Understanding ui.Transform.rotation

[Phuket2]

Sorry, I am sure this is just such a stupid question. But I don't get how ui.Transform.rotate works. I put an example below. Naively, I thought that the rotation would just pivot around the center point of the rect. But it clearly does not.
Any help appreciated

import ui

class MyClass(ui.View):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        
    def draw(self):
        s = ui.Path.rect(100, 100, 200, 200)
        with ui.GState():
            ui.set_color('deeppink')
            s.fill()
            
        with ui.GState():
            ui.concat_ctm(ui.Transform.rotation(.45))
            ui.set_color('red')
            s.fill()
            

if __name__ == '__main__':
    w = 600
    h = 800
    f = (0, 0, w, h)
    mc = MyClass(frame = f, bg_color = 'white')
    mc.present('sheet')

[Phuket2]

Should have attached a pic before 😱
But you can see the rotation is not Center based.

[omz]

Rotation is around the origin (0, 0) by default. To rotate your drawing around an arbitrary point, you have to combine the rotation with a translation, like this:

import ui

class MyClass(ui.View):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        
    def draw(self):
        s = ui.Path.rect(100, 100, 200, 200)
        with ui.GState():
            ui.set_color('deeppink')
            s.fill()
            
        with ui.GState():
            # Move the origin (0, 0) to the center of the rectangle:
            ui.concat_ctm(ui.Transform.translation(200, 200))
            # Rotate the coordinate system:
            ui.concat_ctm(ui.Transform.rotation(.45))
            # Move the origin back, so that the rectangle's coordinates are valid:
            ui.concat_ctm(ui.Transform.translation(-200, -200))
            ui.set_color('red')
            s.fill()

if __name__ == '__main__':
    w = 600
    h = 800
    f = (0, 0, w, h)
    mc = MyClass(frame = f, bg_color = 'white')
    mc.present('sheet')

[Phuket2]

@omz, thanks a lot.
I did the below, I could not apply a unary operator - to the unpacking. Not sure it's possible or not. Would have been nicer 😱

import ui

class MyClass(ui.View):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        
    def draw(self):
        rect = ui.Rect(100, 100, 300, 400)
        s = ui.Path.rect(*rect)
        with ui.GState():
            ui.set_color('deeppink')
            s.fill()
            
        with ui.GState():
            # Move the origin (0, 0) to the center of the rectangle:
            ui.concat_ctm(ui.Transform.translation(*rect.center()))
            #ui.concat_ctm(ui.Transform.translation(200, 200))
            # Rotate the coordinate system:
            ui.concat_ctm(ui.Transform.rotation(.45))
            # Move the origin back, so that the rectangle's coordinates are valid:
            #ui.concat_ctm(ui.Transform.translation(*rect.center()))
            ui.concat_ctm(ui.Transform.translation(-rect.center()[0], -rect.center()[1]))
            ui.set_color('red')
            s.fill()
            
if __name__ == '__main__':
    w = 600
    h = 800
    f = (0, 0, w, h)
    mc = MyClass(frame = f, bg_color = 'white')
    mc.present('sheet')

[omz]

@Phuket2 While you cannot use the unary minus operator with points or tuples, this should work, and is a bit more concise: ui.Transform.translation(*(rect.center() * -1))

[Phuket2]

@omz, thanks. Simple, but you have to understand better than I do how the values are unpacked. In a few more years it will come to me, hopefully 😱