Re: [pygame] Alpha Channel Speed Question

["Lenard Lindstrom" <len-l@xxxxxxxxx>]

On 22 Nov 2006 at 21:15, Kamilche wrote:

> I have a question - Do you know of a way to get method 3 as outlined 
> below to be faster? The necessity of doing all those extra blits to 
> preserve the alpha channel is really slowing things down.
> 
> 
> 
> 
> import pygame
> 
[snip some code]
> def Run():
>      bgcolor1 = (255, 255, 255)
>      bgcolor2 = (192, 192, 192)
>      bgcolor3 = (128, 128, 128)
>      nightcolor = [0, 0, 0, 64]
> 
>      # Create a bitmap - assume this is an expensive operation
>      # taking a few seconds.
>      bitmap = pygame.Surface((100, 100), pygame.SRCALPHA, 
> 32).convert_alpha()
>      pygame.draw.circle(bitmap, (0, 255, 255), [50, 50], 50, 0)
>      bitmappos = [0, 0]
> 
>      # Create the nighttime overlay
>      night = pygame.Surface((WIDTH, HEIGHT/3), pygame.SRCALPHA, 
> 32).convert_alpha()
>      night.fill(nightcolor)
> 
>      # Loop forever
>      quitgame = 0
>      while not quitgame:
>          pygame.event.pump()
[snip]
>          # Look for quit
>          for e in pygame.event.get():
>              if e.type in [pygame.QUIT, pygame.MOUSEBUTTONDOWN]:
>                  quitgame = 1
>                  break
>              elif e.type == pygame.KEYDOWN:
>                  if e.key == 27:
>                      quitgame = 1
>                      break
>              elif e.type == pygame.MOUSEMOTION:
>                  bitmappos = e.pos
>                  nightcolor[3] = e.pos[0]/float(WIDTH) * 255
>                  night.fill(nightcolor)
> 
Maybe, using colorkey and Surface alpha. But I have a question too. 
Do you prepare all your bitmaps (circle) at game startup? More 
specifically, would it be expensive to prepare a black and white 
mask, to be used as the shader (night), for each bitmap? Even if it 
is you can remove excess processing by declaring night as:

pygame.Surface((WIDTH, HEIGHT/3), 0, 32)

and adjust its surface alpha using set_alpha().

Lenard Lindstrom
<len-l@xxxxxxxxx>