Can I have some preset HDMA tables?

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Main - ROM Hacking - Can I have some preset HDMA tables?

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cory21391

Posted on 08-08-07 06:00 PM

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yeah, I got HDMA now, but.... Well, I suck at animations and suck even more at wavey animations. So, are there any preset (3 or 4) hdma tables to simulate H-Scroll waviness? (kinda like DCK water levels) I tried to use 3 tables and after every so many wai's I'd change the table (the order was 1, 2, 3, 2, 1 ....etc.) but it was quite horrible

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blackhole89

Posted on 08-08-07 06:10 PM

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If you want the background to be animated, preset tables won't work by definition. What you, however, can do the following:
- Make a simple sine table for one period in ROM, going from like -5 to +5 in terms of amplitude and stretched out on whatever you want the wave length to be. Powers of 2 would make the math to do in the following easier.
- Create a counter that is incremented every frame and wraps around to zero after it hits the number of entries in the sine table.
- Have a subroutine generate an HDMA table in RAM that does as follows:
- 2 bytes write twice to register 210F (BG2 hscroll)
- fill it with entries like:
[$02 or whatever you want the number of scanlines for a "step" of the wave]
[2 bytes: base BG2 scroll + the entry of the sine table at [(entry#+counter) mod sine table length]
- make it be used as described

While I don't have the tools at hand to test it out and no time to write it out as code, it should work roughly as that.

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cory21391

Posted on 08-08-07 06:20 PM

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Couldn't i just use preset hdma tables as "frames" and wai so many times and change the table on the channel and loop it? I actually did this, but my values for BG2 scroll sucked and it just like moved back and forth...

an example would be:


hdmaloop:
  jsr hdma1
  jsr hdma2
  jsr hdma3
  jsr hdma2
  jmp hdmaloop

hdma1:
  stz $420C
  lda #%00000010
  sta $4300 ;HDMA transfer settings
  lda #$0F
  sta $4301 ;sets destination to $0F, BG2 H-Scroll
  ldx #hdmatable0
  stx $4302 ;sets source offset
  lda #:hdmatable0
  sta $4304 ;sets source bank

  lda #$01
  sta $420C ;enables HDMA transfer through channel 0
  jsr wailoop ;wai's so many frames
  rts

hdma2:
  stz $420C
  lda #%00000010
  sta $4300 ;HDMA transfer settings
  lda #$0F
  sta $4301 ;sets destination to $0F, BG2 H-Scroll
  ldx #hdmatable1
  stx $4302 ;sets source offset
  lda #:hdmatable1
  sta $4304 ;sets source bank
  lda #$01
  sta $420C ;enables HDMA transfer through channel 0
  jsr wailoop ;wai's so many frames
  rts

hdma 3:
  stz $420C
  lda #%00000010
  sta $4300 ;HDMA transfer settings
  lda #$0F
  sta $4301 ;sets destination to $0F, BG2 H-Scroll
  ldx #hdmatable2
  stx $4302 ;sets source offset
  lda #:hdmatable2
  sta $4304 ;sets source bank
  lda #$01
  sta $420C ;enables HDMA transfer through channel 0
  jsr wailoop ;wai's so many frames
  rts

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blackhole89

Posted on 08-08-07 08:55 PM

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You could do that, only it would use up an unnecessarily high amount of memory unless you went for a really low-resolution effect and wouldn't work if the background had some scroll of its own...

Also, unless the wavy BG is the only thing your ROM is going to do, what you wrote there could be considered very bad style at best... you should implement that kind of code into some kind of main loop/NMI routine instead.

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cory21391

Posted on 08-08-07 09:05 PM

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yeah, I could optimize this and put the table's address in RAM, and just change the source address in vblank or something... But, uh, I don't really understand all of your suggestive code. I may sound stupid for asking this, but "what's a sine table?" the only place I've heard sine is somewhere in Alg 2 but I wasn't paying attention

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MathOnNapkins

Posted on 08-08-07 09:47 PM

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Sine just means it looks like a nice smooth wave (rather than a jagged wave). You want animation to look smooth, not stilted.

And I guess you figured out that HDMA effects aren't automatically awesome unless you put some work into them.

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blackhole89

Posted on 08-08-07 10:10 PM (rev. 2 of 08-08-07 10:25 PM)

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The blue one is a sine wave. Wikilink is go
Trigonometric functions are something you always should know, especially when messing with computer graphics

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cory21391

Posted on 08-09-07 05:29 PM

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And I guess you figured out that HDMA effects aren't automatically awesome unless you put some work into them.

lol yeah, at first I was actually stupid enough to think that if I copied the BG2 wavey scroll table from qwertie's GFX doc it would simulate waves.... AHAHAHA!!! yeah.... I feel dumb now

But anyways, I think I know how to sort this out now. It'll take some work, but then again, so will programmnig an entire game...

thanks again for the help

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Ailure

Posted on 08-11-07 03:43 PM

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Posted by blackhole89
Trigonometric functions are something you always should know, especially when messing with computer graphics

Indeed. I realized this for a month ago when I was making a quick clock in openGL. I had to read a bit in Wikipedia to get it going, since it's been ages since I learned Trigonometry.

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smkdan

Posted on 08-12-07 02:28 PM

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In WLA, .DBSIN and .DWSIN let you create tables very easily. You enter the starting angle, number of entries, rate of oscilliation, amplitude, and an optional additive. It'll conveniently create a bunch of signed numbers from it.

cory21391

Posted on 08-13-07 05:42 PM

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well, as far as Trigonometric functions go, I'm about to be in 11th grade, so this year I'll be taking pre-calc. so yeah...

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Main - ROM Hacking - Can I have some preset HDMA tables?

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