COMMENTS: A cute little credits type verticle scroll (or pan, if you like..) Written by Draeden /VLA - 7-25-93 INCLUDED MAY BE ONE OR MORE OF THE FOLLOWING: VSCR2.EXE VSCR2.ASM <- Scrolly with small text VSCR3.EXE VSCR3.ASM <- Scrolly w/ 4x as big text VSCR4.EXE VSCR4.ASM <- Scrolly w/o shading MODEX.INC <- My modeX routines/ macros MXFONT2.INC <- Cheap and simple modeX text routines And possibly some more stuff... depending on where you got it.. Alright.. been a while since our last tutorial code/text, but I think this simple ditty is worth the wait. I decided to write a verticle scrolly 2 days ago at 10pm and got it looking good around 11:30... Today I decided that I should release the code, since what I did was SO DARN SIMPLE. OK, maybe the program is a little hairy at parts because of the messing with the palette, but the continuous scrolling IS pretty simple... Anyways, to the code... Well, first off, let me explain what I'm doing... I am panning downward (increasing the STARTING OFFSET register) by the width of the screen for each frame. When I reach the offset that would make it so I am only showing the second page, I go back to the minimum offset. Lemme show off my ansi skills and draw a diagram. =) SCRW = width of screen in bytes- for a 320 wide screen that would be 80 bytes offset ~~~~~~ 0 旼컴컴컴컴컴 � This is the split screen area � � � base 쳐컴컴컴컴컴 <- The minimum of our start offset � This is the top of page 1 � � � � � � base + 쳐컴컴컴컴컴 <- The maximum we let our START OFFSET get to height of � scroll*SCRW� And this is page 2 � � � � � 쳐컴컴컴컴컴 � <- A varying amount of extra video memory / <- where you can put whaever you want / <- Possibly a font, so you can copy it quickly � <- with write mode 1 쳐컴컴컴컴컴 <- This is the 'next line' buffer area � <- We want to write whatever we want displayed next 64k 읕컴컴컴컴컴 <- Right here CurOff = the current StartOffset What you do each time you pan the screen up on pixel is: 1) Increase CurOff by SCRW and set START OFFSET register 2a) Wait for a verticle retrace 2b) Update the palette (this is only what I did.. obviously it is not necessary if you don't want that palette trick.) 3) Copy a line from the 'next line' area to CurOff - SCRW (or the old CurOff) 4) Copy the same line from the 'next line' area to CurOff + ScrollHeight*SCRW - SCRW 5) Increase the pointer used to access the current line in the 'next line' area, if it goes beyond the max, reset to the min and clear out the 'next line' area and fill with next text... This will cause a slight messup at the bottom of the scroll because you are displaying stuff that hasn't been updated yet... You COULD fix that by carefully timing the writes to the video card, but I say just cover it up with the split screen... Kinda lazy, aren't I? In this example I didn't have to mess with it cause the messed up area was of the color black... and black on black isn't really noticable.. Ok, to make a stupid story short... ;) I did the palette trick by setting up the screen similiar to the old palette induced 'copper bars'... Maybe that's not what to call them, but anyways, every line has a different palette color. First line is a 1, then 2, 3, 4, and so on... Then I just change the palette in a way similiar to the ol' palette bars, with the bars following the edge of the scroll area... Hmm.. maybe if you were really interested, you could go into the program and change the MAXCOLORS to 200 or so and then set the split screen to 0, so you can see what is really happening to the screen data and the palette... Enuff docs.. I'm getting bored... =) Oh, yeah, you can use this code for whatever you want. Just give VLA some credit for our hard(?) work... And we take no responsibility for whatever this code does, known or unknown. If you don't like our color selection, tough. =) BTW, I don't care if you rip our code as long as you greet us. Blah blah blah blah blah. (That says it all.) END COMMENTS