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Gury

Moj Mikro magazine listings: Super fast circle routine

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I present you super fast routine for drawing circles in graphics mode 8 and 8 + 16.

 

Moj Mikro magazine article listings are available as zipped file in download section. It contains ATR disk image file with Atari DOS system for using with disk based, real Atari machine or any Atari 8-bit emulator. To load Atari BASIC programs properly, Atari must be powered with Atari BASIC enabled, or you can try them with any compatible BASIC.

 

mojmikro_logo.png

 

You can try, use and modify the programs and routines for whatever purpose you want.

 

Super Fast Circle Routine

 

Magazine: Moj Mikro, 1989/3

Author : Zlatko Bleha

Page : 27 - 31

Article link

Atari BASIC listing on disk (tokenized): M8903284.BAS

Atari BASIC listing (listed): M8903284.LST

Assembly language listing: CIRCLE.LST

 

This routine uses very fast algorithm for drawing circles. It works in graphics mode 8. To see it in action, try the following demonstration program, which includes circle routine in DATA tables for using it from Atari BASIC. Also included is assembly language source code for anybody to examine inner workings of the algorithm. It is written in ATMAS 2.

 

circles_5.png circles_6.png circles_7.png circles_10.png circles_12.png

 

Description

 

Algorithm is based on one from Croatian computer magazine Racunari (number 31). There is a little faster way of doing this, but data must be provided in tables for sine and cosine. But this alternative takes more RAM.

 

The routine consists of two parts: main program for calculating X and Y coordinates and second part with PLOT routine for drawing (or erasing) pixels on X and Y coordinates. Calculation of coordinates is done for one eighth of the circle. Other seven parts are simply mirrored from original mentioned pattern. We take advantage of this fact, because circle is simetricly shaped. The routine uses Page Zero locations for variables for even faster execution. There are 17 of them.

 

Usage of the routine

 

A=USR(30000,POK,X,Y,R)

 

30000 - Starting address of the calling routine

POK - 1 (draw the circle), 0 (erase the circle)

X - X coordinate of the circle

Y - Y coordinate of the circle

R - Radius of the circle

 

The routine is not relocatable. If you want to relocate it anyway, use assembler of your choice and assemble it to another location or amend the DATA tables in Atari BASIC program demonstration.

 

Maximum value for radius is 127, which is more than enough, because the circle with such radius will not be seen on the screen in whole anyway. If you choose wrong parameter values and consequently break the borders of the screen, don't worry, circle will be drawn anyway, but with its parts in different places. Experiment with the values for best results and your own fun.

 

The included assembly language listing shows what is necessary for implementing circle algorithm, calculating coordinates and drawing pixels and circles on the screen.

 

 

Fast circle drawing in pure Atari BASIC

 

Magazine: Moj Mikro, 1989/3

Author : Zlatko Bleha

Page : 27 - 31

Atari BASIC listing on disk (tokenized): M8903282.BAS

Atari BASIC listing (listed): M8903282.LST

 

Next example is demonstration of implementing mentioned circle algorithm in pure Atari BASIC. This program shows how much faster it is compared to classic program using sine and cosine functions from Atari BASIC (shown in last example).

 

circles_2.png circles_3.png circles_4.png

 

Use some valid values for coordinates and radius, for example:

 

X=40, Y=40, R=30

X=130, Y=90, R=60

 

Slow circle drawing in Atari BASIC

 

Magazine: Moj Mikro, 1989/3

Author : Zlatko Bleha

Page : 27 - 31

Atari BASIC listing on disk (tokenized): M8903281.BAS

Atari BASIC listing (listed): M8903281.LST

 

This is classic example for drawing circles from Atari BASIC using sine and cosine functions. Unfortunatelly, this is very slow way of doing it and not recommended. Just use routine shown above and everybody will be happy :)

 

circles_1.png

 

Conclusion

 

Returning back to first program with the fastest way of drawing circles... There is one more thing to note. In case you want to use PLOT subroutine, which is part of the main circle routine, then read following explanation.

