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Old 03 August 2017, 20:59   #1
Sim085
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Just curious; Graphics Card

Hello, I like to go through the Amiga Hardware database and read about past models. However I always wondered what was the use of Graphics Card with the Amiga?

I know the Amiga had OCS, ECS and AGA graphics; so what did a graphics card give to an Amiga? Was it used to see photos and videos on the amiga?

Also if you go to Amiga Hardware you see multiple categories; 3D graphics, RTG graphics, Graphics Expansions ... what is the difference between these?

Apologies if these questions seems newb; I mostly know Graphics Card from the PC world. For me OCS, ECS and AGA are like the on-bourd gpu on a pc motherboard and a graphics card provides extra functionality over this. For me the most important extra thing would have been seeing photos in full colour so that is why I am linking that to this.
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Old 03 August 2017, 21:07   #2
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It's not that complicated, most graphics cards simply gave the Amiga VGA capabilities similar to how it worked on PCs. A few of the last models had rudimentary 3D features as well. There were some exotic things like the Graffiti card which generated a multi-colour mode in conjunction with the native chipset.

Graphics cards could be used with most system legal software, i.e. productivity stuff, but were largely incompatible with games which directly accessed the native chipset. Some PC ports like Doom, Quake and others were able to take advantage of graphics cards including 3D capabilities.
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Old 03 August 2017, 23:40   #3
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So all graphics card provided a VGA output which was separate from the normal Amiga output?
Would a game in AGA still be playable when using a graphics card?
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Old 03 August 2017, 23:57   #4
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Generally you swap to AGA output when the game is run. Some cards handle this themselves, otherwise you need a switcher to flip between the graphics card and the native output.
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Old 04 August 2017, 00:27   #5
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RTG cards are typically what the above people are taking about, it is like a video card in a PCI slot in a PC and they often used a GFX chip from a PC Video card, like an S3 Trio or a Cirrus Logic chip. The AmigaOS didn't support these cards natively so RTG software was created along with these cards, CybergraphX and Picasso96 and others. So your Workbench and system friendly applications would display on the RTG card but your floppy based games would not. Most of these RTG cards had a built in video switcher so your Amiga chipset output would go to this card and automatically switch between the two.

The other graphics cards which were not RTG were mostly 24-bit framebuffers which were not system-friendly and mostly only worked with whatever software was sold with the card, some of which were capable of Animation and usually included some kind of paint program and a picture viewer. These were mainly before the RTG solutions existed.

Then you had all of the video cards which weren't video cards but video processor cards which fall into the everything else category, you have capture cards, Time base correctors, and all of the miscellaneous stuff you needed edit, capture, mix or output to tape back in the day. Lets say Genlocks fall into this category too.
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Old 04 August 2017, 09:41   #6
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@Sim085

Graphics cards don't stop an OCS/AGA game from running, but how well the VGA output co-exists with the native output depends on the card. Some, such as the PicassoIV, have a built-in scandoubler which makes the native modes VGA compatible. Some have a pass-through, so that the native modes are transmitted via the same cable but the monitor has to be multi-sync in order to display them. And some do not have any support for the native signal at all, so you need to switch between them manually (or use two monitors).

RTG stands for "retargetable graphics", essentially meaning that software is not locked to using any particular graphics chipset. It will run on anything you have a driver for. You can even use AGA as a "graphics card" via RTG, although this is quite slow and isn't commonly done.

Here's a video of mine from some years ago, showing a 1024x768 24-bit Workbench, but also running older games through an IndivisionAGA and a monitor switcher:

[ Show youtube player ]
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Old 04 August 2017, 10:51   #7
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Indeed, and if you do any sort of productivity work on your Amiga, once you've used a graphics card, it's extremely difficult to go back. Full 24-bit colour, high resolutions and faster updating than AGA could ever handle, and not to mention no dependency on chip RAM any more, all make it a far more pleasant (and dare I say it, "modern") experience. With my A1200 fitted with a Voodoo 3 I can just about squeeze out a 1920x1200 Workbench screen, the native resolution of my monitor.

