BASIC65 proposal: how abouy a raster sync command?

Hi there,

yesterday I took the MEGA65 to our local makerspace and did a bit more BASIC coding there. Of course, I'm mostly interested in coding games. I made use of the COLLISION command, but I noticed that I would also like to sync up my main loop to the monitor refresh rate in a way, so I got the following idea:

How about a command that helps you sync up to the raster frequency, e.g. either something like that:

SYNC 220, 400

this could tell the BASIC65 to register a raster interrupt on raster line 220, which should then GOSUB into BASIC line 400 (similar to how the COLLISION command GOSUBs to a BASIC line)

or something like that:

SYNC 220

to be used in place, e.g. instead of SLEEPing inside your main loop for a certain amount of time, you could tell the BASIC interpreter to wait until raster line 220 has been reached. Basically like reading $D012 and the high bit of $D011 and waiting for a certain number, but in a more convenient, BASIC way. Without arguments, SYNC could just wait until the off-screen interrupt for PLAY, MOVSPR and so on occurs.

maybe there are even other, better versions of how to implement this, so I'll leave that to the BASIC experts, but I think having something like this would make game programming in BASIC so much better!

Zitat von Snoopy

While we're on the subject ... a BASIC command to cook breakfast eggs would also be cool!

??

Yes, something like that, but as a proper BASIC command.

Or as a "SLEEP" command, i.e. just like "SLEEP 3" will halt the program for 3 seconds, "SYNC 220" will halt the program until raster line 220 has been drawn.

Or maybe even both, as many of the BASIC65 commands already have various argument lists. E.g. something that I could imagine:

SYNC - wait until screen has been drawn (i.e. wait until the same interrupt happens which also does MOVSPR, PLAY, and so on)

SYNC rasterline - wait in place until the specified rasterline has been reached

SYNC rasterline, basicline - register an interrupt which occurs at the specified rasterline number and then GOSUBs into basicline number, just like COLLISION does

btw @mods i noticed a little typo in the title of this thread: abouy instead of about - maybe someone could fix this? thanks

oh please don't fix it, i already posted a link to the thread on discord and it would be broken after that fix!

Well it is possible to work around that a bit using PEEK and so on, but remember that the highest bit for the rasterline is in $D011 and you should take that into account as well, otherwise some numbers will trigger on two raster lines (e.g. a value of 30 will trigger on rasterline 30 and also 255+30, i.e. 285).

I'd expect from a proper BASIC command to work flawlessly with any given rasterline number (as long as it's in the given range of course) and that I can rely on that (of course it might trigger a few lines later, but at least it won't get missed at all).

I'm not sure, on the C64 it's 312 lines on PAL and 262 on NTSC, on the MEGA there might be more depending on the resolution

That would be a cool feature, but sadly, it doesn't seem to work on the MEGA65 (testing in the emulator at the moment)

Thanks for your program, but why is the rasterline flashing? It almost seems as if the line is only reached every 2nd frame or so... shouldn't the program run fast enough so that the line is catched every frame?