 

PLOT routine is written so it can be used easily from Atari BASIC program independently from main circle routine, by using like this:

 

A=USR(30179,POK,X,Y)

 

POK - 1 (drawing a pixel), 0 (erasing a pixel)

X - X coordinate of the pixel

Y - Y coordinate of the pixel

 

The routine alone is not any faster than normal PLOT command from Atari BASIC, because USR command takes approximatelly 75% of whole execution. But, used as part of the main circle routine it does not matter anymore, because it is integrated in one larger entity. There the execution is very fast, with no overhead. PLOT routine is here for you to examine anyway. You never know if you will maybe need it in the future.

 

Greetings,

Gury

Super fast circle routine.zip

Edited by Gury

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I present you super fast routine for drawing circles in graphics mode 8 and 8 + 16.

 

[...]

 

Greetings,

Gury

 

Hello Gury,

 

thanks for posting this, this is very useful stuff!

 

-- Carsten

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You are welcome, Cas, and thank you. I hope people will make good use of the routine and have some fun.

 

I mistakely uploaded listed files as binary files. I will fix the problem when I come home. Anyway, here are the listings for you to look at.

 

M8903284.LST

 

1 REM *******************************
2 REM PROGRAM : SUPER FAST CIRCLE ROUTINE
3 REM AUTHOR : ZLATKO BLEHA
4 REM PUBLISHER: MOJ MIKRO MAGAZINE
5 REM ISSUE NO.: 1989, NO.3, PAGE 28
6 REM *******************************
7 REM 
10 FOR A=30000 TO 30288
20 READ B:C=C+B:POKE A,B
30 NEXT A
40 IF C<>28218 THEN ? "*** DATA ERROR ***":END 
50 DATA 120,104,104,104,133,58,104,133,51,133
60 DATA 60,104,133,50,133,59,104,104,168,133
70 DATA 54,104,104,208,5,152,88,76,242,117
80 DATA 133,56,56,233,1,133,55,160,0,132
90 DATA 57,165,59,24,101,57,133,50,152,101
100 DATA 60,133,51,165,54,101,56,133,61,32
110 DATA 242,117,165,54,56,229,56,133,62,32
120 DATA 242,117,165,59,56,229,57,133,50,165
130 DATA 60,233,0,133,51,165,62,32,242,117
140 DATA 165,61,32,242,117,165,59,24,101,56
150 DATA 133,50,152,101,60,133,51,165,54,101
160 DATA 57,133,63,32,242,117,165,54,56,229
170 DATA 57,133,64,32,242,117,165,59,56,229
180 DATA 56,133,50,165,60,233,0,133,51,165
190 DATA 64,32,242,117,165,63,32,242,117,230
200 DATA 57,165,55,56,229,57,229,57,16,7
210 DATA 198,56,24,101,56,101,56,133,55,165
220 DATA 56,197,57,48,3,76,89,117,96,104
230 DATA 104,104,133,58,104,133,51,104,133,50
240 DATA 104,104,160,0,132,49,133,48,10,38
250 DATA 49,10,38,49,24,101,48,170,152,101
260 DATA 49,133,49,138,10,38,49,10,38,49
270 DATA 10,38,49,24,101,88,133,48,165,49
280 DATA 101,89,133,49,166,51,134,53,165,50
290 DATA 170,70,53,106,70,53,106,70,53,106
300 DATA 24,101,48,133,48,165,53,101,49,133
310 DATA 49,138,41,7,170,152,56,106,202,16
320 DATA 252,166,58,240,6,17,48,145,48,88
330 DATA 96,73,255,49,48,145,48,88,96
500 REM ***************************
501 REM * DEMONSTRATION PROGRAM *
502 REM ***************************
503 REM 
510 GRAPHICS 8:SETCOLOR 2,0,0:COLOR 3
520 FOR A=2 TO 90
530 Q=USR(30000,1,A,A,A)
540 Q=USR(30000,1,319-A,A,A)
550 NEXT A
560 ? "PRESS ANY KEY TO CONTINUE"
570 IF PEEK(555)=0 THEN 570
580 ?  :? :FOR A=2 TO 90
590 Q=USR(30000,1,319-A,159-A,A)
600 Q=USR(30000,1,A,159-A,A)
610 NEXT A
620 ? "PRESS ANY KEY TO CONTINUE"
630 IF PEEK(555)=0 THEN 630
640 GRAPHICS 8:SETCOLOR 2,0,0:COLOR 3
650 FOR A=2 TO 79 STEP 4
660 Q=USR(30000,1,100,A,A)
670 NEXT A
680 FOR A=82 TO 2 STEP -4
690 Q=USR(30000,1,A+100,A,A)
700 NEXT A
710 ? "PRESS ANY KEY TO START AGAIN"
720 IF PEEK(555)=0 THEN 720
730 GOTO 510

