How does the laser weapon in Gradius and Parodius work? By which I mean the laser stays coherent no matter how you are moving, as opposed to being compressed or discontinuous if you just, say, used the player's current abscissa every few frames to elongate the beam (which is the simplest method I could think of).

Your English is very good... 2 good 2 b true cause I have red your post 3 times now... still don't get it...

Let's reduce things to a more standard level of English : the laser (and its length at that moment) is moved identically to the movement of the ship. His question is: how did they do that?

it's simply a matter of recalculating the Y position of the beam (same as your "ship" and reprint the darn thing.
since Gradius is screen 1, this is done withing a milisecond. Screen 1 is charbases which means FAST.
there ya go. no biggy.

You sure it isn't screen 2 ?

It *is* screen 2, in patternmode

might also be screen 2. But it's the same difference.
screen 1 has great pattern mode, same as screen 2 but maybe faster!? dunno.

scr1 = 2 colors per 8 chars
scr2 = each char has unique colors (max 2 on a row ofcoz)

huh? no way dude. screen 1 has same specs. 2 colors per 1 row of char, like scr2.

read again ^_^

scr1 = 2 colors per 8 chars <-- and max 2 colors on a row, naturally..

scr2 = each char has unique colors (max 2 on a row ofcoz)

so u say. char 0-7 all have the same color on row 0 for example? (thaz crap, I've dun it 10000 o'times back in the days)
(only in STANDARD screen mode, duh)
or am I totally stupid?

what I'm saying is that char0..7 have 2 colors, char 8..15 have 2 colors, char 16..23 have 2 colors etc. etc.

So, the @ABCDEFG chars (64..71) have 2 shared colors .. meaning your 'A' can be fore:15 back:4 (for white on blue) but the other chars in that 'group' are like that then as well.

Which is why games are generally taking place on screen 2 ... just have a peek at Konami games orso .. and see what the emulator says about the screenmode.

Lemme dig into some old basic stuff I've got laying around .. I did that stuff (15 years ago, gheh) in screen 1, each char it's own color set.

iirc there's no screen 1 or 2 in asm, rite? Just patternmode, and you need to set a bit for scr2-mode orso. I remember Edwin doubting the very same issue, some half year ago, because he had the asm-method in mind.

read again ^_^

I said BASIC, but I used VDP reg's to set that pattern mode indeed, hmm a mix of sc1 and sc2. gheh.
In asm there's also sc1, 2 and more. but like BASIC it's merely a matter of some VDP presets for each screen.

ro, the confusion about the screen capabilities probably comes from some old basic apps. Screen 2 in basic hides the fact that it's a pattern mode and emulates a normal graphics mode by setting a different pattern at each location. Most basic apps I saw that used the Sc2 pattern mode did so by setting screen 1 and then setting some VDP registers to enter the sc2 pattern mode. The advantage is that basic can still use it as a pattern mode like it would in screen 1, but you have the screen2 pattern where you can use 2 colors per line.