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.