Page Flip Routine for Basic#
Table of Contents
Page Flip#
10 ;Page flipping routine. After using 20 ;GR.24, GR.9-11, call this routine 30 ;with X=USR(1536) to toggle 40 ;background and foreground page. 50 ;Background page is the one that 60 ;PLOT and DRAWTO effect, and 70 ;foreground is the one that is 75 ;displayed. 80 ; 90 *= $0600 0100 MEMTOP = $02E5 Mem top pointer. 0110 SAVMSC = $58 Video mem pointer 0120 SDLSTL = $0230 Start of DL. 0130 DLPNT1 = $CB Two unused words 0140 DLPNT2 = $CD in zero page. 0150 LDY #0 0160 CLC 0170 LDA SDLSTL Find the 0180 ADC #5 two 0190 STA DLPNT1 display 0200 LDA SDLSTL+1 list 0210 ADC #0 references 0220 STA DLPNT1+1 to video 0230 LDA DLPNT1 memory 0240 ADC #96 and store 0250 STA DLPNT2 them in 0260 LDA DLPNT1+1 unused 0270 ADC #0 part of 0280 STA DLPNT2+1 page 0. 0290 LDA SDLSTL+1 Find area 0300 SEC to store 0310 SBC #31 screen 2 0320 STA MEMTOP+1 safely. 0330 LDA SAVMSC+1 Insure that 0340 CMP (DLPNT1),Y foreground 0350 BNE NORM and 0360 LDA MEMTOP+1 background 0370 STA SAVMSC+1 are 0380 BNE CLEAR different. 0390 NORM TAX Swap both 0400 LDA (DLPNT1),Y of the 0410 STA SAVMSC+1 foreground 0420 TXA pointers 0430 STA (DLPNT1),Y and 0440 CLC the one 0450 ADC #$0F background 0460 STA (DLPNT2),Y pointer. 0470 CLEAR LDA SAVMSC+1 Set up the 0480 STA SCRPNT+1 indexed 0490 LDA SAVMSC addressing 0500 STA SCRPNT command. 0510 LDA #0 Quickly 0520 LDX #30 clear 0530 LOOP STA 0,Y out 0540 INY 7680 byte 0550 BNE LOOP buffer 0560 INC SCRPNT+1 for the 0570 DEX new 0580 BNE LOOP screen. 0590 PLA Unused parameter 0600 RTS Return. 0610 SCRPNT = LOOP+1 0620 ;The SCRPNT pointer is used to 0630 ;modify code on the fly. This 0640 ;allows us to use Indexed 0650 ;addressing which is faster 0660 ;than Post-indexed indirect 0670 ;addressing in the inside loop. 0680 .END
Copy / Clear Page#
10 ;Page flipping routine. After using 20 ;GR.24, GR.9-11, call this routine 30 ;with X=USR(1664) to copy backgrnd 40 ;to foregrnd page. Backgrnd page 50 ;is the one PLOT and DRAWTO 60 ;effect, and foregrnd is the one 70 ;displayed. 80 ;To clear the whole background 90 ;screen, just do an X=USR(1715) 0100 ; 0110 *= $0680 0120 MEMTOP = $02E5 Mem Top pointer. 0130 SAVMSC = $58 video mem pointer 0140 SDLSTL = $0230 Pointer to DL 0150 LDX SDLSTL+1 Find an 0160 INX area 0170 STX FORPNT+1 to store 0180 TXA background 0190 SEC screen 0200 SBC #32 and set 0210 STA MEMTOP+1 up the 0220 STA SAVMSC+1 indexed 0230 STA BAKPNT+1 addressing 0240 LDA SAVMSC commands 0250 STA BAKPNT for 0260 STA FORPNT copying. 0270 LDY #0 Copy 0280 LDX #30 the 0290 LOOP LDA 0,Y 7680 0300 STA 0,Y byte 0310 INY background 0320 BNE LOOP buffer 0330 INC BAKPNT+1 to 0340 INC FORPNT+1 the 0350 DEX foreground 0360 BNE LOOP screen. 0370 PLA Unused parameter 0380 RTS Return. 0390 CLS LDA SDLSTL+1 Make sure 0400 SEC there's a 0410 SBC #31 background 0420 STA MEMTOP+1 screen. 0430 STA CLSPNT+1 Set 0440 LDA SAVMSC indexed 0450 STA CLSPNT addressing. 0460 LDA #0 Fill 0470 LDX #30 the 0480 LDY #0 7680 0490 LOOP2 STA 0,Y byte 0500 INY background 0510 BNE LOOP2 buffer 0520 INC CLSPNT+1 with 0530 DEX zeroes 0540 BNE LOOP2 (clear). 0550 PLA Pull unused argument. 0560 RTS Return. 0570 CLSPNT = LOOP2+1 0580 BAKPNT = LOOP+1 0590 FORPNT = LOOP+4 0600 .END
