Re: [stella] Illegal opcodes...another question

Subject: Re: [stella] Illegal opcodes...another question
From: "Dennis Debro" <ddebro@xxxxxxxxxxxxx>
Date: Tue, 14 Jan 2003 00:14:09 -0500
Hi Andrew,

> It's a real elegant piece of code, Dennis.

I agree with you there. I've been using skipDraw (without the illegal
opcodes) for Climber for a while now. I'm now trying to understand the
illegal opcode way to see if it can save me some cycles.

> If the carry flag is set then we branch to the
> actual draw code... the y register holds the line number (presumably) 
> on the screen

This is the part I don't understand. When doing skipDraw without the
illegal opcodes I see where the y-register is used to keep track of the
scanline count. In this piece of code though I don't see where y is
updated each scanline. When he skips to the next scanline, the
y-register is not updated.

The code snippet I posted deals with GRP0. On the next scanline Thomas
deals with GRP1 without updating the y-register :confused: Wouldn't the
y-register decrement (or increment) per scanline?

Take care,

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