14 March 2019, 13:17 | #1 |
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Missing Display modes
My question here is, what display modes the Amiga Chipset is missing.
In the sense of: what could have been implemented back than without much trouble/changes to the rest of the design and could be provided now by an emulator or FPGA. (I know: this is probably not useful and the Amiga is what it is - this is just a thought experiment.) My Ideas:
your ideas? |
14 March 2019, 13:38 | #2 |
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I'd have liked a better range of resolutions available for 15khz displays. 640x480, 800x600, etc. AGA should have done this.
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14 March 2019, 13:40 | #3 |
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14 March 2019, 13:46 | #4 |
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Really, once Commodore we’re using the faster dram chips for chipram (the ECS chipset), it became realistic to fetch a byte of data per pixel (hence 8bitplane mode of AGA), it was ridiculous that the chipset didn’t include a 256 colour chunky mode. This is the biggest omission from the chipset, and that should have been present around ‘88 or ‘89.
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14 March 2019, 13:49 | #5 | |
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you could do that in theory - but 15kHz is the result of the horizontal refresh rate (50/60 Hz) and the number of lines. So 600 lines would give you 15.000/600= 25 frames per second (PAL is officially 625 lines with 576 of them visible) (horizontal resolution is not affected - see super-high-res mode) |
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14 March 2019, 13:49 | #6 | |||
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Quote:
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14 March 2019, 13:52 | #7 | |
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Quote:
But I agree - once fast page ram was available this should have been done - your timeframe is probably right. |
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14 March 2019, 13:55 | #8 | ||
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Quote:
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14 March 2019, 13:56 | #9 |
son of 68k
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What could have been implemented without much trouble i do not know, but what's badly missing is clearly chunky and true color modes.
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14 March 2019, 14:08 | #10 | |
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So not so easy (or expensive) back than - but straight forward today (see Vampire) true color: a enhanced HAM mode where you can change all values every pixel would have been easier - again at least with fast page ram ("double CAS") |
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14 March 2019, 14:21 | #11 |
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Here a example how the IIgs provides a colorful GUI with sharp text, using the alternating palette trick on two bitplanes:
edit: pay attention to the Apple-logo in the menu on top of the screen and the same logo on the "system" folder. The menu-bar is in a different screen mode (non-alternating), and instead changes the palette every line. The rest of the screen in using the alternating mode, so the logo further down is dithered. Also take into consideration that these stripes are probably less visible on an analog CRT. Last edited by Gorf; 15 March 2019 at 18:59. |
14 March 2019, 14:39 | #12 | |
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Not in WB.
Quote:
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14 March 2019, 14:52 | #13 | |
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you mean not in High-Res?
Interlace gives you always the same number of bitplanes as the non-interlace mode. On OCS/ECS in High-RES this is of course only 4 (=16 colors). More would only have been possible with faster RAM, as mentioned above, and/or a wider data-bus (AGA). This is not exactly the small improvements or missing modes I had in mind... I was more looking for things that could have been done without changing too much. Some clever ideas the original design could have used. Quote:
Not sure what you mean here... |
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14 March 2019, 15:19 | #14 | |
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I could be wrong and missed a whole stage of the process, but I’m sure chunky would be so much simple than planar. |
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14 March 2019, 15:33 | #15 |
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It depends on how Denise resolves the colors internally - so I am not sure If it could even use the same color-registers...
It seems to do the "look up" stepwise and not in one go - at least, that might explain, why super-high-res and productivity mode do have a limited palette of 64 colors in total: there is only time to get the fist two values of red, green and blue (6-bit) and not all four (12-bit). So this is not only a question of getting the display data fast enough from RAM, but also resolving the according palette-values fast enough. How does AGA do that? simply faster clock? |
14 March 2019, 16:06 | #16 |
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14 March 2019, 16:15 | #17 | |
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14 March 2019, 16:48 | #18 |
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A 256-color chunky mode obviously. Even OCS has the bandwidth for it in lowres.
I understand that extending the palette register file and LUT mechanism from 32 to 256 entries would've increased the cost, but would it really have been prohibitive? And I don't understand the arguments that the whole chip design would have had to be remade from scratch. If you have all the data required read into one or more holding registers, why is it difficult to select a different set of bits for the LUT? I'm sure these chip designs already solve more complex problems than that. |
14 March 2019, 16:56 | #19 |
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:d
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14 March 2019, 16:58 | #20 |
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