Re: [pygame] Yeah looks like i'm doing quite well so far, completed my goal for today.

["Lamonte Harris" <pyth0nc0d3r@xxxxxxxxx>]

Okay I'm a bit confused with the whole surfaces[i].image I understand how to assign rects and all but what I mean is how would I go about making that class into a list?

On 9/10/07, Ethan Glasser-Camp <glasse@xxxxxxxxxx> wrote:

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Lamonte Harris wrote:
> class map_:
>     def __init__(self,block=100,wndow=(300,300)):
>         self.BLOCK = block
>         self.size = wndow
>         self.map = []
>         self.surfaces = [[],[]]
>         self.window = pygame.display.set_mode(self.size)
>         pygame.init()
>     def create_box(self,size,color,rect):
>         box = pygame.Surface((size))
>         pygame.draw.rect(box,color,box.get_rect())
>         self.surfaces[0].append(box)
>         self.surfaces[1].append(rect)
>
> Can you explain a little more.

I can explain a lot more.

In your code, you have a structure called "surfaces", which is kept in
the map class. This structure is a list with two elements. These two
elements are themselves lists -- the first one is a list of Surface
objects, representing images, and the second one is a list of some
type representing location of these images on-screen. In the code
snippet above, your map "create_box" method adds an image and a
location to this "surfaces" structure. These two things, image and
location, are "paired", in a sense; the image has a location, and
putting a different image at the same location, or putting the same
image at a different location, would be a bug.

Pairing information in this way is very common in all kinds of
programs, not just games, and there are many mechanisms for showing
this kind of pairing. You have implemented a mechanism which I will
call "parallel arrays"; in order to access an image and its
corresponding location, you look up the same index in two lists
(surfaces[0][i] and surfaces[1][i]). This is a simple mechanism, and
it works fine, but there are some complications. For instance, let's
say you have five images, and five locations. Now you want to delete
an image, but forget to delete its location. Now you have four images
and five locations, and it may not be possible to figure out which
image goes with which location.

I am proposing the use of another structure, which is called "sprite"
here but can really be called anything, which combines both the image
and the location. If you were to structure your map_ class this way,
instead of having "structures" be a list of two lists, it would be one
list of sprites. To access the image and the location, you would do
surfaces[i].image and surfaces[i].rect. In addition, you no longer
have to worry about deleting all the parts of the sprite object; once
the sprite is removed from the "surfaces" list, it's gone, not
"half-there" like in the hypothetical "forgot to delete something" case.

There is more to pygame sprites, but the reason I suggested you use
them is that they keep the image and its location together.

This is the "why". The "how" is outlined in the code I sent -- it
creates one sprite, and uses its "image" and "rect" attributes to
simplify moving it around onscreen (in an admittedly trivial way). As
it applies to your own code you can probably figure out on your own.

HTH,

Ethan
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