Want to create a radial gradient with start circle and end circle are the same, but not working, the test code is the same with cairo default test code
Can you provide additional details about what is not working?
In particular, the backend you are using, the cairo revision and the result vs the expected result.
The expected result for a degenerate radial gradient like the one you are describing should be a transparent pattern.
Created attachment 45035 [details]
Result I excepted
To get that result, the two extreme circles shoud *not* be the same.
The documentation is quite lacking, but you can find the definition of the radial gradients here:
You probably wanted to do something like cairo_pattern_create_radial(rx,ry,r,rx,ry,0).