Overriding ONLY Alpha value

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BOCCARA Michael (MICHAEL.BOCCARA++at++siege.aerospatiale.fr)
Wed, 12 Feb 1997 12:45:29 +0100

      Good morning Performers (from a french point of vue),

     I want to "ghostify" a part of my scene, ie I want to make it
     semi-transparent by applying a non-1 alpha value.
     For that I use a DRAW pre&post callback function.
     The only way I see is to create a new material with an alpha < 1.0f, to apply
     it, and to override the PFSTATE_FRONTMTL.
     But I don't want to loose the material colors of the child geodes.

     My question is :
     How (or is it possible) to override only the alpha value of the child
     geometry of a given node ?

     NB : all my subsequent geometry is (for the moment) non-textured, backface
     culled (no PFSTATE_BACKMTL)

     Here is a code sample, overriding the PFSTATE_FRONTMTL state mode

     int
     preApplyAlpha(pfTraverser *, void* data)
     (
       float alpha = *((float*) data);
       pfMaterial *mtl_alpha = new(pfGetSharedArena()) pfMaterial;
       mtl_alpha->setAlpha(alpha);
       mtl->apply();
       pfOverride(PFSTATE_FRONTMTL, PF_ON);
       delete mtl_alpha;
       return PFTRAV_CONT;
     )

     int
     preApplyAlpha(pfTraverser *, void*)
     (
      pfOverride(PFSTATE_FRONTMTL, PF_OFF);
      return PFTRAV_CONT;
     )

     I am using Performer 2.0.1, IRIX 5.3, on an Onyx RE2 or an High Impact.

     Thanks to the good soul who will help me,

     Mike

     Michaël Boccara ! Aerospatiale
     Virtual Simulation engineer ! Common Research
     email : ! Center - DCR/IK
     michael.boccara(a)siege.aerospatiale.fr ! 12 rue Pasteur
     Tel : (+33) (0)1 46 97 32 40 ! 92150 Suresnes
     Fax : (+33) (0)1 46 97 32 59 ! FRANCE

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