There are a small number of Amiga games that can take advantage of graphics cards too, such as Payback, Foundation, Napalm and Genetic Species as well as a bunch of PC ports (Doom, Quake, Heretic II, Earth 2140, Descent: Freespace, Shogo: MAD, Wipeout...) Playing these games on a graphics card is a world of difference from AGA (especially those that take advantage of 3D acceleration), and many simply won't work at all without a graphics card.
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Old 04 August 2017, 11:55   #8
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So in general, they were good for productivity work, but not enough games supported them if you were just buying them for games, esp without hardware acceleration.
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Old 04 August 2017, 12:37   #9
Sim085
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So for example what is the difference between these two:
http://amiga.resource.cx/exp/indivisionagamk2
http://amiga.resource.cx/exp/blizzardvision

One is marked as an RTG card and the other as a Flicker Fixer.
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Old 04 August 2017, 12:38   #10
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@Amigajay

Yeah, most graphics cards appeared relatively late in the Amiga history. Had there been official support from Commodore starting from the A2000, things might have been different. Although even so, being expensive items, they would probably never have been common among the large majority who just wanted a cheap games machine. Certainly games like Sim City, Settlers and many others could have benefited from having a large resolution option available.

@Sim085

The BlizzardVisionPPC provides a proper VGA/3D chipset (Permedia 2) and 8MB of video RAM, while the Indivision just converts AGA to VGA in order to display it on modern monitors better.
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Old 04 August 2017, 14:49   #11
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Quote:
Originally Posted by Sim085 View Post
So for example what is the difference between these two:
http://amiga.resource.cx/exp/indivisionagamk2
http://amiga.resource.cx/exp/blizzardvision

One is marked as an RTG card and the other as a Flicker Fixer.
I don't want to sound rude, but difference is obivous. Indivision just enables normat VGA monitors for Amiga and removers flicker hires interlace screens. It still plain AGA chipset.
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Old 04 August 2017, 17:55   #12
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Yes apologies, I was confused by this line "24 bit color support (16.7 million colors)". Am I correct that with Indivision photo quality would be the same as normal AGA, while with an RTG card it would better?

Quote:
Originally Posted by utri007 View Post
I don't want to sound rude, but difference is obivous. Indivision just enables normat VGA monitors for Amiga and removers flicker hires interlace screens. It still plain AGA chipset.
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Old 04 August 2017, 18:24   #13
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AGA has a 24-bit colour palette, but the best it can do for a single screen mode is HAM8 - with or without an Indivision. So yes, there is no impact on the image quality in that sense.

Some older scandoublers actually reduced the image to something like a 12- or 16-bit palette so that's probably why its mentioned.
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Old 04 August 2017, 18:37   #14
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Quote:
Originally Posted by Sim085 View Post
Yes apologies, I was confused by this line "24 bit color support (16.7 million colors)". Am I correct that with Indivision photo quality would be the same as normal AGA, while with an RTG card it would better?
Well, hardware-wise, the Indivision has a frame buffer and Grafitti support which is a kind of graphics card, but I don't think any software was ever implemented to enable this feature on the Indivision AGA, so those specs are a bit of a stretch. With the Indivision ECS, there was a tool included which could display still pictures (jpg etc) in 24 bit colors using this special feature. It could not be used for WB though.

You could argue that AGA in itself can also do 16.7 mill. colors. That is how they marketed the A1200 back in 92.
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Old 04 August 2017, 18:40   #15
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In short, RTG graphics cards can display higher resolutions and more colors than the native chipset. e.g., you can get a 1024x768 256-color display on an A2000, which is not possible natively. But programs need to support one of the RTG standards (CGX, P96) in order to use one of those screenmodes. Most games do not. The exceptions mentioned earlier are all games from the late 90s, once RTG graphics cards were more common.

Scandoublers/FlickerFixers simply modify the output frequencies of the native chipset so that they can be displayed on VGA monitors. Generally speaking, at most, they can only replicate the features and color modes of the native chipset.* The Indivision AGA makes specific note of 24 bit color support because that corresponds to the HAM8 screenmode. In contrast, some older scandoublers don't support every feature of the native chipset and can only handle the basic screenmodes, up to 256 colors, and maybe HAM6 (4096 colors). This was likely a cost saving measure in the design (or in some cases because the AGA chipset didn't exist yet) and was often deemed an acceptable tradeoff because the unsupported modes are so rarely used. For example, Super Hi-Res (1280x400/512) was usually meant for video titling rather than every day use, and if you were doing video titling you probably had a monitor that didn't require a scandoubler.

