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

Subject: Re: [stella] Clock Counting...Newbie.
From: "Glenn Saunders" <cybpunks@xxxxxxxxxxx>
Date: Wed, 17 Oct 2001 10:54:44 -0700

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.
Is that the issue?

The hardest part of the program is the scanline kernel, the visible part of the display. This is the part that has a lot of decisionmaking to do on a scanline by scanline basis. The code has to determine on which scanline to start displaying the sprites, and which scanline to stop displaying them. It has to index through the sprite graphics and any playfield graphics. It has to (potentially) update the playfield in mid-screen.

Since there are only 76 cycles per scanline, 74 if you use WSYNC, and even fewer when you execute an HMOVE to reuse sprites, there really isn't enough time to make full use of all the capabilities of the 2600 all the time, at least not without some serious tricks and/or extra hardware.

Once you settle on how to do this stuff, the rest is considerably easier because there is a fairly generous amount of time available during VBLANK to read input, process collisions, and update the X Ys of the objects. It's enough time for most 2600 games, at least.

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