The function adds Radial Line Gradation. You can also make a shape by changing the contrast and number.
Prepare an illustration.
Open ①Layer window and add ②New Layer .
Tap ②Filter from ①Tool Selection window .
Tap ①Radial Line Gradation .
Drag the ①Slider to adjust.
Tap the ① Knob twice to open Color Picker. Drag the ②Slider to adjust color.
When finished, return to the canvas with ①✓ button.
Finished.