# Cycles Procedural Square using Polar Coordinates

I'm using Blender 2.8 and trying to get a grasp on procedural textures. For fun, I was following through the list here at https://thndl.com/square-shaped-shaders.html and now I'm stuck.

Equation I'm trying to reproduce:

 float a=atan(c.x,c.y);

f=vec4(step(.5,cos( floor(a*.636+.5)* 1.57-a)*length(c.xy)))


Result = A Square

I have a feeling it has to do with the Polar Coordinates, but I'm not sure where considering I believe the math is correct everywhere else.

Can someone take a look and see where the mistake is and perhaps explain though it if possible?

Thanks!

Shader Node Setup: (Length = sqrt(x^2 + y^2)

The Result: I'm not sure what you've actually got wrong with your setup but I've tried to replicate it by entering your math into a Node Expressions expression (see https://baldingwizard.wixsite.com/blog/node-expressions) - which builds the nodes directly from the text.

This produces the following result : The generated 'inner' nodes for the 'f' function are : And here's the Blend file (Blender 2.8) for reference EDIT: Actually, I think I've spotted the error. Your nodes actually perform the calculation :

f = cos(floor(a * 0.636+0.5)*(1.57-a)) * dist


ie, Instead of multiplying by 1.57 and then subtracting 'a', you're nodes subtract a from 1.57 and then multiply - note the brackets I added around '1.57-a'). Here's the amended (wrong) calculation, replicating your result : • Hehe... just as i finished building the tree by hand, you nipped in before me! That'll teach me to use your kit.... Can I add 2 recommendations? – Robin Betts Oct 6 '19 at 9:28
• @RobinBetts Haha - sorry about that! :-) Sure can - always open to improvement. – Rich Sedman Oct 6 '19 at 9:30
• 1. It doesn't make a difference here, but the GLSL call is of the [-pi,pi] overload of atan(), so Arctan2 node would be a better choice, further down the page the OP is looking at. 2. Blender 2.81 provides a better Vector Math node for following GLSL whole-vector operations.. – Robin Betts Oct 6 '19 at 9:34
• @RobinBetts Thanks. The addon does actually support atan2 - yes, I probably should have used it (but as you say, not relevant here since it’s a square). I must admit to not really understanding the ‘vec4’ in the original expression - is that what you mean by ‘whole-vector’ operations? What’s that doing in this case? – Rich Sedman Oct 6 '19 at 9:41
• @RichSedman: Thanks so much! I made the adjustment and it turned out as it should. Also thanks for the link above! I'll be using that from now on to test. – Podis Oct 6 '19 at 11:25