Setting Pixels Quickly

Question

I have searched and searched for a good answer and I am about to cry from frustration. I am a hobbyist programmer, I don't do things because they make sense, or they are the right way to do them; I do them to learn how, and right now I am stumped.

I want to set individual pixels on the screen. This may sound easy, but it's my other conditions that makes it hard. I need to do this quickly, CPU only, 20 fps or better (with other program elements running of course), on a 400 by 300 screen or better (full screen?).

I have been rendering some cool images using programs I wrote in Python that uses Pygame, but it takes 50 milliseconds to fill a 100px by 100px screen with just random pixels (that's my 20 fps right there, and other program bits slow it down more). Ideally I would LOVE to make my own (crappy) 3D game that just uses the CPU only, setting pixels on the screen (perhaps a voxel octree sort of graphics).

Is there any way (with any language, but preferably Python) I could like, make a 2D array of pixel values (more like 3D array with RGB) (is this called a bitmap?) in the RAM and dump it on to the display or something? Wouldn't that be fast??? How DO you interface directly with the pixels on a window. Argh! I am so clueless. I am / am not a programming noob. Give me whatever you can throw at me, I can digest it. I just need some pointers (haha) in the right direction.

Answer 1

If you want to make your own "for each pixel" math (as opposed to just moving circles and bitmaps around), you will have to do it in C (or C++) to get anywhere close to machine speed.

On the other hand, if you want to make a full game, it will not be fun to write it all in a low-level language like C. You will need to combine fast C code with some some high-level scripting language. With Python you can bridge to a C extension module via numpy, or you can embed a language like Lua into C code, or you can try (oh horror) to learn high-level coding in C++. Either way things will get complex.

If you just want to play around with fast pixel rendering, I reccommend to use SDL (that's what pygame uses internally) but with C or C++ only. Follow a tutorial like this one and have some fun.

If you want to stay within the comfort of Python, I suggest you try a 2D game first (loading and moving around bitmaps) or experiment with cairo (render geometric shapes).

Answer 2

I'm able to get over 20 fps at a resolution of (1920,1080) with pygame.

As Mallett pointed out, you should be using the pygame.surfarray.blit_array() function to copy the pixel data to pygame, and then update the screen with a call to pygame.display.flip().

>>> import timeit
>>> timeit.timeit('pygame.surfarray.blit_array(screen, pixels);pygame.display.flip()', setup='import pygame;import numpy as np;size=(1920,1080);screen=pygame.display.set_mode(size);pixels=np.random.randint(np.iinfo(np.uint32).max,size=size).astype(np.uint32)', number=20)
0.6346819400787354
>>> timeit.timeit("""
... pygame.surfarray.blit_array(screen, pixels)
... pygame.display.flip()
... """,setup="""
... import pygame
... import numpy as np
... size=(1920,1080)
... screen=pygame.display.set_mode(size)
... pixels=np.random.randint(np.iinfo(np.uint32).max,size=size).astype(np.uint32)
... """, number=20)
0.4848361015319824