Axelay scroll proof of concept

Shiru · Post by **Shiru** » Sat Feb 25, 2012 10:31 am

Just made this small demo (video) that shows Axelay-like scrolling to prove the fact that SNES does not use Mode 7 to do this to some people who had doubts about my explaination how this actually works. No source code is provided because it is really crude (in C), made in no time just to get something working, and because I'm pretty sure everyone here know how to implement this anyway. Maybe the demo could be handy to someone in similar situation, or just as a confirmation that there is no problem to implement this on SMD.

Stef · Post by **Stef** » Sat Feb 25, 2012 11:50 am

The effect is very smooth, and on both planes ! Well done

djcouchycouch · Post by **djcouchycouch** » Sat Feb 25, 2012 2:23 pm

nice!

sega16 · Post by **sega16** » Sat Feb 25, 2012 2:36 pm

Genesis does what Nintendo does
Nice work and I assume it is just an hblank raster

Shiru · Post by **Shiru** » Sat Feb 25, 2012 3:03 pm

Yes, technically it is very simple - vertical scroll position modified every scanline using hblank interrupt and a precalculate table of offsets to create 'perspective' (i.e. just scroll_y+table[scanline]).

sega16 · Post by **sega16** » Sat Feb 25, 2012 5:29 pm

That is what I assumed it was I relay think this could be used for something cool.

HardWareMan · Post by **HardWareMan** » Sat Feb 25, 2012 5:47 pm

Same effect on "Blue Sky" logo in "Vectorman" and sky in "High Seas Havoc" title screen. Nothing special. :3

ob1 · Post by **ob1** » Sun Feb 26, 2012 1:40 pm

Great.
Even though you say the effect is easily achieved, the fact is : you get what the game, graphically, was about. And that is good.

Kudos to you.

ammianus · Post by **ammianus** » Sun Feb 26, 2012 2:39 pm

Interesting effect

Fonzie · Post by **Fonzie** » Mon Mar 26, 2012 7:15 am

Quite cool

One thing however, do you get any CPU time left during VACTIVE? That was always the issue I got with making rasters. And a shooter need a lot of collide computations, life is unfair!

Shiru · Post by **Shiru** » Wed Mar 28, 2012 12:01 pm

I honestly don't know. I'm sure that there still could be enough time for game logic if it is all done properly, i.e. interrupt handler not in C etc. SNES is much slower, but manages to run the game well enough, I don't think SMD will be less capable in this case.

tomaitheous · Post by **tomaitheous** » Thu Apr 05, 2012 7:59 am

Heh. Chris Covell made an Axelay demo too, a few years back. You can see it in the video here:
http://www.youtube.com/watch?v=f-YSnIDsz5U
(starting at 9:50)

Shiru · Post by **Shiru** » Thu Apr 05, 2012 9:28 am

Funny thing that even the announcement in the video states that it is Mode7, although it isn't.

andlabs · Post by **andlabs** » Thu Apr 05, 2012 8:40 pm

I'm guessing more people will recognize it by calling it "mode 7" even though it's not what it actually is. I've been on your side of the fence too :/

Oerg866 · Post by **Oerg866** » Sun Apr 15, 2012 1:41 am

I tried something like this before as the concept behind it is quite interesting.

I am figuring out the math right now to make an universal scaling thing that scales a image to x lines using HBLANK routines