Lots of AGA graphics capability questions:

[diablothe2nd]

I've already asked two questions elsewhere on the forum, and I have more so I may as well bundle them all into one thread for convenience.

Elsewhere I asked if Alpha Blending was at all possible on AGA chipsets here:

http://eab.abime.net/support-hardwar...-question.html

to save you having to look:

Originally Posted by Thorham

AGA doesn't have alpha transparency so it has to be done in software, and that's going to get slow real quick.

You can set up the palette (preferably in a 256 color screen) so that certain bit plane combinations show an effect like alpha blending and transparency, but you have to calculate the different combinations of fore and background objects. This limits the number of free colors you have, but it can be fast. Doesn't work for hardware sprites, only for blitter and CPU sprites.

Actually, Diablo 2 uses the palette technique for transparancy in 256 color screens, so it's certainly possible.

Real alpha blending and transparency are, however, still a pain because you 1) have to do the blending/transparency calculations, and 2) you have to do it in HAM, or there's little point.

I also asked elsewhere:

Originally Posted by diablothe2nd

what's the maximum resolution image an unexpanded A1200 can EIGHT WAY scroll and still have enough ram left for a few bobs/sprites and gameplay? i'm thinking top down racers, shooters etc (think Overdrive, Micro Machines, Chaos Engine, Total Carnage etc)

(shall paste the answer here when it's answered)

Now for my third, fourth and fifth question

I've seen demos that pan and zoom images larger than the screen space. I've also seen in Pinball Illusions how the screen can switch between zoomed in and zoomed out (hi res laced?) modes. What I wish to know is, has this zoom AND pan effect been done in a game? specifically top down racing games.

If so, does this mean that BOB scaling is possible? if so, how can this be done in blitz (or asm)?

i'm currently fleshing out ideas for a top down Formula 1 game as my first major project in Blitz Basic and I was thinking wouldn't it be cool if the "camera" zoomed out as the car got faster so you can see more infront. of course this would require also scaling the other cars (bobs) with it.



EDIT - Here's a pic of what I had in mind when at slower speeds:



pre-rendered car is modelled in 3d and rendered to sprite sheet.



tracks would be pre-rendered too. view is almost overhead-isometric

[hooverphonique]

Sorry, but I think you'll be hard pressed to write any amiga game at all if you can't answer most of those questions already..

there's no hardware support for real alpha blending, but you can have a limited number of semi-transparent colors by cleverly arranging bittplanes and palette - read up on how bitplanes work to understand how to do this..

there's no hardware scaling support either, but some demos creates the "illusion" by modifying the bitplane scroll value across the scanlines, which will give "hardware scaling" between 0 and 16 pixels, but that consequently requires you to have the source bitmap (the race track) in memory in "no. of zoom levels"/16 sizes. This is probably not feasible..

[diablothe2nd]

Originally Posted by hooverphonique

Sorry, but I think you'll be hard pressed to write any amiga game at all if you can't answer most of those questions already..

Thanks for the vote of confidence , no REALLY, thank you. /sarcasm


i have read about bitplanes and such. I'm asking these questions as i've not found anything specific to my question.. that, and perhaps some good people here would be able to tell me things that i simply wont find with any amount of digging

saying i wont be able to write ANY amiga game just because i'm asking these kind of questions isn't productive and isn't welcome. besides, i've already written some basic test games in BB already so ner

thank you though for clarification on zooming/scaling support and adding to the alpha answer

[diablothe2nd]

Originally Posted by hooverphonique

some demos creates the "illusion" by modifying the bitplane scroll value across the scanlines, which will give "hardware scaling" between 0 and 16 pixels, but that consequently requires you to have the source bitmap (the race track) in memory in "no. of zoom levels"/16 sizes. This is probably not feasible..

just trying to understand this bit some more as scaling the pre rendered images is no problem to me, i just need to change to output resolution and save it in a different size.

When you say not feasible, Are you referring to ram constraints for having to store so much image data? or data speed (or lack thereof) to be able to switch between them on the fly? could this be done and be provided as an option if fastmem and/or an accelerator is detected? and obviously disabled if not?

[emufan]

i found a 4 bitplane image zoomer asm source code on lsd-cd1. maybe it will help you a littlebit

i also uploaded the whole assembly folder from that cd, with more source codes.
FILES.BBS inside the archives, lists the content of those files. zoned.

[diablothe2nd]

thank you thank you thank you thank you

[emufan]

Originally Posted by diablothe2nd

thank you thank you thank you thank you

heh, np. just trying to help

Edit: maybe i found one more zoom example. asm again. on AmigaCodersClub ACC 28: i upload the disk to the zone, and attach the file here.

ACC-028.ADF -> Archives/P_Kent.LZH -> scaler.s

[hooverphonique]

Originally Posted by diablothe2nd

When you say not feasible, Are you referring to ram constraints for having to store so much image data? or data speed (or lack thereof) to be able to switch between them on the fly? could this be done and be provided as an option if fastmem and/or an accelerator is detected? and obviously disabled if not?

I wasn't trying to demotivate you, I was just saying that the bitplane/alpha stuff is so basic that you might want to get a firm grasp of how that works before going any further

By "feasible" I meant in terms of ram - from one of your earlier posts, I got the impression that you wanted the track to be as large as possible

[diablothe2nd]

It was pretty de-motivational lol

i know enough about bitplanes to be able to set them up in blitz basic, and for every extra bitplane you use it effectively doubles the colours and the ram needed to store the data. i also knew enough that bobs have a transparent colour. What i didn't know is how to create the illusion of alpha blending as i'm certain i've seen it in games before.

i would like the track to be representative of real world tracks, yes. whether that means scaling things down and slowing the cars down to get a similar lap time to real world or not so be it.