translate to the center of the rectangle, rotate and translate back

there are two ways

One is to calculate the points yourself and draw, which is painful

But here is a useful snippet

(q/with-translation [(+ x half-width) (+ y half-height)]
  (q/rotate angle)
  (q/translate (- half-width) (- half-height))
  (q/rect 0 0 width height))

Thank you all. It seems to be quite a chore for such a simple operation ) Is there anything standard in the core quil lib? I guess might others have the same question

Get used to it :) It works this way in most of such libraries. With rotate/translate/scale/shear you build affine transformation of your plane. This way shapes and tranformations are separated and can be composed.

I highly recommend drawing by hand until you get a hang of it, it becomes a lot easier then

Alternately, you can use the center rect-mode and it’ll save you one translate call…

The problem with translation is that I need to know the actual coordinates of a primitive, before rotation, every time. This is not helpful when drawing within mapv or similar AND it does not work for ellipse..

@U8VE0UBBR Can you elaborate on the center mode, can't find it in the api

http://quil.info/api/shape/attributes#rect-mode

It controls how arguments to rect are interpreted. It doesn't affect the rotation point though.

Great, that helps a bit. What about other shapes, like triangle and vertex?

Only ellipse (`ellipse-mode`) is supported. Regardings triangle, there are more than 70k of definitions of triangle https://faculty.evansville.edu/ck6/encyclopedia/ETC.html... The same probably applies to any other (not symmetrical) shape.

Generally you may want to find a center of the shape enclosing circle. But it's not trivial in general.

The simplest solution so far for me is to use (q/with-translation [] (q/with-rotation [] combo, with the :center mode. But the triangles are off as expected, as you can see on the image, returned by a mapv sequence.

Here it's more clear : )

Depends what you expect. And how you define the center of the triangle.

What about inducing the size of the rectangle surrounding a shape and rotating it/the whole canvas in closure?

Doable. If you are on JDK, take a look at PShape which knows enclosing box size.

https://processing.org/reference/PShape.html

If I understand you correctly, I can use Pshape with quil via interop, right?

I am not bit on java interop, how can I access it?

Hmmm... In Processing you cal call createShape I don't see such function in quil. It's explained here: https://github.com/quil/quil/issues/165

Maybe the easiest way is to calculate the centroid of used vertices and rotate around it. Centroid is just an average of point coordinates (x and y separately).

Thanks everyone for help!