To enable Double brush click “Use double brush” at the TEXTURE section, click on the double brush preview and select second brush from the Brushes panel
You can choose 2 types of double brush:
1)Mask enabled – second brush is the mask for the current brush:
Invert checkbox inverting mask alpha
GPU acceleration not working with the masked double brush
2)Mask disabled – second brush drawing with the current brush
Sometimes may be needed to synchronize some brushes parameters: for example, size random controller, angle and etc. you can enable Synchronization for this parameters:
This example shows how it works: first brush angle and size gets from the second brush parameters (in this example size with a random controller) But color, for example, is separate (to make color different you can use gradient or H/S/B sliders)
Size connect checkbox is connecting size change for 1st and 2nd brushes