Apple-2-SW
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greenscale
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Charles Mangin 2019-01-05 13:51:21 -05:00 committed by GitHub
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1 changed files with 20 additions and 12 deletions
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GREENSCALE.s
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@ -2,6 +2,13 @@
**************************************************
* Low res monochrome image display
*
* to do:
* detect virtualII vs openemu or real hardware
* (or other emulator)
*
* further optimization, to speed up framerate
*
**************************************************
* Variables
**************************************************
@ -16,9 +23,6 @@ CHAR EQU $FD ; byte at PLOTROW,PLOTCOLUMN
PLOTROW EQU $FE ; row in text page = ROW/2, remainder = nibble
PLOTCOLUMN EQU $FF ; col in text page == COLUMN
RNDSEED EQU $EA ; +eb +ec
IMGHI EQU $CE ; image data addres, HI
IMGLO EQU $CD ; image data addres, LO
@ -102,17 +106,16 @@ END STA STROBE
**************************************************
* MAIN LOOP
* waits for keyboard input
**************************************************
MAIN
LDA #$40
LDA #$40 ; image data starts at $4000
STA IMGHI
LDA #$00
STA IMGLO
STA FRAMENUM
STA FRAMENUM ; frame #0
NEXTFRAME LDA #$00
NEXTFRAME LDA #$00
STA PLOTROW
TAY ; Y IS PLOTCOLUMN
MAINLOOP
@ -127,14 +130,14 @@ PLOTCHAR
LDA LoLineTableL,X
STA $0
LDA LoLineTableH,X
STA $1 ; now word/pointer at $0+$1 points to line
STA $1 ; now word/pointer at $0+$1 points to screen line
LOADQUICK
LDA CHAR
STA ($0),Y
STA ($0),Y ; store byte at LINE + COLUMN
INC IMGLO ; increment IMGLO
BNE INCCOLUMN ; if IMGLO == 0
INC IMGHI ; increment IMGHI
BNE INCCOLUMN ; not rolled over, skip
INC IMGHI ; if IMGLO == 0 increment IMGHI
INCCOLUMN ; next column of 2 pixels
INY ; Y IS PLOTCOLUMN
@ -148,7 +151,7 @@ INCROW INC PLOTROW
LOOPTY INC FRAMENUM
LDA FRAMENUM
CMP #$08
CMP #$08 ; *** how many frames? ***
BEQ MAIN
JMP NEXTFRAME ; wait for input...
@ -157,6 +160,11 @@ LOOPTY INC FRAMENUM
**************************************************
* Data Tables
*
* I was looking up each nibble, then converting
* the two nibbles to a full byte, but it's
* considerably faster to lookup a full byte at
* a time, skipping manipulating nibbles.
*
**************************************************
COLORTABLEV2 HEX 00,02,06,01,04,05,08,03,0C,09,07,0A,0B,0E,0D,0F ; Low res colors from darkest to lightest for Virtual ][