Free Sprites

[erico]

hehe you guys are playing too much custer´s revenge...it is just a bunch of pixels.
On attempt to change topic...the gamebuino in the dark looks cool with all those leds.

[Myndale]

@Draker: you got it!



I switched to a fixed-frequency interrupt-driven refresh this morning and the magic number for eliminating flicker seems to be somewhere around 41FPS, it can probably be improved with more accurate timer code. The hatch pattern helps a lot with static images but it becomes really noticeable once you add animation, so it's gone in that video. Grey flicker is worse in the video than it is to the eye, if you look closely you'll see the black is flickering a bit as well. One thing that is obvious is that it appears to be closely related to ambient light levels...more obvious under bright lamp light, practically invisible under LED illumination.

I think one of the biggest challenges with grey-scale games will be the RAM requirements. The obvious method of 2 bits per pixel (which I'm currently using) requires two frame buffers for a total of 1008 bytes i.e. almost half of available RAM. An optimal pixel format would require exactly 799 bytes (i.e. log(3^(84*48))/log(2)/8) but it would be impossible to work with. What might be a good compromise is to pack 5 grey-scale pixels per byte (3^5=243). Reserve the top (or bottom) 4 lines for a static area to display score etc and you would then only need 9 bytes per column i.e. a total buffer size of 756 bytes.

[erico]

Interesting xperimentation.
Flicker by ambient light is probably related to light type frequencies (in my naive opinion) it happens not only to screens but paper and bright surfaces.

I take you are scrolling 1 pixel per frame on ~20.5fps? looks like half of it?

[Myndale]

Yes, that's correct. I render each of the two frames for every pixel I scroll.

[Drakker]

Wow, that looks very good! Guess I'm sold on the idea of using grayscale.

Wouldn't using 2 bits sprites with a conditional be better for displaying gray? Say, when the frame is even, gray is drawn as black, and when the frame is odd, gray is drawn as white. This could be easily implemented in a simple wrapper function that puts the sprites on the screen. In a scheme like this:
0 = transparency
1 = white
2 = gray
3 = black

[Myndale]

I think Erico might be right about the flicker, I just filmed it again using ambient indoor daylight and with a much better quality camera and at hi-res the video looks exactly as it looks to my eye:



@Draker: that would be a good format for sprites, I was thinking more about full-screen scrolling backgrounds that would never need alpha.

[Drakker]

@Myndale: oh, true. Well, what's been done on moon patrol for some platform is that the game starts with 3 bands of color, black for the star field and for the far blue mountains, yellowish for close mountains and brown for ground. Afterward, they draw only details on there, say, mountains shapes and shadows, holes in the ground and rocks that need to be shot. Then, once this is done, they draw the vehicles, projectiles and enemy ships.

This can be seen in this video: https://www.youtube.com/watch?v=uyPZwuynMFA

Maybe something similar could be done on the Gamebuino with black/gray/white.

[erico]

That video has one of the best explosions I have ever seen, when enemy bullets hit ground.
...
Great video Myndale!

[erico]

I have to add, that the speed Myndale is scrolling is quite xtreme for that kind of game
Superb test!

Suppose on that moon patrol mock, we are probably going to scroll the foreground about half of that speed? Maybe only main sprite and enemies move that fast, and that is if.

And background, just a slice of screen at about 1/8 of speed.

Really great to see live videos of Gamebuino.

[DFX2KX]

I think Erico might be right about the flicker, I just filmed it again using ambient indoor daylight and with a much better quality camera and at hi-res the video looks exactly as it looks to my eye:

@Draker: that would be a good format for sprites, I was thinking more about full-screen scrolling backgrounds that would never need alpha.

That came out surprisingly good! The blur is a lot better then the TI-8x monitor was.