 

M8903282.LST

 

1 REM *******************************
2 REM PROGRAM : FAST CIRCLE DRAWING
3 REM AUTHOR : ZLATKO BLEHA
4 REM PUBLISHER: MOJ MIKRO MAGAZINE
5 REM ISSUE NO.: 1989, NO.3, PAGE 29
6 REM *******************************
7 REM 
10 GRAPHICS 8:SETCOLOR 2,0,0:COLOR 3
20 ? "ENTER X, Y AND R"
30 INPUT X,Y,R
40 IF R=0 THEN PLOT X,Y:END 
50 B=R:C=0:A=R-1
60 PLOT X+C,Y+B
70 PLOT X+C,Y-B
80 PLOT X-C,Y-B
90 PLOT X-C,Y+B
100 PLOT X+B,Y+C
110 PLOT X+B,Y-C
120 PLOT X-B,Y-C
130 PLOT X-B,Y+C
140 C=C+1
150 A=A+1-C-C
160 IF A>=0 THEN 190
170 B=B-1
180 A=A+B+B
190 IF B>=C THEN 60

 

M8903281.LST

 

1 REM *******************************
2 REM PROGRAM : SLOW CIRCLE DRAWING
3 REM AUTHOR : ZLATKO BLEHA
4 REM PUBLISHER: MOJ MIKRO MAGAZINE
5 REM ISSUE NO.: 1989, NO.3, PAGE 29
6 REM *******************************
7 REM 
10 GRAPHICS 8:SETCOLOR 2,0,0:COLOR 3
20 FOR A=0 TO 6.28 STEP 0.02
30 X=SIN(A)*50+150
40 Y=COS(A)*50+80
50 PLOT X,Y
60 NEXT A

 

CIRCLE.LST

 

