circular movement in pygame

Not sure if this is what you're looking for, but I would also use cos for the x coordinate as suggested. If:

self.rect.x = self.radius * math.cos(self.angle) + self.center_x
self.rect.y = self.radius * math.sin(self.angle) + self.center_y

Take a derivative (assume: Âangle += angular_vel * dt for every increment in time dt), so that:

self.rect.x += -self.radius * math.sin(self.angle) * self.angular_vel * dt
self.rect.y += self.radius * math.cos(self.angle) * self.angular_vel * dt

After a while, it won't be a perfect circle anymore (because of accumulating errors), or the center may move across the screen, but it may work for quite some time.

Best,
Lucas

On Tue, Apr 28, 2015 at 9:44 PM, diliup gabadamudalige <diliupg@xxxxxxxxx> wrote:
I am pasting the code of the complete program of around 145 lines below with the part that works correctly and the part that doesn't marked.Â

Why does the object NOT move in a circle when implemented as a class?

import sys, os, pygame, itertools
from math import sin,cos,pi, radians
from pygame.locals import *

os.environ['SDL_VIDEO_WINDOW_POS'] = "%d,%d" % (50,50) #Set window position

pygame.init()
clock = pygame.time.Clock()
FPS = 1000

SCREENW = 800 Â #screen width
SCREENH = 740 Â #screen height

BLACK = (0, 0, 0)
BLUE = (0, 0, 255)
ORANGE = (128, 100, 30)
FONT1= "Cookie-Regular.ttf"

SCREEN = pygame.display.set_mode((SCREENW, SCREENH), 0, 32) #display screen
clock = pygame.time.Clock()

#-------------------------------------------------------------------------------
def maketext(msg,fontsize, colour = ORANGE, font = FONT1):
  mafont = pygame.font.Font(font, fontsize)
  matext = mafont.render(msg, True, colour)
  matext = matext.convert_alpha()
  return matext

#-------------------------------------------------------------------------------
def print_info():
  """"""
  textcos = maketext(str(round(obj.rect.x, 2)) + "  " + str(round(obj.rect.y, 2)), 30)
  SCREEN.blit(textcos, (obj.rect.x, obj.rect.y + 30))

#-------------------------------------------------------------------------------
class object_factory(pygame.sprite.Sprite):

  def __init__(self, imagelist, xpos, ypos):
    """Constructor"""
    pygame.sprite.Sprite.__init__(self)
    self.name = ""
    self.frame = 0
    self.imagelist = imagelist
    self.image = imagelist[self.frame]
    self.mask = pygame.mask.from_surface(self.image) # pixelmask
    self.rect = self.image.get_rect()
    self.rect.x = xpos
    self.rect.y = ypos
    self.timer = 0
    self.timerlimit = 10

    #----------------------------------------------------------------------
  #def move(self): Â# wallsprites, Herosprite, looptime
    #self.rect.x += self.speedx
    #self.rect.y += self.speedy

  #----------------------------------------------------------------------
  def update(self):
    """"""
    self.image = self.imagelist[self.frame]
    if self.timer >= self.timerlimit:
      self.frame += 1
      if self.frame >= len(self.imagelist):
        self.frame = 0
      self.timer = 0
    self.timer += 1

plat = pygame.image.load("plt0.png").convert_alpha()
star = pygame.image.load("gemp0.png").convert_alpha()

## declare the sprite group
platforms = pygame.sprite.Group()
boxes = pygame.sprite.Group()

rotcenx = SCREENW/2
rotceny = SCREENH/2

radius = 200
angle = radians(90) Â#pi/4 # starting angle 45 degrees
omega = radians(5) #Angular velocity

m = rotcenx + radius * cos(angle) #Starting position x
n = rotceny - radius * sin(angle) #Starting position y

for _ in itertools.repeat(None, 1):
  midx = SCREENW/2
  midy = SCREENH/2

  radius1 = 200
  angle1 = radians(180) Â#pi/4 # starting angle 45 degrees
  angular_v = radians(5) #Angular velocity

  a = midx + (radius1 * cos(angle1)) #Starting position x
  b = midy - (radius1 * sin(angle1)) #Startinh position y

  plat = object_factory([plat], a, b)
  plat.radius = radius1
  plat.angle = angle1
  plat.angular_vel = angular_v


  platforms.add(plat)

while True:
  ms = clock.tick(FPS) Â# milliseconds passed since last frame

  SCREEN.fill((BLACK))

  ## THIS CODE WORKS MOVES THE OBJECT IN A CIRCLE
 ÂÂ
  SCREEN.blit(star, (m, n)) # Draw current x,y

  angle = angle + omega # New angle, we add angular velocity

  m = m + radius * omega * cos(angle + pi / 2) # New x

  n = n - radius * omega * sin(angle + pi / 2) # New y

  ##---------------------------------------------------------------
  # show object anchored to center of rotation
  pygame.draw.line(SCREEN, ORANGE, (rotcenx, rotceny), (m, n))

  text = maketext(str(radius), 30)
  SCREEN.blit(text, (m, n - 40))

  text = maketext((str(round(m, 2)) + " Â" + str(round(n, 2))), 30)
  SCREEN.blit(text, (m, n + 40)) # Draw current x,y

  ## THIS CODE DOES NOT MOVE THE OBJECT IN A CIRCLE

  for plat in platforms:

    plat.angle = plat.angle + plat.angular_vel

    plat.rect.x = plat.rect.x + plat.radius * plat.angular_vel * cos(plat.angle + pi / 2)

    plat.rect.y = plat.rect.y - plat.radius * plat.angular_vel * sin(plat.angle + pi / 2)

  ##------------------------------------------------------------------------

  pygame.draw.line(SCREEN, ORANGE, (midx, midy), (plat.rect.x, plat.rect.y))
  pygame.draw.circle(SCREEN, BLUE, (rotcenx, rotceny), radius1, 2)

  platforms.update()
  platforms.draw(SCREEN)

  pygame.event.pump()
  keys = pygame.key.get_pressed()

  for event in pygame.event.get():
    if event.type == QUIT or (event.type == KEYDOWN and event.key == K_ESCAPE):
      pygame.quit()
      sys.exit()

  pygame.display.update()
  pygame.time.wait(100)


On Tue, Apr 28, 2015 at 6:22 PM, diliup gabadamudalige <diliupg@xxxxxxxxx> wrote:
Looking at the code on this page lines 47 & 48

http://programarcadegames.com/python_examples/show_file.php?file=sprite_circle_movement.py

is there a way to doÂ
self.rect.x += some value
self.rect.y += some value

rather than

self.rect.x = self.radius * math.sin(self.angle) + self.center_x
self.rect.y = self.radius * math.cos(self.angle) + self.center_y

?

I tired it in the code attached and strangely it works ok but only OUTSIDE THE class. When I implement the exact code in a class it does something weird. I can't find where I have gone wrong.

Please help.

Many thanks in advance.

Diliup Gabadamudalige


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--
Diliup Gabadamudalige

http://www.diliupg.com
http://soft.diliupg.com/

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--
"""
 lucas o. wagner, PhD
 theoretical physics/chemistry
"""