Six

Can anyone explain how to to do the scrolling chessboard effect, where it appears to continuously scroll towards the viewer?

I figured it was as simple as making a two-color image with the appropriately sized stripes (larger at the bottom than the top) and then moving my copper data, inverting the two colors for each "row" of the chessboard.


However, when I try this, there is a lot of empty space on either side where my bitmap is not displayed, and the effect looks really weak. Thus I'm thinking there must be more to it to make it appear all the way across the screen.

Any suggestions? (Thinking I'm probably missing something simple like changing my bitmap display regs in those lines for overscan...)

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Ray Norrish

Hi,

In it's simplest form, you want a single plane bitmap like this:



You could then either:
Repeat $180 and $182 in the copper for the height of the bitmap,
Then use a simple "filler" to populate the colour values to acheive
movement or slightly faster:
If you know how many different coloured rows you will have in use,
you could pre-create these and move the vertical pointer accordingly.

Rereads your post:
(oh yea, and overscan it of course)

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mr_a500

If you repeat $180 and $182, you could run out of cash pretty quickly. (Who would have thought copper instructions could be so expensive?)

Are you trying to do an effect like Mad Elks' Technological Death? I always loved that "walking cube" on the chessboard background.

AGN

http://www.flashtro.com/page.php?al=alias3464

In this example we have precalculated lines instead of bitmap.
For every line there is copper::move $00e0/2 which chooses line according to sine table.

For flat chessboard You also need BPLCON1 for every line.
Of course all fill data should be in wide enough table to cover every position of lower line.
Upper lines may be shorter in memory.

Is it fast? Efficient? I don't know :)

rsn8887

reminds me of cosmic causeways (trailblazer 2) on c64. How did the guy do that stuff on c64 so smoothly?

Six

THAT is nice. Maybe even easier for me to envision how to pull off than the flat chessboard.

Very similar in technique to the way I'd try to pull that effect off on the 64, interestingly enough.

Could you elaborate on that? Would I be tweaking BPLCON1 to repeat rows from the bitmap?

Because they repeat on a single displayed row, or because I can tweak one of the display regs to "stretch" them?

Thank you all for your advice!

It's a lot of fun trying to adapt what I've done on the 64 all these years to another platform, but without the kind advice of other guys in the scene, it's a real uphill battle

Six

By not actually drawing each line, usually. You can creatively tweak the display regs to repeat lines, and of course a lot of stuff is done in "character sets" so that anything you plot can be repeated as many times as you like onscreen.

Photon

Just take a bitmap like the one Ray suggested and make it 352 pixels wide or more, adjust the copper DIWSTART etc registers for overscan. Then, if there is a maximum of 20 squares visible all the way to the horizon, you make a copperlist with 20x

dc.w $80ff,$fffe
dc.w $0180,$fff
dc.w $0182,$000

The vertical positions of the waits are calculated by a vector routine, if you want it correct. In fact, only one division (or MULS+SWAP, or precalced...) is necessary per point.

If the chess board crosses the NTSC line, insert a dc.w $ffdf,$fffe. In this example you would best do that with an extra 3-command entry like above, so that you won't have to insert anything. Just check when you're crossing line $100 in the copper poke loop - set current entry to $ffdf,fffe+same colors as previous entry and put the correct vertical stop+colors in the next entry.

This is the most correct and cycle-conscious method.

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AGN

http://www.pouet.net/prod.php?which=9096

Frog

ahh... i love chessmate too. I think i try to learn asm to code a chessmate !
Then add a little scroller, a picture, a starfield and a music but i never go further.


There's a nice chessmate : Freddy is Back / PARADOX http://www.pouet.net/prod.php?which=11125

i also remember a great screen on ATARI ST code by Ziggy Stardust (AFAIR). You have to wait some time for precalculation and then he add some vertical waves on the chessmate ! Really cool.

and a PC 256b original chessmate with sourcecode: http://www.pouet.net/prod.php?which=17194

Six

Thanks everyone for all the helpful advice. I'm tweaking the effect to get it just so now, hopefully will have some small intro to show off soon. I think I'm also going to "fade" the colors of the chess squares towards grey as they go back into the horizon.

AGN

another one:
http://www.pouet.net/prod.php?which=14657
http://www-user.tu-chemnitz.de/~sgl/...es/thetop3.zip