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Old 20 December 2019, 15:57   #1
deimos
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Blitter clearing a line without src channels?

I'm clearing my scratch buffer after drawing a line into it. I don't need to just clear only the bits that have been previously been set, I'm happy to just write entire words full of zeros.

Will I save a tiny amount of time if I just set the minterms to zero and don't enable the C source channel?

And if I do, can I also disable the A channel, or will that break the blitter's line drawing algorithm? Will that save me more time?
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Old 20 December 2019, 18:37   #2
DanScott
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This is a really interesting question, and one that I don't have the answer to, but will be very interested to know thinking outside the box is always great!
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Old 20 December 2019, 18:54   #3
deimos
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Quote:
Originally Posted by DanScott View Post
This is a really interesting question, and one that I don't have the answer to, but will be very interested to know thinking outside the box is always great!
My experiments so far seem to indicate that it doesn't work, any deviation from the norm results in garbage, but that might just be me.

I can understand requiring A, but I don't see why C would be required.
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Old 20 December 2019, 19:00   #4
Toni Wilen
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http://eab.abime.net/showpost.php?p=206412&postcount=6
http://eab.abime.net/showthread.php?t=63959
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Old 20 December 2019, 19:14   #5
deimos
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Right.

Ok.
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Old 10 January 2020, 15:56   #6
Photon
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I doubt there's a gain or I would have had it in my codebase instead of XOR mode (or possibly 0 mask), because I remember I tried the blocky word linedraw clear back in the day. It seems your only chance is to disable B and measure, and it would be a quick test.
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Old 12 January 2020, 03:42   #7
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Might setting SING help here? Something I've wondered about is whether or not with SING writes are reduced. If so, then there might be a small amount of time saved blanking lines with slope <1 and >-1 and with minterm set to 0.
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