How to make a window/picture/button with rounded corners?

How to make a window/picture/button with rounded corners?

Not sure that will fit 100% to your question but maybe use can use Urho2DStretchableSprite for your case.
Code here: https://github.com/urho3d/Urho3D/tree/master/Source/Samples/51_Urho2DStretchableSprite

you can hack the default style ui texture

Yes, I guess what @Leith said is much simpler. Just make your own version of https://github.com/urho3d/Urho3D/blob/master/bin/Data/Textures/UI.png and use it in your style instead of the default one.

Look here to find out where exactly the rectangles are defined: https://github.com/urho3d/Urho3D/blob/master/bin/Data/UI/DefaultStyle.xml
Without knowing I guess:

    <element type="Button" style="BorderImage">
        <attribute name="Image Rect" value="16 0 32 16" />
        <attribute name="Border" value="4 4 4 4" />
        <attribute name="Pressed Image Offset" value="16 0" />
        <attribute name="Hover Image Offset" value="0 16" />
        <attribute name="Pressed Child Offset" value="-1 1" />
    </element>
...
    <element type="Window" style="BorderImage">
        <attribute name="Image Rect" value="48 0 64 16" />
        <attribute name="Border" value="4 4 4 4" />
        <attribute name="Resize Border" value="8 8 8 8" />
    </element>

relax dude, take your time lol, I’m pretty easy to talk to

when I was 8, I won a scholarship to a private school, it had ethernet 1.0, and computers were talking to each other, so I hacked the network, demoted all the staff, and they kicked me out without any proof. This was a milestone for me, and a millstone, you know? The one that hangs around your neck for life.

There are no markers indicating edited text that would make that even tangentially related … maybe don’t derail so much?

Tangent derails no one cares … but this is off in “I’ve been bird-watching for 10 years, was subjected to a plagiarism inquiry writing about a subject I’m as knowledgeable as experts because my paper was too good” in response to “ I’m struggling with finding the volume of my closed quadratic patch shapes ” land. Too much derail, use gitter or IRC for that.

yeah my bad, I apologize profusely