Fast plotting routine for MODE 0
Converted from the Mode 1 routine by The Executioner
Input: DE = X (0..159), HL = Y (0..199)
CMASK EQU &B338 ;Address for colormask
;664/6128: &B6A3
FPLOT LD A, L ;A = Lowbyte Y
AND %00000111 ;isolate Bit 0..2
LD H, A ;= y MOD 8 to H
XOR L ;A = Bit 3..7 of Y
LD L, A ;= (Y\8)*8 to L
LD C, A ;store in C
LD B, &60 ;B = &C0\2 = Highbyte Screenstart\2
ADD HL, HL ;HL * 2
ADD HL, HL ;HL * 4
ADD HL, BC ;+ BC = Startaddress
ADD HL, HL ;of the raster line
SRL E ;calculate X\2, because 2 pixel per byte, Carry is X MOD 2
LD C, %10101010 ;Bitmask for MODE 0
JR NC, NSHIFT ;-> = 0, no shift
SHIFT LD C, %01010101 ;other bitmask for right pixel
NSHIFT ADD HL, DE ;+ HL = Screenaddress
LD A, (CMASK) ;get color mask
XOR (HL) ;XOR screenbyte
AND C ;AND bitmask
XOR (HL) ;XOR screenbyte
LD (HL), A ;new screenbyte
RET ;done
Fast plotting routine for MODE 1
This routine is approx. 6 times faster than the OS routine GRA PLOT, because it is dpendent to MODE 1 and doesn't perform range checks. It can draw 10500 pixels per second.
Input: DE = X (0..319), HL = Y (0..199)
CMASK EQU &B338 ;Address for colormask ;664/6128: &B6A3 FPLOT LD A, L ;A = Lowbyte Y AND %00000111 ;isolate Bit 0..2 LD H, A ;= y MOD 8 to H XOR L ;A = Bit 3..7 of Y LD L, A ;= (Y\8)*8 to L LD C, A ;store in C LD B, &60 ;B = &C0\2 = Highbyte Screenstart\2 ADD HL, HL ;HL * 2 ADD HL, HL ;HL * 4 ADD HL, BC ;+ BC = Startaddress ADD HL, HL ;of the raster line LD A, E ;Lowbyte X to A SRL D ;calculate X\4, because RR E ;4 pixel per byte SRL E ADD HL, DE ;+ HL = Screenaddress LD C, %10001000 ;Bitmask for MODE 1 AND %00000011 ;A = X MOD 4 JR Z, NSHIFT ;-> = 0, no shift SHIFT SRL C ;move bitmask to pixel DEC A ;loop counter JR NZ,SHIFT ;-position NSHIFT LD A, (CMASK) ;get color mask XOR (HL) ;XOR screenbyte AND C ;AND bitmask XOR (HL) ;XOR screenbyte LD (HL), A ;new screenbyte RET ;done
Fast plotting routine for MODE 2
And the MODE 2 routine. Perhaps this could be improved since there are only two colours, and the pixel shift may need to operate up to 7 times (so perhaps a table would average out better).
CMASK EQU &B338 ;Address for colormask
;664/6128 - &B6A3
FPLOT LD A, L ;A = Lowbyte Y
AND %00000111 ;isolate Bit 0..2
LD H, A ;= y MOD 8 to H
XOR L ;A = Bit 3..7 of Y
LD L, A ;= (Y\8)*8 to L
LD C, A ;store in C
LD B, &60 ;B = &C0\2 = Highbyte Screenstart\2
ADD HL, HL ;HL * 2
ADD HL, HL ;HL * 4
ADD HL, BC ;+ BC = Startaddress
ADD HL, HL ;of the raster line
LD A, E ;Lowbyte X to A
SRL D ;calculate X\8, because
RR E ;8 pixel per byte
SRL D
RR E
SRL E
ADD HL,DE ;+ HL = Screenaddress
LD C,%10000000 ;Bitmask for MODE 2
AND %00000111 ;A = X MOD 8
JR Z, NSHIFT ;-> = 0, no shift
SHIFT SRL C ;move bitmask to pixel
DEC A ;loop counter
JR NZ,SHIFT ;-position
NSHIFT LD A, (CMASK) ;get color mask
XOR (HL) ;XOR screenbyte
AND C ;AND bitmask
XOR (HL) ;XOR screenbyte
LD (HL), A ;new screenbyte
RET ;done