Aw: [stella] Clock Counting...Newbie.

Subject: Aw: [stella] Clock Counting...Newbie.
From: cybergoth@xxxxxxxx
Date: Wed, 17 Oct 2001 16:55:47 +0200 (CEST)
Hi Joel!

> So what is the objective when counting.  Lets say I'm drawing a ball that
> bounces on the screen.   Do I just want to make sure the ball is redrawn at
> the same cycle count each time through my loop??

You normally want to make sure that it takes the same amount 
of cycles wether _it's drawn_ or _not drawn_ on every scannline.

Most of all you want to have the data updated before it get's 
visible on the screen
> Or is there even more too it,  do I have to actually time so the ball is
> drawn before the scan line is drawn on the screen or something like that.

Well, sort of. Your STX/A/Y GRPX must be finished before the raster beam
is going to draw it - every line! So if your object is allowed to move
around the whole screen, you need to have the write finished during 
the HBLANK cycles right after the STA WSYNC of the previous scanline.

> I can see where this could get complex with branches and checking joysticks
> and stuff since everything would take a different amount of clock cycles.

Joystick reading doesn't matter here at all, as it is done *outside* the 
displayed lines, during the overscan or the VBLANK.
(Paddles might be another task though...)

> I'm sorry if this sounds really odd.. I didn't know how to describe it.
> I've read over the stella manual, and the clock counting guide.   I still
> don't quite understand this though.

That's what I felt at the beginning too. Actually I never read the CC guide or
the manual. I never read any manual... :-)

I learned it all by analysing / toying with the sources in the stella 
archive and by scanning it for certain topics like 'Horizontal Positioning'.

I started out with disassembling Starmaster. No kidding :-)
I already completely analysed how the map worked without knowing 
anything about the VCS.

I'm sure most of your questions will get answered quickly, when doing
something practical.


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