21 April 2024, 10:26 | #81 | ||
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By comparing it to the theoretical bandwidth of the chip ram bus and by measuring against a dummy algorithm that writes long words to chip ram. |
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21 April 2024, 10:33 | #82 | ||
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Looks like we are back again to the "specification vs. code" discussion. The specification does not grant you alignment guarantees, nor that you can access "out of bounds" of the source. Thus, the code cannot perform them. |
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21 April 2024, 10:53 | #83 | ||
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21 April 2024, 10:58 | #84 | |
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It's a library function for copying images. So that is what it does. It's up to the programmer who is using it to decide whether losing a bunch of colour depth information is what they wanted or not, the OS function is just there to do what is asked of it. |
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21 April 2024, 11:19 | #85 |
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The specs are not incomplete. Implementing something that expects more than what the specs demand is just an interface violation - quite simple. Just because it makes some algorithms "inconvenient" does not justify to make the life of the caller "more inconvenient" because the function could have some unforeseen "sideffects" if it makes out of bounds accesses.
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21 April 2024, 11:47 | #86 | ||
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21 April 2024, 12:53 | #87 | |
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But memory limits existed, and there is no alignment constraint for planar bitmaps either. For AGA, there are some constraints, but that's why AllocBitMap() has the BMF_DISPLAYABLE flag, namely to ensure that the bitmap is suitably aligned to be loaded into the hardware. However, there is no documented requirement in the blitter functions (unlike the viewport functions) that such a constraint needs to be satisfied. |
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21 April 2024, 13:18 | #88 | ||
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21 April 2024, 15:09 | #89 |
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Yeah, but that's the classic problem with OS design. An API was specified with certain current hardware limitations in mind (such as a palettized display). Later true colour hardware comes along and just works in a fundamentally different way.
But applications have been written to the old API with it's old assumptions, so support for new hardware has to do the best it can. The specifications might not say it needs to handle the situation in a specific way, but implicitly it does for existing software to still function as you'd expect. |
21 April 2024, 19:06 | #90 | |
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So what do you suggest? Let old applications crash or render nothing on high-color screens? Or let applications crash because they don't satisfy new alignment constraints we're making up 30 years later because it simplifies one algorithm? We don't have the luxury in Amiga Land to request new revisions from software authors, or hardware vendors, just because it is "more convenient" in some place of the Os or the graphics stack.
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21 April 2024, 19:35 | #91 | ||
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Many hardware registers just don't care about being read, either. |
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22 April 2024, 06:39 | #92 | ||
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I'm curious know how much difference it made. What machine did you test it on, and what results did you get for your blitbitmap code vs writing longwords? |
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