Drawing: Rotation of a shape around an origin

[CodeCox]

RE: Rotations in new Transform feature

I was hoping that you could shed some light on a problem I am having while playing wIth the 2D Orbits examples in demo.py and in the doc.

A minimal scenario involves me just changing the circle shape to a square shape. I kinda simply replace draw_circle with draw_rectangle. I now expect to have square planets & moons orbiting around their origins. But contrary to my expectations, the square shape does not exhibit the same behaviour as the circle shape. Unlike the circle shape, the square shape seems to have an additional rotation, This seems inconsistent to me - I'm thinking that both the shapes should reflect the same movement. See screenshot of a minimal example illustrating my dilemma.

Why? What am I misunderstanding about these transforms?

How do I use square shapes as planets instead of circles shapes?

Screenshot

Code

import math
import dearpygui.dearpygui as dpg

dpg.create_context()
dpg.create_viewport(title='Rotation', width=400, height=400)
dpg.setup_dearpygui()

with dpg.viewport_drawlist(front=True, tag="vpf"):
    with dpg.draw_node(tag="origin"):
        dpg.apply_transform("origin", dpg.create_translation_matrix((50, 300)))
        dpg.draw_circle((0, 0), 5, fill=(255, 255, 255))
        dpg.draw_text((10, 0), 'origin', size=16)
        for rot in [0.0, 30.0,45.0,60.0,90.0]:
            with dpg.draw_node():
                dpg.apply_transform(dpg.last_item(),
                    dpg.create_rotation_matrix(math.pi * rot/180.0, [0,0,-1]) * dpg.create_translation_matrix((200,0)))
                dpg.draw_rectangle((0, 0), (40, 40))
                dpg.draw_circle((0, 0), 20)
                dpg.draw_text((45, 45), rot, size=16)

dpg.show_viewport()
dpg.start_dearpygui()
dpg.destroy_context()

[hoffstadt]

Hi, we probably should have documented this better.

The transforms are acting on the points you input. For rectangle, the transforms are applying to pmin and pmax. Which is what you are seeing.

For what I believe you are trying to do, you should be using dpg.draw_quad(...). Quads require you to input all 4 points, which when transformed, will give the effect you are looking for.

[CodeCox]

Thanks , draw_quad did the trick! Yes, its now working as I expect for my minimal example!

Now I need to understand how the transforms work on the different method signatures - but that's an exercise for another day! (Any updates to the docs will be appreciated.)

Ciao