Re: [pygame] Re: Strange performance in blit

[bw <stabbingfinger@xxxxxxxxx>]

If you change line 97:

step = 8

and line 112:

elif e.key == K_s: step = 8 if step == 1 else 1

you should see that when X is 8, 24, 40, etc. the problem occurs. When it is 0, 16, 32, 48, etc. it does not occur. The same holds true for the negative X values. 16 is the magic number.

Gumm

On 4/27/2014 01:35, diliup gabadamudalige wrote:

could this be due to the fact operations are done in multiples of 8 bits?

(16 bit, 32 bit, 64 bit etc.)

On Sun, Apr 27, 2014 at 12:52 PM, bw <stabbingfinger@xxxxxxxxx> wrote:

After some more study I have refined the behavior. Thanks to DR0ID for helping me reduce the problem.

In any blit(surf, (x,y)), if x is aligned on a multiple of 16 then blit is fast; otherwise it is slow.

Is this a SDL quirk?

If you have a faster computer than my i3 laptop you may be able to see the problem more clearly with larger tile sizes and screen width.

I've attached another program that is easier to play with, though a bit more complicated to read due to all the run-time controls. You can set the tile size on the fly, and toggle the camera step. Culling is an option just to show rendering off screen has no impact.

Gumm

On 4/26/2014 20:47, bw wrote:

Whoops. Forgive my haste and loss of focus right before sending that. There is a mistake.

Change line 89:
costs = []
to
costs_per_screen = []

Gumm

On 4/26/2014 18:01, bw wrote:

Howdy, folks,

I am getting some strange behavior in Surface.blit(). This is a mystery.

I blit a collection of images to to fill the screen. If I pan left or right even one pixel, blit consumes nearly 4x the CPU. It is only left or right: if I pan up or down performance is not impacted.

I've attached a program that attempts to demonstrate this. Hopefully you'll find it minimal and easy to comprehend. Please let me know:

- Am I doing something wrong, and how?
- Is this a legitimate issue, and how might I work around it?


Please read the program description for the steps to reproduce the issue:

"""strange.py - demonstrating strange performane in Surface.blit

This program fills a screen with sprites to produce a checkerboard background,
and demonstrates a problem.

Controls:

  UP,DOWN,LEFT,RIGHT Âpan the background
  SPACE        center the background
  ESCAPE       Âquit

Reproducing the problem:

The times indicated in these steps are on a Intel i3 running Windows 7 64-bit.
Times will vary on other machines. The time cost measured is in blit ONLY.

1. Observe the cost per blit in the window's caption. On my machine it costs
 Âabout 0.0000015 seconds per blit.
2. Pan LEFT one or more pixels. Note the cost goes up nearly 4x (0.0000056).
3. Press SPACE to center the background. Note the cost goes back down to the
 Âoriginal value.
4. Pan RIGHT just one or more pixels. Note the costs goes up as in step 2.
5. Press SPACE to center the background.
6. Pan UP or DOWN: the cost is not impacted.
"""

Gumm

--

Diliup Gabadamudalige


http://www.diliupg.com
http://soft.diliupg.com/

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