From Newsgroup: comp.lang.forth

Can be used with any LINE command, as long as it draws a line between
two absolute coordinates. ( x1 y1 x2 y2 --):

: line cr rot >r -rot r> rot 0 .r ." ," . 0 .r ." ," . ; \ dummy line word

variable 'lineto \ stores
address of (lineto)

[: drop drop drop drop ;] constant (cancel) ( x1 y1 x2 y2 --)
[: 2dup 2>r line 2r> 'lineto @ ;] constant (lineto) ( x1 y1 x2 y2
-- x2 y2 xt)
[: 2dup (lineto) ;] constant (moveto) ( x y -- x y
x y xt)
: polygon[ ['] line (moveto) ; ( -- xt1 xt2)
: polyline[ (cancel) (moveto) ; ( -- xt1 xt2)
: +point rot execute ; ( x1 y1 xt x2
y2 -- x2 y2 xt)
: ]poly drop 2>r rot 2r> +point ; ( xt1 x1 y1
x2 y2 xt2 --)

(lineto) 'lineto !

This is a sample application:

polygon[ \ start a polygon
75 300 +point \ now issue all the points
161 329 +point
161 419 +point
215 347 +point
301 373 +point
250 300 +point
301 227 +point
215 253 +point
161 181 +point
161 271 +point
]poly \ close the polygon

All the points should be listed now (filtered output):

75,300 161,329 ok 6
161,329 161,419 ok 6
161,419 215,347 ok 6
215,347 301,373 ok 6
301,373 250,300 ok 6
250,300 301,227 ok 6
301,227 215,253 ok 6
215,253 161,181 ok 6
161,181 161,271 ok 6
75,300 161,271 ok

Hans Bezemer

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From Newsgroup: comp.lang.forth

On 10/09/2026 8:46 pm, Hans Bezemer wrote:

Can be used with any LINE command, as long as it draws a line between two absolute coordinates. ( x1 y1 x2 y2 --):

That was a 'star' effort! Never had the patience for graphics myself to it's good
to see someone else do it.

1 fload xplgraph

6 value color

: line ( x1 y1 x2 y2 --) 2swap moveto color line ; \ simulate using XPL graphics

\ General routine for a polyline or a polygon. H. Bezemer
\
\ Can be used with any LINE command, as long as it draws a line between
\ two absolute coordinates. ( x1 y1 x2 y2 --):

\ : line cr rot >r -rot r> rot 0 .r ." ," . 0 .r ." ," . ; \ dummy line word

variable 'lineto \ stores address of (lineto)

:noname drop drop drop drop ; constant (cancel) ( x1 y1 x2 y2 --)
:noname 2dup 2>r line 2r> 'lineto @ ; constant (lineto) ( x1 y1 x2 y2 -- x2 y2 xt)
:noname 2dup (lineto) ; constant (moveto) ( x y -- x y x y xt)
: polygon[ ['] line (moveto) ; ( -- xt1 xt2)
: polyline[ (cancel) (moveto) ; ( -- xt1 xt2)
: +point rot execute ; ( x1 y1 xt x2 y2 -- x2 y2 xt)
: ]poly drop 2>r rot 2r> +point ; ( xt1 x1 y1 x2 y2 xt2 --)

(lineto) 'lineto !

$12 SetVid \ 640x480x16

polygon[ \ start a polygon
75 300 +point \ now issue all the points
161 329 +point
161 419 +point
215 347 +point
301 373 +point
250 300 +point
301 227 +point
215 253 +point
161 181 +point
161 271 +point
]poly \ close the polygon

key drop \ admire

$03 SetVid \ text mode


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From Newsgroup: comp.lang.forth

Ed, I only say this:

variable (color)

: set_pixel (color) @ ;

And I'll think you'll have circles, ellipses, arcs and bezier curves in
no time flat ;-)

Hans Bezemer

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From Newsgroup: comp.lang.forth

On 10-09-2026 19:22, Hans Bezemer wrote:
In my enthusiasm I had completely overlooked that 4tH is 32/64-bit and DX-Forth is 16-bit. I tried arc-circles, bezier curves -- I never even
tried ellipses, because these require double words in 32-bit 4tH to
begin with, so -- no chance of winning.

But! At least you now got circles as well ;-) (Yeah, I tried!)

