I thank all those who responded to my question
Here is the code that I had written.
When updating is applied to a surface object the rotation works but when it
is applied through a class to an object it goes wrong in about 3 rotations.
As far as I can see the code is the same. What is wrong? If you can correct
some code and show me would help.
On Tue, Apr 28, 2015 at 11:58 PM, Oscar Benjamin <oscar.j.benja...@gmail.com
> wrote:
> On 28 April 2015 at 16:38, diliup gabadamudalige <dili...@gmail.com>
> 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 do
> > 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
>
> There's no way to do that. The second version ignores the previous
> value of self.rect.x/y.
>
> I'm going to guess that the angle has only changed by a small amount
> delta_angle between iterations in which case there would be a way to
> do it approximately.
>
> The real question is just why though? The second version is correct
> and will be correct for ever. The first version would only be
> approximately correct and over time you'd probably find that the
> position would drift so that the ball was effectively at a different
> radius.
>
> In any case if
> x = r * sin(theta)
> then
> dx/dt = r * cos(theta) * dtheta/dt.
> Since
> y = r * cos(theta) that's
> dy/dt = x * dtheta/dt.
> So you could update y approximately with:
> y += x * dtheta/dt * deltat
> where deltat is your timestep. In your code that would be:
> self.rect.x += self.rect.y * self.speed
> self.rect.y -= self.rect.x * self.speed
>
> Really what you have now is better though.
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--
Diliup Gabadamudalige
http://www.diliupg.com
http://soft.diliupg.com/
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**********************************************************************************************
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 #screen width
SCREENH = 740 #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, speedx = 0, speedy = 0, value =
0):
"""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.speedx = speedx
#self.speedy = speedy
self.timer = 0
self.timerlimit = 10
#----------------------------------------------------------------------
#def move(self): # 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()
#box = pygame.image.load("crateB.png").convert_alpha()
platforms = pygame.sprite.Group()
boxes = pygame.sprite.Group()
rotcenx = SCREENW/2
rotceny = SCREENH/2
radius = 200
angle = radians(90) #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):
madyax = SCREENW/2
madyay = SCREENH/2
araya = 200
konaya = radians(180) #pi/4 # starting angle 45 degrees
konika_pravegaya = radians(5) #Angular velocity
a = madyax + (araya * cos(konaya)) #Starting position x
b = madyay - (araya * sin(konaya)) #Startinh position y
plat = object_factory([plat], a, b)
plat.araya = araya
plat.konaya = konaya
plat.kp = konika_pravegaya
platforms.add(plat)
while True:
ms = clock.tick(FPS) # milliseconds passed since last frame
#looptime = milliseconds / 1000.0 # seconds passed since last frame
SCREEN.fill((BLACK))
pygame.draw.circle(SCREEN, BLUE, (SCREENW / 2, SCREENH / 2), 5)
##-----------------------------------------------------------
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)) + " " + str(round(n, 2))), 30)
SCREEN.blit(text, (m, n + 40)) # Draw current x,y
##------------------------------------------------------------------
for plat in platforms:
plat.konaya = plat.konaya + plat.kp
plat.rect.x = plat.rect.x + plat.araya * plat.kp * cos(plat.konaya + pi
/ 2)
plat.rect.y = plat.rect.y - plat.araya * plat.kp * sin(plat.konaya + pi
/ 2)
##------------------------------------------------------------------------
pygame.draw.line(SCREEN, ORANGE, (madyax, madyay), (plat.rect.x,
plat.rect.y))
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)
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