Date : Tue, 17 Sep 2002 20:19:39 +0100
From : "james watson" <james@...>
Subject: Firetrack scrolling
With the firetrack routine the bottom 22 character rows are stationary
how do you alter the routine so there is only one character row that is
stationary at the very bottom of the screen i.e for score and energy in
a game, and leave the rest of the whole screen, scrolling. Also what is
the purpose of setting registers 6 and 7
Cheers
James
10 MODE2
> 20 PROCdraw
> 30 PROCassemble
> 40 !addr=&B00:CALL&900
> 50 :
>
>\\ just a crap demo screen so you can see what's going on....
>
> 60 DEF PROCdraw
> 70 VDU28,0,15,19,0,17,132,12,26,17,128
> 80 FOR N%=0 TO 15
> 90 COLOUR N%MOD7+1
> 100 COLOUR 128:PRINTTAB(N%,16+N%);N%;"_";
> 110 COLOUR 132:PRINTTAB(2,N%);N%+16;
> 120 NEXT
> 130 MOVE0,1023:DRAW1279,1023:DRAW1279,512:DRAW0,512:DRAW0,1023
> 140 ENDPROC
> 150 :
>
>\\ wait for vsync
>
> 160 DEF FNvsync
> 170 [OPTN%:LDA&FE4D:AND#2:BEQP%-5:STA&FE4D:]
> 180 =N%
> 190 :
>
>\\ set our timer to timeout in L% microseconds
>
> 200 DEF FNsetwait(L%)
> 210 [OPTN%:LDA#L%AND255:STA&FE44:LDA#L%DIV256:STA&FE45:]
> 220 =N%
> 230 :
>
>\\ wait for our timer to timeout
>
> 240 DEF FNwait
> 250 [OPTN%:LDA&FE4D:AND#&40:BEQP%-5:STA&FE4D:]
> 260 =N%
> 270 :
>
>\\ this macro either enables or disables display by
>\\ changing all palette colours
>
> 280 DEF FNcols(B%)
> 290 FORC%=0TO7:IFB% D%=C%EOR7 ELSE D%=7
> 300 [OPTN%:LDA#C%*16+D%:STA&FE21:]
> 310 NEXT
> 320 =N%
> 330 :
> 340 DEF PROCassemble
> 350 addr=&70:line=&72
> 355 linetime%=64:REM 1 scanline rasterises in 64 microsecs
> 360 FOR N%=0 TO 2 STEP 2:P%=&900:[OPT N%
> 370 SEI
>
>\\ set bits 4/5 of addressable latch for 10k screen
>
> 380 LDA#15:STA&FE42
> 390 LDX#12:STX&FE40:INX:STX&FE40
>
>\\ initialise a few constant CRTC registers
>
> 400 LDA#3:STA&FE00:LDA#&88:STA&FE01
> 410 LDA#10:STA&FE00:LDA#32:STA&FE01
> 420 .loop
>
>\\ wait until vsync, then blank all colours and set timer
>\\ for four character rows time (top of visible screen)
>
> 430 OPT FNvsync \wait for vsync
> 440 OPT FNsetwait(linetime%*32-50) \-50 for fine tuning
> 450 OPT FNcols(0) \all colours off
> 460 OPT FNwait
>
>\\ after four character rows, turn all colours back on
>\\ (we deem this point to be the top of the visible screen),
>\\ set timer to stop us sometime in the bottom half of scrn,
>\\ setup R4/5/6/7 for this top half of the screen, and
>\\ setup R12/13 for the bottom half of screen when recached
>
> 470 OPT FNsetwait(linetime%*138) \reasonably arbitrary
> 480 OPT FNcols(1) \colours back on
> 490 LDA#4:STA&FE00:LDA#15:STA&FE01 \crtc cycle=16 rows
> 500 LDA#5:STA&FE00:LDAline:STA&FE01 \plus these scanlines
> 510 LDA#6:STA&FE00:LDA#255:STA&FE01 \display always
> 520 LDA#7:STA&FE00:LDA#255:STA&FE01 \inhibit vsync this half
> 530 LDA#12:STA&FE00:LDA#6:STA&FE01 \bottom screen start
> 540 LDA#13:STA&FE00:LDA#0:STA&FE01 \ address is &3000
> 550 OPT FNwait
>
>\\ now prepare to jiggle the addr and line variables to
>\\ scroll the screen up by a line (this is effectively
>\\ the bottom of the loop)
>
> 560 LDAline:CLC:ADC#1:CMP#8:BCCskip
> 570 LDAaddr:CLC:ADC#80:STAaddr
> 580 LDAaddr+1:ADC#0:CMP#&10:BCCP%+4
> 590 LDA#&B:STAaddr+1:LDA#0
> 600 .skip STAline
>
>\\ we are currently rasterising the bottom half of screen,
>\\ setup R4/5/6/7 for this bottom half, and R12/13 for
>\\ the top half (next frame).
>\\ NB As the VSync occurs midway through this CRTC update,
>\\ the effects of changing R5 are effectively seen in the
>\\ positioning of the 'top' screen next update.
>
> 610 LDA#4:STA&FE00:LDA#21:STA&FE01
> 620 LDA#5:STA&FE00
> 630 SEC:LDA#8:SBCline:STA&FE01
> 640 LDA#6:STA&FE00:LDA#16:STA&FE01 \16 lines in bottom screen
> 650 LDA#7:STA&FE00:LDA#18:STA&FE01
> 660 LDA#12:STA&FE00:LDAaddr+1:STA&FE01
> 670 LDA#13:STA&FE00:LDAaddr:STA&FE01
>
>\\ that's it! vsync set to occur sometime this crtc
>\\ update, which will be picked up next time round this loop
>
> 680 JMPloop
> 690 ]:NEXT
> 700 ENDPROC