The brushes are kinda funky and weak in the GIMP. For the simple shape brushes, like circle and square, you can select a scale factor and it'll be properly scaled (it's an option separate from the initial size). I figure the whole brushes thing will be dealt with eventually, as far as having some base shapes (circle, line, N-sided regular polygon) and parameters for each like photoshop, and complex raster brushes being separate. I don't think the GIMP even has much to specify the hardness of a brush at the moment other than "fully hard" and "fully soft".

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