Re: [pygame] newbie question--> rendeing order

[Pete Shinners <pete@shinners.org>]

enrike@ixi-software.net wrote:
> I was wondering if there is some way to change the rendering order 
> of a group of sprites "on the fly". I want to bring the clicked sprite 
> above the others.
> So far i have manage to do it by storing a reference of the sporites 
> in a list, change the order of that list, remove all objects from the 
> rendering group and adding the whole list back again to the group.
it isn't hard to write new sprite groups that have different 'draw' 
functions. but your problem will still be ordering the list of sprites.

the standard sprite groups use dictionaries internally for storing the 
sprites. this gives them several bonuses, like very fast searching and 
adding/removing of sprites. unfortunately it also means no sorting.

if we're talking less than 100 or so sprites total, i believe sorting 
the list everytime we draw would be fast enough (although not totally 
efficient). if all sprites have a "pickorder" field with ascending 
numbers, the following sprite group would do the rendering for you..



#note, this is largely 'cut&paste' from the RenderUpdates code
#note, all the complexity from this code comes from managing the
#      update rectangles

class RenderPickOrder(pygame.sprite.RenderUpdates):
    """render sprites in the order of their 'pickorder' field"""
    def draw(self, surface):
        dirty = self.lostsprites
        self.lostsprites = []
        allsprites = self.spritedict.sprites()
        allsprites.sort(lambda a,b: cmp(a[0].pickorder, b[0].pickorder))
        for s,r in allsprites:
            newrect = surface.blit(s.image, s.rect)
            if r is 0:
                dirty.append(newrect)
            else:
                if newrect.colliderect(r):
                     dirty.append(newrect.union(r))
                else:
                     dirty.append(newrect)
                     dirty.append(r)
            self.spritedict[s] = newrect
     return dirty



when you need to press more performance out. i believe you will need to 
create a new type of sprite group that doesn't use a dictionary. your 
best bet is probable a regular list, or a priority queue container 
(there are several in the asdn cookbook).

check the source of the pygame.sprite module, it has extra documentation 
for creating your own classes, but it's easiest to carve and paste what 
you need.
http://cvs.seul.org/cgi-bin/cvsweb-1.80.cgi/games/pygame/lib/sprite.py?rev=1.22