* Although the Indivision adds a few extra options as well.
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Old 05 August 2017, 16:03   #16
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Indivision is special case where native chipset was reimplemented in FPGA and can be considered as natural extension for chipset (it can interpret differently than chipset data from internal memory where flicker fixers or extensions like Graffiti only interpret display data from chipset).

Side to this plenty of games on PC (before introducing VESA API or WinGDI or DirectX) provided dedicated software drivers for graphic cards and was able to run from DOS only (required direct access to hardware and Windows before Windows 95 was to limited and to slow).

Amiga situation was quite complicated as popular models used mostly for entertainment (games) was practically unfeasible to made additional graphic boards and 'large' Amigas rather unpopular as gaming machines.

Side to all above it was extremally difficult as graphic controllers IC's population was very limited - practically only few, quite modern with some blitter, line drawing and decently fast existed those times, relatively expensive as RAM + GDC/GDP cost was very high - solutions as TMS34010/34020, some HD63484 http://www.vgamuseum.info/index.php/...-hd63484-acrtc, some Motorola controllers (not the ancient 6845) was available with some literature but usually Amiga custom chips delivered very similar functionality and performance (fastest those times IBM accelerated display card was PGC model using as graphic processor normal CPU 8088 was slower than OCS IMHO, offered less than AGA and cost 4000$ in 1984).
High quality graphics HW and SW was very expensive (hundreds k$) and usually area for company like Silicone Graphics, Evans&Sutherland, required dozen large custom VLSI chips...
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Old 08 August 2017, 09:54   #17
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So I went back and did some reading. With regards to AGA I found the following:

Quote:
"This allows for 256 colors in indexed display modes and 262,144 colors (18-bit) in Hold-And-Modify (HAM-8) modes. The palette for the AGA chipset has 256 entries from 16,777,216 colors (24-bit)"
You can select between 16,777,216 different colours but can only display 262,144 different colors at the same time.

Am I understanding this correctly?
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Old 08 August 2017, 10:36   #18
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Quote:
Originally Posted by Sim085 View Post
So I went back and did some reading. With regards to AGA I found the following:

You can select between 16,777,216 different colours but can only display 262,144 different colors at the same time.

Am I understanding this correctly?
Depends on the graphics mode. AGA can display 262k colours in HAM8 mode, but like HAM on earlier Amigas, that mode was very limited and not used for much beyond slideshows (probably lots of stuff in the demo-scene as well but I was never into demos). In most usable modes, you're looking at a maximum of 256 colours.

AGA was rushed out by Commodore as a half-arsed attempt at bringing the Amiga graphics up-to-date after years of neglect. A graphics card is more powerful - it will give you usable true-colour modes and higher resolutions, things that the PC world was beginning to enjoy at the time.
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Old 08 August 2017, 10:46   #19
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Yep, and you need to be aware of the difference between a 24-bit palette and a 24-bit depth of screenmode. The palette just means colours can be chosen from 16.7 million possibilities, with 8 bits for red, 8 bits for green and 8 bits for blue. AGA has this in all modes, but (HAM excluded) can only use up to 256 of these 24-bit colours at any one time due to the display only being 8 bits deep. The display depth is what defines how many individually coloured pixels you can have on screen. If your display is 1 bit deep you can display 2 colours, 4 bits deep, you can display 16 colours, etc. AGA maxes out at 8 bits deep, whereas graphics cards are typically 24 bits deep as well as a 24 bit palette, meaning every pixel on the screen can be a different colour.
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Old 16 August 2017, 05:14   #20
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Quote:
Originally Posted by Sim085 View Post
So I went back and did some reading. With regards to AGA I found the following:



You can select between 16,777,216 different colours but can only display 262,144 different colors at the same time.

Am I understanding this correctly?
Yes you are understanding this correctly, a HAM-8 picture can have that many colors, you can play HAM-8 animations with that many colors and so on. However due to limitations in Chip RAM bandwidth (Amiga VRAM bandwidth) playing animations higher much higher resolution than 384x240@30FPS will stutter as it's not fast enough.

Not many applications used HAM-8 modes, no games that I can think of but there are hacks to use the Workbench in HAM-8 mode, which I've never used. Some other random programs will use it like Shapeshifter (a Mac emulator) if you use the video drivers intended for that. Paint and graphics programs regularly used HAM-8 modes.
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