Pa, prvo nacrtas oblik kakav hoces da ima brush, pa ga selektujes; ili selektujes sliku/deo slike. Za ostre ivice podesi feather na 0px. Zatim ides Edit->Define brush preset. Daj mu ime, OK, i to je to.
Edit:
Evo, gledam, pise u Helpu...
The only place you can find Success before Work is in the dictionary.
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If you want to shoot, then - shoot; don't talk!
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One shot - one hit...