is the author known?
is source available or only the binary?
is there a download link?

Question about Sierra's EGA640.DRV dithering

ripsaw8080 wrote on 2021-12-21, 17:34:

Question about Sierra's EGA640.DRV dithering

Thanks, that's definetly helpful. Would be interesting to understand the logic behind how the driver choses the colors and creates the dither patterns. But you would probably have to reverse engineer it.

FYI, some LucasArts adventure games offer the same kind of dithering with their "e" display option: Monkey Island 256-color, Monkey Island 2, Fate of Atlantis.

I have tried reverse engineering binaries. This is very time consuming and tedious. My advice would be to observe the driver's behaviour using a debugger. Perhaps a memory dumper or something that takes a snapshot of the current color palette.

i've reverse engineered the Stunts MT32 sound driver: https://github.com/LowLevelMahn/UnifiedMT15 - maybe its of help what tools are needed etc to get you started

ripsaw8080 wrote on 2021-12-22, 08:48:

FYI, some LucasArts adventure games offer the same kind of dithering with their "e" display option: Monkey Island 256-color, Monkey Island 2, Fate of Atlantis.

Yes... I found that out by accident... I had set DosBox zu EGA machine and started MI2. 😁 (You don't need the display option then)
Also Start Trek 25th Anniversary Edition seems to be able to do that as well but I have to buy that game first to try it out myself. 😀

https://retrocomputing.stackexchange.com/ques … games/8707#8707

Plasma wrote on 2021-12-22, 09:49:

https://retrocomputing.stackexchange.com/ques … games/8707#8707

Oh great, that's very helpful, thanks. 😀

I remember the 256-color versions of early LucasArts games (like Monkey Island 1) including a README that asked EGA owners to swap the game with the 16-color version if the dithering is too slow. And indeed, on a 12 MHz 286 computer with a slow (for today's standards) 8-bit VGA card, Indiana Jones and the Fate of Atlantis was updating the screen quite slowly if you forced it to EGA mode. Actually, I wonder how many machines were fast enough that the dithering wasn't annoyingly slow, but didn't support the VGA 256-color mode.

One of my friends played Monkey Island on a PCJr, back then annoyingly slow was considered par for the coarse

Look under the header "3C0-3CF EGA/VGA" at http://helppc.netcore2k.net/hardware/ports

That may contain some useful info, and at the risk of attention seeking self-advertising, possibly my Github page (see signature) will contain a few useful things. Probably nothing that will help with your immediate question but there is stuff about x86 assembly programming, memory dumping, screen dumping, and a Quick Basic program about video modes there.

PS:
I did a quick check of my games collection. It seems there several versions of EGA640.drv - I several of my games have a copy with a different size than the other.

Another PS:
Glancing with Microsoft Editor (it supports opening binary files) it seems each copy contains a header describing the driver followed by a repetitive data segment which is followed by a few kilobytes of varying binary values. Probably x86 machine code but don't hold me to it. The data segment looks like it could very well contain a color palette. Each version is approx 5-10kb in size.

Peter Swinkels wrote on 2021-12-22, 20:43:

PS:
I did a quick check of my games collection. It seems there several versions of EGA640.drv - I several of my games have a copy with a different size than the other.

table with some game names + sizes + MD5?

i've disassembed "Freddy Pharkas - Frontier Pharmacist\EGA640.DRV" with my IDA 6.8 (IDA Freeware 5 should give the same result): https://pastebin.com/NfeghyDy
is not that much assembler code - if one can read assembler 😀

I've found out that I could copy the EGA640.DRV from Space Quest 5 over to my Larry 5 and Police Quest 3 version that both didn't include it. The games run but unfortinaetly the mouse cursor is not showing anymore. So my guess would be that you need extra cursor images for EGA and those were only supplied when the game actually supported it? (I know there are Larry5 and PQ3 versions WITH ega support but mine don't have that unfortunately)
EcoQuest1 on the other hand worked even with mouse cursor when I copied the EGA640 file over. 😀

llm wrote on 2021-12-23, 06:01:

(IDA Freeware 5 should give the same result):

Just a hint: IDA Freeware 5 is obsolete. Currently, IDA Freeware is at 7.6, see https://hex-rays.com/ida-free/#download . For reverse-engineering 16-bit DOS stuff, IDA 5 should be good enough, or possibly even better, though.

mkarcher wrote on 2021-12-23, 07:08:

llm wrote on 2021-12-23, 06:01:

(IDA Freeware 5 should give the same result):

Just a hint: IDA Freeware 5 is obsolete. Currently, IDA Freeware is at 7.6, see https://hex-rays.com/ida-free/#download . For reverse-engineering 16-bit DOS stuff, IDA 5 should be good enough, or possibly even better, though.

i've got a full version IDA 7.6/Hex-rays at work so i know that there are new versions 😀 - my private license 6.8 is just a little bit older

the IDA Freeware 7 is very downsized - can't handle DOS exe/com or binary files - only Win PE executables - so it can't be used for most DOS reverse engineering stuff
Scummvm is now the official hoster of the old IDA 5 Freeware for that reason: https://www.scummvm.org/news/20180331/

but Ghidra (https://ghidra-sre.org/) is getting better and better - but still not on IDA level (compiler and library detection even for 1985 C compilers, Interrupt documentation etc. is just great with IDA) - Ghidra missing much of that

@ilm:

Peter Swinkels wrote on 2021-12-23, 09:15:

@ilm:
LLM not ilm 😀

can you post MD5 keys of the files: https://www.nirsoft.net/utils/hash_my_files.html (small util on command line or ui, no installation)