Difference between revisions of "Programming:Fast plot"

Revision as of 15:12, 24 August 2006

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		;Adress 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		;Adress 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		;Adress 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 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