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                                                                    Exhibit 5.1

                                  July 25, 2000


                                                  Direct Dial:  (214) 740-8416
                                             e-mail: kjamison@lockeliddell.com


3dfx Interactive, Inc.
4435 Fortran Drive
San Jose, CA 95134

     Re: Registration Statement on Form S-8

Ladies and Gentlemen:

     We have examined the Registration Statement on Form S-8 filed by you with
the Securities Exchange Commission on July 25, 2000 (the "Registration
Statement"), in connection with the registration under the Securities Act of
1933, as amended, of 815,355 shares of your Common Stock (the "Shares"). As your
counsel in connection with this transaction, we have examined the proceedings
taken and are familiar with the proceedings proposed to be taken by you in
connection with the sales and issuance of the Shares.

     It is our opinion that upon conclusion of the proceedings being taken or
contemplated by us, as your counsel, to be taken prior to the issuance of the
Shares, and upon completion of the proceedings being taken in order to permit
such transactions to be carried out in accordance with the securities laws of
the various states where required, the Shares, when issued and sold in the
manner described in the Registration Statement, will be legally and validly
issued, fully paid and non-assessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement, and further consent to the use of our name wherever appearing in the
Registration Statement and any amendment thereto.

                            Very truly yours,

                            LOCKE LIDDELL & SAPP LLP



                            By: /s/ Kent Jamison
                                ----------------
                                Kent Jamison