*
* FAST CIRCLE DRAWING ROUTINE
* 
* Author : Zlatko Bleha
* Publisher: Moj Mikro magazine
* Issue No.: 1989, No.3, Page 27
*
* -----------------------------
* System variables on Page Zero
* -----------------------------
*
LO	EQU $30
HI	EQU $31
XLO EQU $32
XHI EQU $33
XLOH EQU $34
XHIH EQU $35
Y 	EQU $36
A 	EQU $37
B 	EQU $38
C 	EQU $39
POK EQU $3A
X1	EQU $3B
X2	EQU $3C
YVIB EQU $3D
YMAB EQU $3E
YVIC EQU $3F
YMAC EQU $40
*
* -----------------------------------
* Taking circle parameters from stack
* -----------------------------------
*
	ORG $7530
	SEI
	PLA
	PLA
	PLA
	STA POK
	PLA
	STA XHI
	STA X2
	PLA
	STA XLO
	STA X1
	PLA
	PLA
	TAY
	STA Y
	PLA
	PLA
	BNE NEXT
	TYA
	CLI
	JMP PLOT
NEXT STA B
	SEC
	SBC #$1
	STA A
	LDY #$0
	STY C
*
* -----------------------------
* PLOT X+C,Y+B
* -----------------------------
*
LOOP LDA X1
	CLC
	ADC C
	STA XLO
	TYA
	ADC X2
	STA XHI
	LDA Y
	ADC B
	STA YVIB
	JSR PLOT
*
* -----------------------------
* PLOT X+C,Y-B
* -----------------------------
*
	LDA Y
	SEC
	SBC B
	STA YMAB
	JSR PLOT
*
* -----------------------------
* PLOT X-C,Y-B
* -----------------------------
*
	LDA X1
	SEC
	SBC C
	STA XLO
	LDA X2
	SBC #$0
	STA XHI
	LDA YMAB
	JSR PLOT
*
* -----------------------------
* PLOT X-C,Y+B
* -----------------------------
*
	LDA YVIB
	JSR PLOT
*
* -----------------------------
* PLOT X+B,Y+C
* -----------------------------
*
	LDA X1
	CLC
	ADC B
	STA XLO
	TYA
	ADC X2
	STA XHI
	LDA Y
	ADC C
	STA YVIC
	JSR PLOT
*
* -----------------------------
* PLOT X+B,Y-C
* -----------------------------
*
	LDA Y
	SEC
	SBC C
	STA YMAC
	JSR PLOT
*
* -----------------------------
* PLOT X-B,Y-C
* -----------------------------
*
	LDA X1
	SEC
	SBC B
	STA XLO
	LDA X2
	SBC #$0
	STA XHI
	LDA YMAC
	JSR PLOT
*
* -----------------------------
* PLOT X-B,Y+C
* -----------------------------
*
	LDA YVIC
	JSR PLOT
* -----------------------------
	INC C
	LDA A
	SEC
	SBC C
	SBC C
	BPL JUMP
	DEC B
	CLC
	ADC B
	ADC B
JUMP STA A
	LDA B
	CMP C
	BMI END
	JMP LOOP
END RTS
*
* -----------------------------
* PLOT routine
* -----------------------------
*
* ------------------------------------
* Taking parameters from stack in case
* PLOT routine is called directly from
* BASIC
* ------------------------------------
*
	PLA
	PLA
	PLA
	STA POK
	PLA
	STA XHI
	PLA
	STA XLO
	PLA
	PLA
	LDY #$0
*
* -----------------------------
* Beginning of the PLOT routine
* -----------------------------
*
* Calculating A*40
* -----------------------------
*
PLOT STY HI
	STA LO
	ASL
	ROL HI
	ASL
	ROL HI
	CLC
	ADC LO
	TAX
	TYA
	ADC HI
	STA HI
	TXA
	ASL
	ROL HI
	ASL
	ROL HI
	ASL
	ROL HI
*
* -----------------------------
* A*40+VIDEO
* -----------------------------
*
	CLC
	ADC $58
	STA LO
	LDA HI
	ADC $59
	STA HI
*
* -----------------------------
* X/8
* -----------------------------
*
	LDX XHI
	STX XHIH
	LDA XLO
	TAX
	LSR XHIH
	ROR
	LSR XHIH
	ROR
	LSR XHIH
	ROR
*
* -----------------------------
* A*40+VIDEO+X/8
* -----------------------------
*
	CLC
	ADC LO
	STA LO
	LDA XHIH
	ADC HI
	STA HI
*
* -----------------------------
* Calculating a location of
* destination bit
* -----------------------------
*
	TXA
	AND #$7
	TAX
	TYA
	SEC
ROT ROR
	DEX
	BPL ROT
*
* -----------------------------
* PLOT or UNPLOT?
* -----------------------------
*
	LDX POK
	BEQ UNPLOT
*
* -----------------------------
* PLOT
* -----------------------------
*
	ORA (LO),Y
	STA (LO),Y
	CLI
	RTS
*
* -----------------------------
* UNPLOT
* -----------------------------
*
UNPLOT EOR #$FF
	AND (LO),Y
	STA (LO),Y
	CLI
	RTS
* -----------------------------

 

 

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