5 ms·

How CGA Graphics worked [video]

90 points by Jerry2 11y ago

brandonmenc 11y ago
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.
- mysterydip 11y ago
  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).
  - T-hawk 11y ago
    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...
- thanatos519 11y ago
  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
rwmj 11y ago
TIL: dosbox can emulate CGA composite mode. Of course, Hercules Graphics Adapter is the one true graphics adapter :-)
- pdkl95 11y ago
  CGA 4-color mode was extra "fun" after SIMCGA munged it to black and white pixels with a different aspect ratio.
adrusi 11y ago
This link is dead. I assume this is the same video. https://www.youtube.com/watch?v=niKblgZupOc https://www.youtube.com/watch?v=niKblgZupOc
johansch 11y ago
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.old-computers.com/museum/computer.asp?c=183&st=1 http://www.nostalgianerd.com/amstrad-pc1512 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 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 http://www.reenigne.org/computer/basic2.gif, https://www.youtube.com/watch?v=dDL8w_Mi49A https://www.youtube.com/watch?v=dDL8w_Mi49A (video in EGA though).
- qubex 11y ago
  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.
- songshu 11y ago
  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)
- WalterBright 11y ago
  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.
- Timethy 11y ago
  That BASIC looks way ahead of it's time. Thanks so much for sharing.
- pjmlp 11y ago
  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 https://www.youtube.com/watch?v=x7fAaUq1H2k
Lerc 11y ago
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 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 http://i.imgur.com/2AWs9E7.png You get a nice blue gradient palette and an earth tone palette (brown,black and green).
- takeda 11y ago
  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.
  - ajenner 11y ago
    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.
- rasz_pl 11y ago
  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.
- deleted 11y ago
  [deleted]
pdkl95 11y ago
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-mortem-part-1/ 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.
- userbinator 11y ago
  The same demogroup did this around a year later: https://news.ycombinator.com/item?id=9338944 https://news.ycombinator.com/item?id=9338944 http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-mode-illustrated.html http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-m...

90 points by Jerry2 11y ago

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.

mysterydip 11y ago
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).
- T-hawk 11y ago
  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...
thanatos519 11y ago
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

rwmj 11y ago

TIL: dosbox can emulate CGA composite mode. Of course, Hercules Graphics Adapter is the one true graphics adapter :-)

pdkl95 11y ago
CGA 4-color mode was extra "fun" after SIMCGA munged it to black and white pixels with a different aspect ratio.

adrusi 11y ago

This link is dead. I assume this is the same video. https://www.youtube.com/watch?v=niKblgZupOc https://www.youtube.com/watch?v=niKblgZupOc

johansch 11y ago

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.old-computers.com/museum/computer.asp?c=183&st=1 http://www.nostalgianerd.com/amstrad-pc1512 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 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 http://www.reenigne.org/computer/basic2.gif, https://www.youtube.com/watch?v=dDL8w_Mi49A https://www.youtube.com/watch?v=dDL8w_Mi49A (video in EGA though).

qubex 11y ago
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.
songshu 11y ago
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)
WalterBright 11y ago
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.
Timethy 11y ago
That BASIC looks way ahead of it's time. Thanks so much for sharing.
pjmlp 11y ago
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 https://www.youtube.com/watch?v=x7fAaUq1H2k

Lerc 11y ago

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 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 http://i.imgur.com/2AWs9E7.png You get a nice blue gradient palette and an earth tone palette (brown,black and green).

takeda 11y ago
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.
- ajenner 11y ago
  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.
rasz_pl 11y ago
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.
deleted 11y ago
[deleted]

pdkl95 11y ago

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-mortem-part-1/ 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.

userbinator 11y ago
The same demogroup did this around a year later: https://news.ycombinator.com/item?id=9338944 https://news.ycombinator.com/item?id=9338944 http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-mode-illustrated.html http://8088mph.blogspot.com/2015/04/cga-in-1024-colors-new-m...