Re: [pygame] animatio of drawned images

[Pete Shinners <pete@visionart.com>]

s.jol wrote:

> I would like to know how do I do animations using sprites or draw functions?
> I have tried to load sprites but it does not work, I have tried to move the
> circles I draw but even after an update there is no change. I import the
> following:


well, you're not the first person to get stuck at this point. i've been 
thinking about putting together a very basic introducion/tutorial for 
people like you first getting started with graphics programming. let's 
look at your code...

> screen = pygame.display.set_mode((500,400))
> ship = pygame.draw.circle(screen,(20,200,123),(300,200),45,12)
> ship.move(23,34)


there is nothing really special about the "screen" surface. it just

represents pixels that are shown to the user. to make an object (like
this circle) move, we need to draw it in the new position. if we just 
draw it in the new position, we will actually see two circles, the first 
circle in the original position, and a second circle in the new 
position. so before we redraw the circle, we'll want to erase the 
original one.

the pygame.draw functions return a rectangular area of the section of 
the screen that was changed. this doesn't represent anything we can 
actually see, it's just some coordinates that tell us what area has 
changed on the screen. in your code you create a variable named "ship" 
that represents these coordinates on the screen. your call to 
ship.move() is simply moving these coordinates around. again, they are 
not something we can actually see, so this really won't do much.

also, just so you know, your call to ship.move() actually doesn't change 
the position of the ship coordinates. the functions for Rect objects 
usually just return a new copy of the rectangle with whatever changes 
you have asked for. you would probably want to do something like "ship = 
ship.move(23, 34)". in current versions of pygame, there are newer 
"in-place" versions of the Rect functions, which return nothing, but 
effect the real Rectangle, so you could also do it this way, 
"ship.move_ip(23, 34)"

one other thing you'll need to know. the pygame display is double 
buffered. this means what you draw on the screen isn't immediately 
displayed. you'll need to use the special functions 
pygame.display.flip() or pygame.display.update() to actually show what 
you've drawn on the screen.

you should really look through some of the examples that come with 
pygame. in fact take a look at the included "chimp" tutorial, which 
covers a small example with moving images line-by-line.
http://www.pygame.org/docs/tut/ChimpLineByLine.html

taking your above program, what you are expecting the code to do should 
look like this..

	screen = pygame.display.set_mode((500,400))
	color = 20, 200, 123
	pos = 300, 200
	pygame.draw.circle(screen, color, pos, 45, 12)
	pygame.display.flip()  #show our circle
	screen.fill((0, 0, 0)) #erase the screen
	pos[0] = pos[0] + 23   #move circle in x
	pos[1] = pos[1] + 34   #move position in y
	pygame.draw.circle(screen, color, pos, 45, 12)
	pygame.display.flip()  #show our new screen

this would draw a circle, then draw it in another position. 
unfortunately, you probably wouldn't really see it move, since there is 
no delay between drawing the first position and the second position. it 
would happen faster than you could really see it, so you'll only see the 
circle in the second position. perhaps call "pygame.time.delay(500)" 
after calling the first flip() function, so you get a chance to see it.

this code is also very inefficient. erasing the entire screen, when we 
only need to erase the circle will not help this run quickly. there are 
many things you can do to optimize this and make it run faster, but 
hopefully that is what the current tutorials and examples can start to 
show you.



____________________________________
pygame mailing list
pygame-users@seul.org
http://pygame.seul.org