Hans Bezemer

---8<---
: circle ( x y radius --)
swap >r swap >r 1 over - swap 0 ( dp x y R: x0 y0)

begin
over r@ + over r> r@ swap >r + color point ( x0 + x,
y0 + y)
over r@ swap - over r> r@ swap >r + color point ( x0 - x,
y0 + y)
over r@ + over r> r@ swap >r swap - color point ( x0 + x,
y0 - y)
over r@ swap - over r> r@ swap >r swap - color point ( x0 - x,
y0 - y)
over r> r@ swap >r + over r@ + swap color point ( x0 + y,
y0 + x)
over r> r@ swap >r + over r@ swap - swap color point ( x0 - y,
y0 + x)
over r> r@ swap >r swap - over r@ + swap color point ( x0 + y,
y0 - x)
over r> r@ swap >r swap - over r@ swap - swap color point ( x0 - y,
y0 - x)
( dp x y R: x0 y0)
1+ >r over 0> if 1- r@ over - else r@ then 2* 1+ rot + swap r>
over over < ( dp x y f R: x0 y0)
until drop drop drop r> drop r> drop
;
---8<---
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From Newsgroup: comp.lang.forth

On 11/09/2026 9:30 pm, Hans Bezemer wrote:

On 10-09-2026 19:22, Hans Bezemer wrote:
In my enthusiasm I had completely overlooked that 4tH is 32/64-bit and DX-Forth is 16-bit. I tried arc-circles, bezier curves -- I never even tried ellipses, because these require double words in 32-bit 4tH to begin with, so -- no chance of winning.

But! At least you now got circles as well ;-) (Yeah, I tried!)

1 fload xplgraph

$12 SetVid \ 640x480x16

6 value color

xmax 2/ ymax 2/ 100 circle

key drop

$03 SetVid

Too easy ;)

Circle only took 6 mS to draw under DOSBOX. Tried it with BGI graphics
and it was 8 mS. The BGI is all machine code so if it were going to be
better, I'd expect to see that reflected.
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From Newsgroup: comp.lang.forth

On 12/09/2026 1:04 am, dxf wrote:

On 11/09/2026 9:30 pm, Hans Bezemer wrote:

On 10-09-2026 19:22, Hans Bezemer wrote:
In my enthusiasm I had completely overlooked that 4tH is 32/64-bit and DX-Forth is 16-bit. I tried arc-circles, bezier curves -- I never even tried ellipses, because these require double words in 32-bit 4tH to begin with, so -- no chance of winning.

But! At least you now got circles as well ;-) (Yeah, I tried!)

1 fload xplgraph

$12 SetVid \ 640x480x16

6 value color

xmax 2/ ymax 2/ 100 circle

key drop

$03 SetVid

Too easy ;)

Circle only took 6 mS to draw under DOSBOX. Tried it with BGI graphics
and it was 8 mS. The BGI is all machine code so if it were going to be better, I'd expect to see that reflected.

The bottleneck was the Borland EGAVGA BGI driver. Substituting a third-party SVGA BGI driver, the time dropped to 1 mS. IIRC things like Circle weren't typically handled in the driver but emulated in the graphics library. In the case of the SVGA BGI circle was handled internally and plainly faster. Even so, the performance of forth-based Circle is still very respectable.

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From Newsgroup: comp.lang.forth

On 11-09-2026 18:34, dxf wrote:

Circle only took 6 mS to draw under DOSBOX. Tried it with BGI graphics
and it was 8 mS. The BGI is all machine code so if it were going to be
better, I'd expect to see that reflected.

The bottleneck was the Borland EGAVGA BGI driver. Substituting a third-party SVGA BGI driver, the time dropped to 1 mS. IIRC things like Circle weren't typically handled in the driver but emulated in the graphics library. In the case of the SVGA BGI circle was handled internally and plainly faster. Even so, the performance of forth-based Circle is still very respectable.

I used the Midpoint Circle Algorithm. It's FAST! Instead of using
expensive floating-point arithmetic or trigonometric functions, it
relies entirely on fast integer addition and subtraction to calculate
pixel coordinates.

I've seen the performance of a z80 assembly version on a ZX Spectrum,
compared to the ROM routine. It takes a minute to run the ROM version --
and a second(!) or so for the MCA. So yes, I do have an expensive taste
when it comes to graphical algorithms! ;-)

Have fun!

Hans Bezemer

https://www.youtube.com/watch?v=sdccAInujFU
Second half is the MCA.

Z80 snapshot: https://github.com/ibancg/zxcircle/blob/master/zxcircle.z80
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