Q factor and resonance in resonant filter

Hi.
I need to calculate from scratch the coefficients for a resonant filter, and I'm no DSP guru...

googling around, I found the following formulae - which work fine, indeed:
a1 = -2r cos(2πfT)
a2 = r*r
b0 = g*(1-a2)/2
b1 = 0
b2 = -b0
with f being the center frequency, g the gain, r the resonance and T = 1/sr
(actually, in the filtergraph~ doc the a's and b's are swapped, but most on-line resources name the coefficients like this)

anyway. I'd love to be able to express the resonance in terms of Q factor, just like in reson~ or filtergraph~ ...

can anyone enlighten me on this subject, or point me towards some on-line resource???

thank you!
aa