Character optical illusion

[kelp7]

Which is what I wondered. Wouldn't that effectively be 25fps ? Is 25fps not fast enough to fool the human eye?

[tlr]

Which is what I wondered. Wouldn't that effectively be 25fps ? Is 25fps not fast enough to fool the human eye?

Absolutely not.

Think of a flourescent light. That flickers at 100 Hz or 120 Hz depending on your country. (i.e both positive and negative half cycles) If you slow that down to 25 Hz it's going to flicker quite a bit.

[rhurst]

... and you all came back full circle to my first reply and suggestion that he just run Omega Fury for himself, as it does a proper VIC screen bank switch between screen update cycles to swap-out (any) two static characters (and sometimes colors) that occupy the same space:

1. Grenade mine is two green set of diamonds
2. Hull blaster is white skull alternating with purple cross
3. Sonic blaster are blue & cyan waves ((())), very nice effect
4. Heart stopper are simple red hearts, one smaller to look like its beating

So, yes, it FLICKERS. He wrote (flicker-free), which any one of us knows the (real) VIC screen flickers regardless.

Especially (full-speed) @ 30 fps for NTSC, 25 fps for PAL, best you can achieve. But as a cheap trick for animation or for getting two colors in "hi-res" mode, the "optical illusion" sought for "works" on a 1980s piece of hardware.

Or run this demo with +8K memory expansion and see the VIC graphic ball character (solid alternate with outline) effect on a later screen.

[kelp7]

Aha, I think I have all the understanding I need now Thanks everyone and sorry it was such a silly/basic question....!

[RJBowman]

Are you trying to switch back and forth rapidly to create a persistence-of-vision effect of two overlapping characters? If that is what you are trying to do, then the best bet is a raster-synchronized machine language subroutine that switches the characters thirty times per second. The result, if everything works perfectly, could be two semi-transparent characters superimposed into the same spot on the screen. Whether or not this produces flickers will depend on the persistence of the phosphors in your monitor.

[groepaz]

switches the characters thirty times per second.

better do that once per frame, ie 50(pal) or 60(ntsc) times per second

[RJBowman]

You might think that 60 FPS was the way to go if you didn't know about interlaced video. At sixty per second, some monitors will display an interlaced image, with each row of pixels split vertically, one character at the upper half of the row, the other character at the lower half of the row.

[groepaz]

unless you actually somehow make the VIC output an interlaced signal (that means shifting down every other frame half a line), no. if a monitor shows it the way you say, then its deinterlacer is broken

[darkatx]

Flicker Fusion frequency is 24 FPS/Hz or whatever.

The trick is in the changes themselves - if they're gradual then its seamless as in animation. Can people still detect flicker at that range? Well yeah, but it all depends on what you're trying to achieve.

[rhurst]

... but it all depends on what you're trying to achieve.

Well stated, enough said.

[tokra]

unless you actually somehow make the VIC output an interlaced signal (that means shifting down every other frame half a line), no. if a monitor shows it the way you say, then its deinterlacer is broken

Set bit 7 of $9000 - sadly VIC-6560 (NTSC) only

[kelp7]

Awesome replies all but not quite the original idea
Thanks though, I've realised by now it's not possible.

I wanted, as an example, to put the character 'A' on the screen at position x0,y0 in the first frame (out of the 50 frames), then in the 2nd frame, put character 'B' there in the same position, then swap back to 'A' in the 3rd frame, then swap to 'B' again in the 4th frame etc etc in the hope you could somehow make it look as if two display characters were occupying the same space on the screen...