ETUDES
(C) Urzha Andrew
Cheboksary, 1996.
The procedure for drawing a circle.
I suggest you the procedure for drawing a circle (much
faster than the standard CIRCLE).
In the register pair HL recorded coordinates of the center,
and in case D - the radius of the circle. 140.
ORG 50000
LD HL, 87 * 256 127
And 87 - Y, 127 - X
LD D, 50
; R
LD C, 0
LD B, D
LOOP CALL PLOT
LD A, B
NEG
LD B, A
CALL PLOT
LD A, C
NEG
LD C, A
CALL PLOT
LD A, B
NEG
LD B, A
CALL PLOT
LD A, C
LD C, B
LD B, A
CALL PLOT
LD A, C
NEG
LD C, A
CALL PLOT
LD A, B
NEG
LD B, A
CALL PLOT
LD A, C
NEG
LD C, A
CALL PLOT
LD A, C
LD C, B
LD B, A
INC C
LD A, D
SUB C
LD D, A
JR NC, LOOP
DEC B
LD A, D
ADD A, B
LD D, A
LD A, B
CP C
JR NC, LOOP
RET
PLOT PUSH DE
PUSH BC
PUSH HL
LD A, H
ADD A, B
LD B, A
LD A, L
ADD A, C
LD C, A
CALL # 22E5
POP HL
POP BC
POP DE
RET
2
The length of the procedure, 93 bytes.
The idea is taken from the ZX-FORUM 3. Not
doubt that the procedure can be
much easier (especially the first part). Also there is a
limitation - you can not specify the radius zero.
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