This tool works on images, layers and vector layers, and requires the user to plot a series of nodes, perhaps around a motif, through which it will draw a smooth line.

Creating a brush outline

1. Activate a spot layer or an image and select the combined spline tool from the tools window or press S on the keyboard.
2. Draw the desired shape by clicking a series of points and then double click to end your spline. The shape will be painted automatically once you have double clicked using whichever brush is selected in the Brushes Palette.
   
   

Creating a filled shape

Repeat Steps 1 and 2 above but ensure that when you double click at the end of your shape you hold down the ⌘ (command key) key on the keyboard. The shape will be filled with solid colour automatically once you have double clicked. 

Creating a selection

Repeat Steps 1 and 2 above but ensure that when you double click at the end of your shape you hold down ⌥ (option) and ⌘ (command) keys on the keyboard. The shape will become a selection automatically once you have double clicked. 

Creating a vector shape

1. Activate a vector layer and select the combined spline tool from the Tools Palette or press S on the keyboard.
2. Draw the desired shape by clicking a series of points and then double click to end your spline. The shape will form a vector automatically once you have double clicked. 
   

Undoing the spline curve

Incorrect points along the line can be deleted while you are creating them by pressing ‘B’ on the keyboard to erase the points and move backwards one at a time.

Completing the spline curve

Double click at the point where you want the curve to finish and the spline will be completed. Alternatively, if you position your cursor exactly over the point where you started the line, you will notice that the software automatically tries to curve the final point itself, rather than leaving a straight section at the start and end. In this case, just click once and both ends will be joined together smoothly.