Packed attributes less efficient ?

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CHRISTOPHE.C.D.DELEPINE++at++TTS.thomson.fr
13 Mar 1998 10:12:14 +0000

In order to improve rendering performance, i have experimented geosets with
packed attributes, but unfortunately the rendering time has increased (~20%)
compared with the same geosets without packed attributes. A bit strange
since it is supposed to decrease OpenGL function call overhead...

my packed vertex looks like:

short n[4];
float t[2];
float v[3];

the color is not included because it is constant per geoset.

here is the geoset initialisation code for packed attributes:

        pfGSetDrawMode(gs->gset, PFGS_PACKED_ATTRS, PF_ON);
        pfGSetAttr(gs->gset, PFGS_PACKED_ATTRS, PFGS_PA_C4UBN3ST2FV3F, gs->ntv, NULL);
        pfGSetAttr(gs->gset, PFGS_COORD3, PFGS_PER_VERTEX, NULL, NULL);
        pfGSetAttr(gs->gset, PFGS_NORMAL3, PFGS_PER_VERTEX, NULL, NULL);
        pfGSetAttr(gs->gset, PFGS_TEXCOORD2, PFGS_PER_VERTEX, NULL, NULL);

and the one for non packed attributes:

        pfGSetAttr(gs->gset, PFGS_COORD3, PFGS_PER_VERTEX, gs->point, NULL);
        pfGSetAttr(gs->gset, PFGS_NORMAL3, PFGS_PER_VERTEX, gs->normal, NULL);
        pfGSetAttr(gs->gset, PFGS_TEXCOORD2, PFGS_PER_VERTEX, gs->uv, NULL);

Any idea that could explain the loss of performance ?
Would it be faster to use directly OpenGL (glDrawArrayEXT) with attributes stored
in separate arrays (which is not possible to specify with Performer) ?

machine: Onyx2 + performer 2.2

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email: christophe.delepine++at++tts.thomson.fr

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