How CGA Graphics worked [video] | Hacker News Reader

How CGA Graphics worked [video]

youtube.com

90 pointsJerry219 comments

This wouldn't be complete without mentioning the enhanced CGA version a lot of Europeans experienced via Amstrad/Schneider PCs in the 80s (they tended to be the cheapest way to get a PC here, back then).

"The Amstrad used an "enhanced" CGA graphic mode, which could display 640x200 pixels with 16 colors (or grayscale)."

http://www.old-computers.com/museum/computer.asp?c=183&st=1

http://www.nostalgianerd.com/amstrad-pc1512

There were probably at least five pieces of software released which supported this mode. :)

The PC1512 came bundled with the GEM windowing system from Digital Research, including a paint program: http://www.reenigne.org/computer/gempaint.gif as well as a fairly state of the art graphical BASIC: http://www.reenigne.org/computer/basic2.gif, https://www.youtube.com/watch?v=dDL8w_Mi49A (video in EGA though).

I had one and I learnt low-level programming on it. I recall my befuddled confusion when my stuff looked totally glitched on other ‘CGA’ machines.

Ah GEM and Basic 2 Plus! My parents wrote a retail system (cashier, stock, orders) for their store with this and it's still running today (via DOSBox, the hardware is long gone)

The Japanese made numerous PCs in the 1980s that all had different graphics systems. I went to Japan in 1987 to help a company get their graphics software to run on all those systems.

That BASIC looks way ahead of it's time. Thanks so much for sharing.

The PC1512 was the computers we had on the PC room on high school.

I did spent a few hours playing "Defender of the Crown" on them.

https://www.youtube.com/watch?v=x7fAaUq1H2k

This link is dead.

I assume this is the same video.

https://www.youtube.com/watch?v=niKblgZupOc

Speaking of CGA... did you know that an IBM PC 5150 (4.77 MHz Intel 8088) with a CGA card can display full framerate video?

http://trixter.oldskool.org/2014/06/19/8088-domination-post-...

This is accomplished by compiling the video into branch-free code that sends minimal updates to the CGA.

The same demogroup did this around a year later:

https://news.ycombinator.com/item?id=9338944

http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-m...

I often thought that CGA could have been much better with very little change at the hardware level.

If the colour displayed onscreen had the red level inverted the options would have been much more erm... palatable.

For an output of (1-r,g,b) you would get some lovely options http://i.imgur.com/rMAr9mU.png

If done at the Digital level flipping the R line of the RGBI You would remain in the standard 16 colours but with better combinations

http://i.imgur.com/2AWs9E7.png

You get a nice blue gradient palette and an earth tone palette (brown,black and green).

Yes but wouldn't 16 colors in composite mode look worse then?

It seems like these colors were chosen exactly because when you mixed them you would get nicer colors.

The video is a bit misleading here - most CGA composite games didn't use the 2bpp mode at all but instead used the 1bpp mode. This gave 15 reasonably nice colours distributed roughly evenly through RGB space, and was also more consistent between different versions of the CGA card.

Whole RGBI output was a big mistake imo, monitors internally have fully analog RGB path, so why not use it?

Imagine if CGA cards had full palette control from the start. Four 74189 16x4 bit SRAM chips connected to R2R resistor ladder providing programmable 5-6-5 RGB palette. Would add ~$30 to the BOM in 1981, but SRAM prices fell drastically at that time, two years later it would be single dollars.

TIL: dosbox can emulate CGA composite mode.

Of course, Hercules Graphics Adapter is the one true graphics adapter :-)

CGA 4-color mode was extra "fun" after SIMCGA munged it to black and white pixels with a different aspect ratio.

Great video, but missing from the palette discussion is the cyan-red-grey option, which was by far the best one and only used in a handful of games.

Be sure to check out the game Round 42 for another great demonstration of the 160x100x16 mode.

I had access to that Tandy portable - it had the WORST screen ever, but for some reason I have a soft spot for it.

Round 42! What a blast from the past. I don't know how well-known that game is, but when it ran (on our IBM PCjr with the memory expansion), it was great fun and a graphical treat (for the time).

Another Round 42 fan here from way back. This was one of the first of original PC games to start failing on newer hardware; even most VGA cards weren't compatible with that funky CGA mode. I wonder if Dosbox can handle it at all...

cyan-red-grey was the composite output mode, and I agree it was FTW.

I also liked 2-scanlines-per-character text modes used to hack up graphics modes

Reply on news.ycombinator.com