Monday, July 18, 2016

Video Potpourri

I am going to discuss a pair of video topics in this post which do not by themselves merit full blog entries on their own.  Each discussion will have a link to a Youtube video demonstrating the topic discussed.

I.  Hercules Graphics Tidbits

Someone remarked on the VOGONS forum that certain 16-color LucasArts SCUMM games, Indiana Jones and the Last Crusade: The Adventure Game and LOOM, do not support Hercules Graphics.  Earlier SCUMM games, Maniac Mansion and Zak McKracken and the Alien Mindbenders support Hercules Graphics in both their original and Enhanced releases.  The Secret of Monkey Island, which came immediately after LOOM, also supports Hercules Graphics in its original 16-color release.




Around this time, LucasArts released a demo called "Passport to Adventure."  While computer game companies had released demonstration programs in the past, they were rarely interactive.  Instead, they functioned more like trailers for the game.  There is a non-interactive demo for Maniac Mansion.  Sierra Online also released non-interactive demonstration programs advertising their games and to be run on floor model systems to show off their advanced graphics and sound.  Unlike these earlier programs, Passport to Adventure contained interactive sequences from three of LucasArts' games, Indy 3, Loom and Monkey Island.  LucasArts also called this a sampler disk and only a 16-color version was made available.

Ironically, the sampler disk does support Hercules graphics for Loom and Indy 3 whereas the full games do not.  Both games can be run with a CGA emulator like SIMCGA with reasonable results.  Compare the following screens :

Loom - SIMCGA Hercules Support

Loom - Passport to Adventure Native Hercules Support
SIMCGA adjusts the CRTC registers for a 640x300 resolution, which is close to the native resolution of these graphics, 320x200.  The native Hercules driver does not touch the CRTC registers, instead it uses the ordinary Hercules Graphics resolution of 720x348.  The native driver only uses the center 640 pixels, but uses more lines in the vertical dimension than SIMCGA.

Loom - SIMCGA IBM 5151
Loom - Passport to Adventure IBM 5151
When you start the demo on a Hercules card, a neat effect occurs.  View the video here :



The LucasFilm Games logo is just drawn to the screen.  The consequence of changing from text to graphics mode combined with the slow, long persistence phosphors gives the effect.  No other display will show this.

An unintentional effect of changing from text to graphics mode when you start this demo. The system used is a Tandy 1000 TL, and it emulates the Hercules card very well. Unfortunately many games tend to freak out when they detect a Tandy 1000 and default to the Tandy 1000 graphics modes or fail to restore the Hercules mode when you quit. This tends to cause the sync issues shown at the beginning of this video.  It is best to always an install option or command line argument to designate the Hercules mode when running on a Tandy that supports Hercules.

II.  The Sega Master System's Composite Effect

The Sega Master System's  RF and Composite output is a tad fuzzy compared to its main competitor the Nintendo Entertainment System.  On the rare occasion where a NES game will show alternating colums of 1-pixel wide colors, you will see 1-pixel wide columns.  A good example of where this occurs is in the NES release of Spy vs. Spy.  You will notice with the NES that alternating borders of colors other than black and white tend to have a 3-line staircase effect.  A good example are the inventory boxes in The Legend of Zelda.  This staircase effect and the fact that the graphics shift by 1 pixel each frame is essentially the reason why you see striped graphics in games like Spy vs. Spy.

In the Sega Master System version of Shinobi, levels 2-1 and 2-3 have warehouse buildings in the background.  They look like this through the RGB output :


But the Master System does not show staircase lines with composite, it shows straight lines.  The system, like the NES, uses a 5.37MHz dot clock.  Neither system shows true artifact color, which tends to be reliable only when the dot clock is a multiple of the NTSC color clock 3.58MHz.  There still something of a noticeable color bleed effect to the Master System because it does not shift each line by 1/3 of a pixel or shift the graphics by 1-pixel each frame like the NES does.

As a consequence, you will see this when you play Shinobi on a Master System or Genesis through composite video :



No other video on Youtube even comes close to displaying this effect correctly, and no SMS emulator does either.  The NTSC filter in Kega Fusion merely smooths the lines out into an average color, which as you can see is far from what was intended.

1 comment:

Dr. Zeissler said...

SIMCGA produces a good quality but it's so slow, only a very view amount of games can be played on a slow xt with hercules gfx and simcga for playing the cga-only titles.