VGA snow...

[evildragon]

I'm trying to fade a screen on a program of mine.. Mainly, just doing what other programs that use VGA do, modify the screen with palettes of varying intensity (i think that's the right way to describe it)..

But, every time I do this, on my PS/2 with VGA, I get snow at the top of the screen... My Mac running a PC emulator doesn't have the snow, and neither does my modern PC with a GeForce graphics card...

So, what is with the real VGA cards and snowy pictures with palette changes?

I can re-produce this when playing the VGA/MCGA version of Wheel of Fortune, when it fades the logo and fade vanna whites picture, it has snow on the screen too..

 

[chuckcmagee]

I remember getting that long ago. Something to do with accessing the video ram while the card is accessing it too. I don't remember a lot of specifics.

 

[Thrashbarg]

http://www.geocities.com/SiliconValley/Park/8933/vga.html

there's a bit down the bottom about removing the snow.

 

[Mike Chambers]

yeah my old cirrus logic 8-bit VGA card in one of my XT clones gives pretty bad snow during palette changes too. it's very annoying.

 

[evildragon]

Ok, the code seems to work, but it slows down the palette change...

I guess I'll have to sacrifice the speed for no snow..

 

[Trixter]

Ok, the code seems to work, but it slows down the palette change...

I guess I'll have to sacrifice the speed for no snow..

Waiting for retrace limits your changes to 60Hz (480-line modes) or 70Hz (400-line modes). If your fade is slower, then increase the fade stepping (ie. decrease by 2 instead of 1).

This isn't really a big deal because the user isn't going to see more than 60 or 70 images a second anyway because of the screen refresh...

 

[evildragon]

im using 400 line mode (320x200).. I did end up doing just that to compensate it...