Note how the custom brush (a small circle) renders poorly (solid black lines and circle) This is because PHP is drawing that circle in the place of every single pixel in a standard brush.

To space out the brush to something more reasonable, you must combine the custom brush with a custom style.

Unlike using just a style, when using a custom brush and style the actual values of the the style array is irrlevant. Values greater than zero will cause the custom brush to be drawn while a value of zero will not.