Attached are a modified version of Bored's 3dfx scaling patch and corresponding test builds of DOSBox 0.74/SVN+3dfx scaling patch. Included with the test builds are SDL.dll, SDL_net.dll and dosbox.conf; there are no other files which these builds depend upon. Also, the following dosbox.conf settings should not be changed: fullscreen, fullresolution, windowresolution, output, aspect, scaler, and voodoo; the remaining settings may be changed. The two test builds consist of one which scales 2x in 3dfx mode while the other scales to 3x. Therefore, if your 3dfx DOS game runs at 640x480, then the 2x scaler will scale the game to 1280x960; the 3x scaler to 1920x1440. If your monitor has a native resolution of 1280x1024, then you can run the 2x scaler but not the 3x scaler because it will expand beyond the boundaries of your screen.
Modifications to Bored's patch include: centering the window instead of anchoring at the screen corner, reverted code to integer scaling instead of fractional scaling, removed automatic detection of resolution in sdl_main, a couple of edits to code, and removed lines which did not impact function. This version should run all 3dfx DOS games. This patch was only tested against EF2000, so once other 3dfx titles are tested, then a fractional scaler could be reintroduced into the code.
EF2000 fully works with Bored's patch, however, there is a graphical anomaly which does not affect gameplay. When zooming in to the instrument displays, then the surrounding background has an overlapping texture which is a mirror of the instruments. I know the source of this issue, it is the glVertex2f function which handles the 2d HUD display. When all is scaled but this HUD display, then the anomaly disappears; even the smallest degree of scaling causes this anomaly. I was unable to fix this issue at the level of the opengl function. Also, the fullscreen function will not preserve the aspect ratio of a game. This issue may also be caused by expanding the 2d HUD display. However, the quality and speed of the scaling is very high. As Bored indicated, this 3dfx-based scaling is without loss of quality in contrast to conventional scaling techniques based upon pixel placement.