4th tutorial on ASM- and HW-coding

[Vikke]

Hi again,

This time I make the same effect as last time, but on a larger copperbar. This needs a larger Hshift-value than 16px, so a little trick is used, but not modulos this time. In the LHA there are 2 executables, one is compiled from the given source, the other using a slightly different method. Compare the 2 methods, and you should notice that the one supplied in the source looks better.

Next time it will be a new "effect", using the Blitter and some fonts... what can it possibly be?

Site: http://vikke.net

[hooverphonique]

in the description on your site, you mention "bitfield" multiple times.. I think the term generally used is "bitplane" :-)

also: sine scroller?

[Vikke]

Yes, I will change the wording to bitplane instead of bitfield. Not that bitfield is totally wrong, but bitplane is more commonly used in Amiga programming. I shouldn't be writing the tutorials in the middle of the night. But I just had to watch the Revision 2013 stream last night

Well, before you can make a sine-scroller you need to make a normal one first. But a sine-scroller will come soon.

[CFou!]

Originally Posted by Vikke

Well, before you can make a sine-scroller you need to make a normal one first. But a sine-scroller will come soon.

but horizontal scolling code is completely different from sinus scroll

[StingRay]

Originally Posted by CFOU!

but horizontal scolling code is completely different from sinus scroll

Nope, not really. You still need a normal horizontal scroller for doing the sine scroll, a sine scroller is not much different to a normal scroller.

[CFou!]

Originally Posted by StingRay

Nope, not really. You still need a normal horizontal scroller for doing the sine scroll, a sine scroller is not much different to a normal scroller.

so we have not same method to code it !

[Vikke]

I can think of 2 totally different methods for doing a sine scoller with the blitter. One implements a standard horizontal scroller to some degree, the other method is .... something I have never even tested, but it hit me as a possibility a couple of weeks ago.

Perhaps I will have to test out this "new" method at some point, it could be a really really good way of doing it, or really shitty

[StingRay]

Originally Posted by CFOU!

so we have not same method to code it !

While that might be true anyone who understands how to code a standard horizontal scroller is able to code a sine scroller too! Since the principle is the same: scroll some characters from right to left (or vice versa), the only difference is how you blit/draw the characters. A sine scroller is an "extended version" of a standard scroller just like a gouraud triangle filler is an "extended version" of a standard flat triangle filler.

[hooverphonique]

yes.. the revision stream was not to be missed saturday and sunday night :-)

in the past I've done my sine scrollers based on a regular horizontal scroll as well.. since then, I've thought that it must be possible to do one where you blit the vertical slice directly from the font data and onto the screen - never tried implementing it, though...

[musashi9]

Great tutorials, I love them.
I can't wait for the next one.

[leonard]

Hi,

thanks for these tutorials. I try to setup a small test on amiga 500, OCS. I'm looking for a good video registers init for 320*256 pixels, on OCS. ( I already have some code doing this, but for AGA)

In your sample I get that init, but it's for 320*200, how should I modify values to get 320*256 ?

move.w #$3200,$dff100 ; 3 bitplane lowres
move.w #$0000,$dff102 ; horizontal scroll 0
move.w #$2c81,$dff08e ; DIWSTRT - topleft corner (2c81)
move.w #$f4d1,$dff090 ; DIVSTOP - bottomright corner (f4d1)
move.w #$0030,$dff092 ; DDFSTRT - max overscan $0018
move.w #$00d0,$dff094 ; DDFSTOP - max overscan $00d8

thanks

[Vikke]

For 256 scanlines,you have to change DIWSTOP to $2CC1.