Xenon 2 Image Scaler - 68020 Improvement Challenge

[lmimmfn]

Originally Posted by Galahad/FLT

So, it seems 30 years later, the most impressive coding in Xenon 2 wasn't the game itself, it was the realtime zooming for the logos in the intro!

Haha, my thoughts exactly, i always assumed it was prerendered.
The game itself, another story, never understood the praise and ran slow as crap.

[jotd]

the graphics are good, the music is good, the power ups are good. but it's just too hard specially in the later levels and you can't make progress/get level codes like in other Bitmap Bros games.

and levelskip is useless because you need to get power related to the level you're going to play (like in chaos engine where the levelcodes save the money you have)

[ross]

Damn, during the night I thought about the code, then today I wrote a few lines, but the laziness remains, so I don't know when I'll continue

Ok, here is a fixed-point math helper code to generate the 'zoom table' (actually it is a shrink columns bit-mask):

m_step  EQU 32

    lea mask(pc),a0
    move.w  #(65536/m_step),d3
    moveq   #0,d1

.r  moveq   #0,d0
    move.w  #(65536/2),d2       ; .5
    moveq   #32-1,d7            ; 32 bit mask
.m  add.w   d1,d2
    addx.l  d0,d0
    dbra    d7,.m
    move.l  d0,(a0)+
    add.w   d3,d1
    bcc.b   .r
    ext.l   d7
    move.l  d7,(a0)+            ; full image
    rts
   
mask

I created this generic code for 2 reasons:
- I needed a mask that wasn't limited to 16 bits
- I had to be able to use more than 16 zoom levels

This is because on the A500 the zoom speed is very limited (I don't think it even reaches 12fps when the image visible part is big..), while on the A1200 you can reach 50fps.
So you would have a magnify with a 'right' speed and a less coarse transition between the different images.

With m_step=32 you double the generated images, but maybe for a better speed 48 is right.

Off course using a value of 16 for m_step and extracting only 16 bits from the mask would give you exactly the ZOOMTAB used in Xenon2.


EDIT: however, the ultimate goal remains to not even use the mask (or rather, use it indirectly)