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Forums > C64 Coding > LDA (ZP,x)
2016-05-16 14:31
oziphantom

Registered: Oct 2014
Posts: 502
LDA (ZP,x)

Has anybody ever used this opcode and if so what for?
 
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2016-05-20 16:30
oziphantom

Registered: Oct 2014
Posts: 502
Ah that doc in a round about way defines what H is. I've seen it on other sites but nothing defined H. Although it seems to be a typo and it should be H+1. Thanks
2016-05-20 22:13
HCL

Registered: Feb 2003
Posts: 731
Quoting lft
Another thing I've had in mind, but never actually implemented, is this: Suppose you're doing something like kefrens bars with open sideborders. You repeat the last line of a row of characters and modify the font on the fly. But in the borders, you repeat sprite data, let's say one sprite on either side. That means you have a single graphics buffer consisting of 46 bytes, but those bytes are distributed somewhat irregularly in RAM. So make a table in zp consisting of 46 pointers to them. Then use (zp,x) in the drawing operations. You can even access neighbouring cells with (zp-2,x) and (zp+2,x).

Yepp, Slammer is right.. That's what i did in Royal Arte :), but without border :P. Totally forgot about that, and i never thought i ever used (zp,x) :).
2016-05-21 08:56
Wisdom

Registered: Dec 2001
Posts: 91
Used it in Thread Over and in Matrix 16. Might be useful in some size-coding cases.
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