Dilla's Scripting Blunders

From wikipedia:

Quote
Many programming languages also provide the two-argument atan2 function, which computes the arctangent of y / x given y and x, but with a range of (−π, π].

You'll have to do a loop if you want a larger range, I think.

radialCoordinate = math.log(math.sqrt ( x^2 + y^2 ) * 30)
angularCoordinate = 0.5 + math.atan2 (x,y) / (2 * math.pi)
spiralGrd = angularCoordinate + radialCoordinate
spiralGrd = spiralGrd - math.floor(spiralGrd)

route spiralGrd to the output and take a look

Well, I supplied the the code as a starting point. As such it does not make sense to have aa-zones for a gradient (there are no zones...). If you use the gradient to create that threshold like output, it makes sense to use the conditional ("if..then..else") to determine the aa_zone.

you can try using this as aa_zone though: math.floor(spiralGrd * 3), where 3 is the multiplication constant from the radialCoordinate calculation / 10. This should reduce moire aliasing in the center region, while skipping aa calc in the soft large gradients

For the centering you need to think "reverse", i.e. subtract 0.5 from x and y initially so you have 0,0 in the visual center region.

Is that a spiral formula Sphinx? If i try to center the XY positions by subtracting a 0.5 value i get more of a radial remapped result from the input.

function prepare()
end;

function get_sample(x, y)

radialCoordinate = math.log(math.sqrt ((x-0.5)^2 + (y-0.5)^2 ) * 30)
angularCoordinate = 0.5 + math.atan2 (x,y) / (2 * math.pi)
spiralGrd = angularCoordinate + radialCoordinate
spiralGrd = spiralGrd - math.floor(spiralGrd)

r,g,b,a = get_sample_map(spiralGrd, spiralGrd, SOURCE)
return r, g, b, a
end;

Thanks, it seems no different doing that though. Testing with just a basic gradient to make things more visible i can see rings rather than a spiral -

function prepare()
end;

function get_sample(x, y)

radialCoordinate = math.log(math.sqrt ((x-0.5)^2 + (y-0.5)^2 ) * 30)
angularCoordinate = 0.5 + math.atan2 (x,y) / (2 * math.pi)
spiralGrd = angularCoordinate + radialCoordinate
spiralGrd = spiralGrd - math.floor(spiralGrd)

return spiralGrd, spiralGrd, spiralGrd, 1
end;

Or is that how it's suppose to be?

Oh I get it now James well I meant:

add this as the first thing in the script, then you don't have to think more about it.

x,y = x - 0.5, y - 0.5

This is so much fun! I couldn't resist turning this into a full-featured Spiral Gradient component. Submission to the library pending...

Take a look... constructive criticism on code optimization (and the AA_zones hack) is very welcome, cause - you know - it'll learn me.

Also, I'm thinking about adding a 'Fixed Size' option.

Spiral Gradient.ffxml

Oh, I just realized that there is an even better aa_zone to return.

Find the line:

spiralGrd = spiralGrd - math.floor(spiralGrd)

and replace that with

aa_zone = math.floor(spiralGrd)
spiralGrd = spiralGrd - aa_zone

and ensure that aa_zone is not modified afterwards by old script etc..

One useful thing might be to maybe add the new Bezier curve control so the user could shape the profile with a custom curve.

Code wise everything seems quite good also.

Quote
With Size, pixels at 1 the script throws an error. Hmmm!?....

Function math.log(x) returns nil value at x<=0.
By such a reason, the value of spiralGrd has been nil value at center coordinate.

It is necessary to rewrite so that zero must not be parameter of math.log().

For example

Code
-- calculate spiral gradient map    radialCoordinate = math.log (math.sqrt ( spiralX*spiralX + spiralY*spiralY )) * windings

rewrite like this

Code
-- calculate spiral gradient map    local radial = math.sqrt ( spiralX*spiralX + spiralY*spiralY )    radial = math.max(radial, 0.00001)    radialCoordinate = math.log (radial) * windings

Oh my, there sure are some interesting polygon hit-test algorithms out there -- exciting stuff to dig into...

http://paulbourke.net/geometry/insidepoly/

Looks like my next scripting assignment is porting one of these to Lua. Personally, I'd choose the first one...

Ghislaine,

unfortunately I'm currently swamped in a project -- which means no time for filter authoring fun. However, feel free to post your suggestions here, and I might look into it once things have calmed down at work.

Hi dear !

I do not remember either.

Glad to get news from you. Have a nice day my friend.