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Forum Index : Microcontroller and PC projects : inverting the maximite screen
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BobDevries Senior Member  Joined: 08/06/2011 Location: AustraliaPosts: 266 |
I just wrote a few lines of BASIC to invert the screen using Geoff's new pixel() command. It takes over two minutes to do it this way: 10 PRINT TIME$ 20 FOR x=0 TO 480 30 FOR y=0 TO 432 40 z=PIXEL(x,y) 50 IF z=0 THEN z=1 ELSE z=0 60 PIXEL(x,y)=z 70 NEXT y,x 80 PRINT TIME$ Rearranging the order of the FOR-NEXT loops actually makes it slower! Regards, Bob Devries Dalby, QLD, Australia |
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| RossW Guru  Joined: 25/02/2006 Location: AustraliaPosts: 495 |
I don't (yet) have one of these beasties, and it's a LONG time since I was forced to endure BASIC, but surely the if-then-else test is hideously inefficient. Doesn't the basic include an XOR? replace lines 40, 50 and 60 with pixel(x,y)=pixel(x,y) XOR 1 |
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| BobDevries Senior Member Joined: 08/06/2011 Location: AustraliaPosts: 266 |
As far as I can see in the manual, the only XOR is a logical operator. I'll try that to see if it's suitable. Regards, Bob Devries Dalby, QLD, Australia |
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| BobDevries Senior Member Joined: 08/06/2011 Location: AustraliaPosts: 266 |
Indeed, the XOR example works (thanks, RossW) and reduces the execution time to just over 1 minute; better, but still painfully slow. Regards, Bob Devries Dalby, QLD, Australia |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Another way is pixel(x,y)=not(pixel(x,y)) testing and writing to each pixel is a lot of work ( 207360 pixels all up ), and I doubt the Maximite MMBasic is optimised for fast video processing, plus its a interpreted language, so thats a lot of processing. A fill line (0,0)-(480,432),1,"BF" takes 141 milliseconds, cause its a single command that is run once, but thats not what you want. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| BobDevries Senior Member Joined: 08/06/2011 Location: AustraliaPosts: 266 |
Yes, the NOT function works too (thanks, Gizmo), and its time is 1 minute 10 secs. Regards, Bob Devries Dalby, QLD, Australia |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
Does that mean the XOR is faster ("slightly over 1 minute") than NOT ("1 minute 10 sec")? Can you read the video memory a byte-at-a-time, XOR with 255 (0xFF), write it back, and step a byte? That'd reduce the for-next loop 8-fold which should be almost an order of magnitude faster. (We're still talking about many seconds though). |
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| BobDevries Senior Member Joined: 08/06/2011 Location: AustraliaPosts: 266 |
The NOT version is slightly faster. No only one pixel is accessible at a time using the pixel() function. There's no other way to access the screen RAM (or any other RAM). Regards, Bob Devries Dalby, QLD, Australia |
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stuarts Senior Member Joined: 15/06/2011 Location: AustraliaPosts: 199 |
Sounds like its time for Peek() and Poke() Time is nature's way of keeping everything from happening all at once. |
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| BobDevries Senior Member Joined: 08/06/2011 Location: AustraliaPosts: 266 |
I'd be happy to see the following additions: DRAW GET PUT LOADBMP Regards, Bob Devries Dalby, QLD, Australia |
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