understanding fine motion from the book
Hey all,
I'm having more trouble understanding "Making Games for Atari 2600". This time, chapter 9, page 53, the section below, for anyone who knows it:
A now contains (the remainder - 15). ; We’ll convert that into a fine adjustment, which has ; the range -7 to +8. eor #7; this calculates (23-A)% 16 asl asl asl; HMOVE only uses the top 4 bits, asl; so shift left by 4 sta HMP0; set fine position That tricky calculation with EOR and ASL converts the remainder into a value appropriate fo
Okay, DigitalAnthony pointed out that, while using RESP0 alone won't get you right on the left edge, the difference isn't the 5 pixels as I described above, but rather only 3.
Well heck, he's right. At least in Stella and Javatari.
I've attached a slightly-improved version of my test program. I'm putting in an HMOVE, just to be more complete, although it's set up for "zero" and shouldn't change the coarse positioning. I also changed the way the player is drawn, to make it