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Re: [pygame] possible to get rid of ghost image after rotating a line?

Hi, Tom,
Have you considered dealing with space mathematically, and rendering the results to screen? 
https://pypi.python.org/pypi/euclid

Here is a different collection of spatial algorithms.
https://bitbucket.org/gummbum/gummworld2/src/6071c5f05c0f2526f5951a08581aefe61d5e4909/gamelib/gummworld2/geometry.py

Gumm

On 8/25/2015 4:25 PM, tom arnall wrote:

I spoke too soon. the use of draw.line() won't work for my application.

I need to be able to easily detect when the line touches a moving
target. Therefore AFIK I need the line to be either a surface or drawn
on a surface, so I can use the surface Rect to check when the  line
collides with a target. I can't see a way to use a line created by
draw.line() to do this.

I also would like the line to behave like the example you referenced,
i.e. to rotate around one of its endpoints, not its center, but this
is a nice-to-have feature; it would also work if the line surface just
rotated around its center.

Tom Arnall

.....
âI have no special talents, only a passionate and stubborn curiosity.â
Albert Einstein





On 8/25/15, Paul Vincent Craven <paul@xxxxxxxxxxxxxxxx> wrote:

I'm not sure why you are creating a new surface everytime. Or why you
create one at all?

Is this similar to what you are looking for?

http://programarcadegames.com/python_examples/f.php?file=radar_sweep.py

Paul Vincent Craven

On Tue, Aug 25, 2015 at 3:57 PM, tom arnall <kloro2006@xxxxxxxxx> wrote:


I want to rotate a line around a point. The code that follows does
this, BUT when it draws a line, it leaves next to the line its ghost.
Is this a problem with pygame, or is there a change I can make in the
code which will make the problem go away?


import pygame, sys
from pygame.locals import *
import time

pygame.init()

#create a surface that will be seen by the user
screen =  pygame.display.set_mode((400, 400))

#create a varible for degrees pf rotation
degree = 0
while True:

     for event in pygame.event.get():
         # quit the game if escape is pressed
         if event.type == QUIT:
             sys.exit()
         elif event.type == KEYDOWN and\
                 event.key == K_ESCAPE:
             sys.exit()

     #clear screen at the start of every frame
     screen.fill((40, 40, 40))

     #create new surface with white BG
     surf =  pygame.Surface((1000, 5))
     surf.fill((255, 255, 255))
     #set a color key for blitting
     surf.set_colorkey((255, 0, 0))


     ##ORIGINAL UNCHANGED
     #where will the static image be placed:
     where = (0,200)

     #draw surf to screen and catch the rect that blit returns
     blittedRect = screen.blit(surf, where)

     ##ROTATED
     #get center of surf for later
     oldCenter = blittedRect.center

     #rotate surf by DEGREE amount degrees
     rotatedSurf =  pygame.transform.rotate(surf, degree)

     #get the rect of the rotated surf and set it's center to the
oldCenter
     rotRect = rotatedSurf.get_rect()
     rotRect.center = oldCenter

     #draw rotatedSurf with the corrected rect so it gets put in the
proper
spot
     screen.blit(rotatedSurf, rotRect)

     #change the degree of rotation
     degree += 5
     if degree > 360:
         degree = 0

     #show the screen surface
     pygame.display.flip()

     #wait 60 ms until loop restart
     pygame.time.wait(60)