Does this four variable quadratic condition describe a convex condition?

Question

Is following four variable parametrized quadratic condition $$f(a,b,c,d)=\big((c+d)r-{(a+b)}\big)^2+(r-ab)<\gamma$$ along with conditions $$0<c,d<1<a,b<r$$ convex at any fixed $r,\gamma>1$?