Use for Reverse Graphics Mode?

RJBowman · Post by **RJBowman** » Sun Nov 27, 2011 9:33 pm

I was just looking up something that I remembered from back in the day; certain values in register 36879 resulted in all the text on the screen being displayed in inverse. I never found this feature to be of any use, and never used it for anything. This feature doesn't seem to work in the emulator on the main page of VIC20 Denial, so I thought that It might have been a product of bad human recall, so I looked it up.

So I found a PDF of the Programmer's reference guide, and found it. One bit in the background/border color register puts the screen into inverse mode when switched on.

I can think of one trick that you can do with this feature: you can fill the screen with spaces the same color as the background, then draw block patterns with spaces of another color. Then when you switch on the reverse mode, the block patterns appear. A crude trick, but maybe useful for something.

Is there a use for this feature that I haven't thought of?

GreyGhost · Post by **GreyGhost** » Thu Dec 01, 2011 7:11 am

You can use it to to make the text on the screen one of the high end colors (8-15). All of the text has to be one color unless a screen split is used. Just clear the screen and use {reverse on} with all the PRINT statements. IIRC.

Most likely everyone knew that one already.

Mike · Post by **Mike** » Thu Dec 01, 2011 7:42 am

The demo 'Ancient School' by sdw makes use of the inverse graphics mode in the dot, bob and vector parts.

Otherwise, this mode does not offer more capabilities than what could be achieved by working with inversed hires bit patterns within the character definitions in the first place (and it does not apply to multi-coloured characters!).

When a picture with inverse video is loaded into MINIPAINT, the first thing it does is recalculating the picture for normal video. The picture then still looks the same, but if MP wouldn't do that, such a picture would otherwise lead to an incorrect display of the editor user interface.

PhilRanger · Post by **PhilRanger** » Thu Dec 01, 2011 5:39 pm

GreyGhost wrote: All of the text has to be one color unless a screen split is used

What is a "split"?

Boray · Post by **Boray** » Thu Dec 01, 2011 6:04 pm

PhilRanger wrote:
GreyGhost wrote: All of the text has to be one color unless a screen split is used
What is a "split"?

Machine language is that fast that you can check where on the screen the TV beam is currently painting the picture and switch color, graphics mode, screen position or whatever in the middle of the screen. Here is for example a PAL program that changes the screen position to created a wave in the screen:
http://user.tninet.se/~pug510w/datormus ... sys828.prg

PhilRanger · Post by **PhilRanger** » Fri Dec 02, 2011 9:02 pm

Thanks, for a moment I dreamed it could have been a mode I didn't know!

TBCVIC · Post by **TBCVIC** » Thu Dec 08, 2011 5:02 am

I use reverse color for smooth scrolling vertically. I use a monochrome screen and use the screen positioning register to move the screen and a raster routine to hide the fact that the top and bottom border move.

You could make a game that scrolls freely in all directions with this technique, like a Sonic game. I've created a leveleditor for this:

http://sleepingelephant.com/ipw-web/bul ... php?t=4825