Invert LCD screen in DOS 5.0

Question

Would like to run "black on white" software on a DOS machine with an LCD screen, so am wondering if there are any TSR tools, or similar, for inverting the screen. I believe it is grey scale VGA, not monochrome.

It's a HP Omnibook 300, if that matters.

I had a look at Simtel (I believe) a while ago, but could not find anything that worked.

Addition: I am running DOS only, not MS Windows.

More additions: ansi.sys does not seem to work, I believe the program handles the graphics directly by itself. The program also does not have a way to change the colours. Giving the command mode mono before running the program does not make a difference to the program (but it does mess up the display of the battery level, which is something special apparently using the CP437/850 block graphics). The machine does not have any BIOS options for changing the display in any way. In fact I am not sure it even has a standard BIOS.

Answer 1

You can invert the screen on a monochrome Omnibook by holding the Fn key and pressing either of the contrast up/down buttons next to the screen.

Answer 2

Some laptops have built-in support for inverting the screen in one form or another; Toshiba laptops for instance have a setup menu to configure gray-scale translation and inversion, as well as a pop-up TSR and a command-line tool (VCHAD on VGA systems). If your system doesn’t have anything like this, I think your options are rather limited...

As mentioned by RichF, ANSI.SYS will allow you to set the current foreground and background colours, which will work for programs which don’t reset them; in practice, that’s mostly the DOS prompt and console tools, most full-screen programs will reset the colours themselves. If you do want to explore this option, I recommend using a more capable driver such as NNANSI, along with ANSISET to set things up more easily.

Other options you could look at are the basic MODE MONO, which will switch the system to monochrome mode, and perhaps the PC Magazine TSR MONO which will replace text-mode character attributes continuously with monochrome attributes, and which you can modify to choose your own replacement colours. If you can find a copy somewhere, UltraVision should provide enough control to set things up however you want — that was the go-to utility for DOS laptop users in the nineties (this was developed by Personics, and last released as “Laptop UltraVision”).

Many DOS programs also support colour configuration of their own, some with pre-configured palettes for various types of LCD screens.

Answer 3

Seems to me that the way to go would be to re-program the lookup table use by the digital to analog converter (DAC).

The DAC is essentially the last component in the VGA, taking 8-bit VGA colors and deciding what each of those will represent. Thus, it affects the output from essentially all other programs, even those that write directly to the hardware. The only obvious exception would be programs that themselves re-program the same lookup table--not really much you can do about that.

For programs that run in text mode and/or high-resolution graphics (640x480), you only need to worry about the first 16 entries in the LUT (because they only use 16 colors, of course). In this case, you can read the current values from the LUT, invert their order (swap 0 and 15, 1 and 14, etc.) and then write them back to the LUT. The first 16 colors are (at least normally) chosen so that inverting the color number approximately inverts the color itself (e.g., 0->black, 15->white, 1->blue, 14->yellow, etc.)

As to a pre-existing program to do this...sorry, but I don't know of one. The code to handle this really is fairly simple though. I'd be tempted to write it and post the source code, but I wouldn't be able to test it...

References:

1. http://www.osdever.net/FreeVGA/vga/vgadac.htm
2. https://en.wikipedia.org/wiki/Video_Graphics_Array#Color_palette

Answer 4

For programs which run within a DOS screen or window, you should be able to pre-load ANSI.SYS with CONFIG.SYS. You would then preset your desired foreground and background colors before running the program you wanted. The page ANSI Sequences seems to give pretty good guidance in using ANSI within a DOS window.

I'm not sure whether ANSI.SYS still came standard with MS-DOS 5.0. It would still work, but for some reason they removed it from the standard distribution at some point.

Answer 5

If all else fails, and you're up for (or know somebody who would be interested in) a fun low-level programming challenge, there's an interesting hack you could apply to this problem. This will work if:

• the software you want to run is traditional real-mode text-mode DOS software (i.e. doesn't use DPMI or similar), and
• you have a 386 or higher processor (which I believe you do in the machine you describe) and a bit of spare extended memory space.

The way it would work is to use the 386's Virtual X86 mode to map some extended memory into the space usually occupied by the text display; you would then map the original location somewhere else (probably outside of the lower 1MB address range) and run a periodic operation to copy the data from one to the other, flipping attributes while you did.

This isn't an easy task, but it may be easier than expected because there are open source 386 Expanded Memory Manager implementations available which already do a lot of the necessary work.

Of course, it would probably be better to solve this in just about any other way you can think of. But this way would be fun. :)