mipmapping should usually increase performance.
generating your own textures to be used at the smaller resolutions should look better than the ones from gluBuildMipmaps(…).
though of course this is time consuming esp if the artist has to paint them.
perhaps its best to rescale them with say gluScaleImage(…) + then check to see if theres any improvements u can make
Couldn’t you just use a program like photoshop to rescale the image? Halfing it each time using bicubic and you could probable just use the batch/action to do it.
On the performance note I definately notice a performance increase when using mipmaps.
MasterDark: if you rescaled the image in photoshop you’d need to store it on the HDD or somewhere, which would increase the space required for whatever program you are creating.
gluBuild2DMipMaps() uses gluScaleImage() internally to do at least some of the work.
If you want to see a method of generating your own mipmaps I believe there is one somewhere in the Quake 1 engine source code.