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stencil shadows ...

Started by Majestik666 Dec 5, 2002 at 7:46 PM 12 replies 500+ views

Original Post

Dec 5, 2002 at 7:46 PM

i''m currently implementing stencil shadows in my engine and i''m confronted to a performance problem, i spend most of my time rotating the normal of each face to check if it''s facing or not the light. is there a trick to improve this part of the code ? thanks

Gorg

Dec 5, 2002 at 8:38 PM

Bring the light position into object space instead of all your normals into worldspace.

Majestik666

Author

Majestik666

Dec 6, 2002 at 2:36 AM

thx for the help ...

well now ...
my shadows do not show up with a 2 pass rendering
(ambiant then illuminated).
is there an easy way to get a shot of
the current stencil buffer ?

thx

Dynaguy

Dec 6, 2002 at 6:46 AM

Are you using additive blending? Using SRCBLEND_ONE and DESTBLEND_ONE, each lightpass will slowly fade out the previous shadows. Use stencilpass always, stencilref 0x00, stencilfunc equal, for each light pass, so it only renders light where there is no shadow.

Majestik666

Author

Majestik666

Dec 6, 2002 at 8:27 AM

that''s what i''m doing

but i have a problem and don''t really know how to get rid of it...
in fact all my objects are modeled in Maya, and
i when i export the mesh, i also export a edge file
containing all the need edge informations
(vertex indices, and normal for each face),
but i thin my problem now is that my
vertices are not in the right order
all the time ...

how can i know or reorder my vertices
to make my shadow volume to render correctly to
the stencil buffer?

thx

Majestik666

Author

Majestik666

Dec 6, 2002 at 10:14 AM

i''ve put a shot online if anyone care to look at

http://perso.wanadoo.fr/majestik666/cube.jpg

thanks!

Dynaguy

Dec 6, 2002 at 12:34 PM

That screenshot is very unclear I''m afraid. It doesn''t seem the shadow caps are wrong cos you''d really notice with huge black tri''s going into infinity. So it''s probably not the winding order. Doubt Maya would screw up with something that trivial and important anyway. You could easily generate your own edge information to test though.

Majestik666

Author

Majestik666

Dec 6, 2002 at 9:01 PM

in fact after a lot of tries, i achieve a strange result,
depending on the camera position,
the shadow can display correctly or not...
here are two shots of the cube from different angles

wrong render :
http://perso.wanadoo.fr/majestik666/cube2.jpg

correct render :
http://perso.wanadoo.fr/majestik666/cube3.jpg

wrong render with wireframe :
http://perso.wanadoo.fr/majestik666/cube4.jpg
http://perso.wanadoo.fr/majestik666/cube4_w.jpg

the gray quads are rendered into the stencil buffer
and the whites segments are the normal to the
shadow volume quads

if it can helps ...

thx

Majestik666

Author

Majestik666

Dec 6, 2002 at 11:23 PM

sorry again

i found a Huge mistake in my shadow volume rendering code ...

now the shadow display mostly correctly ..
but i still have a problem
i put some shots online,
front shadow volume faces :
http://perso.wanadoo.fr/majestik666/volume_front.jpg
back shadow volume faces :
http://perso.wanadoo.fr/majestik666/volume_back.jpg

and the result :
http://perso.wanadoo.fr/majestik666/volume_final.jpg

as you can see there''s a little problem still with
my shadow volume generation, any idea ?

thx

Majestik666

Author

Majestik666

Dec 6, 2002 at 11:23 PM

sorry again

Majestik666

Author

Majestik666

Dec 7, 2002 at 3:51 AM

me, again and again

i found where the leak was, in fact
some of my edges are wrong outside of Maya...
which is very strange, cause i check the order of the
vertices from the faces list (which i use to render the
faces of the objects...)
i have to invert a few edges and the shadow is correct ...

does anyone have a simple edge creation code
to make them by myself instead of exporting them from maya ?

thx

Dynaguy

Dec 7, 2002 at 5:03 AM

For each face add all 3 edges through a function. This function checks if it''s already in the edgelist. If it doesn''t exist, add it to the first face of your edge structure. If it exists, my method ignores it, so you can have stuff like planes casting shadows. If it exists in opposite winding order, add it to the second face of the edge structure.

Majestik666

Author

Majestik666

Dec 8, 2002 at 2:34 AM

thanks for all your help guys !
i rewrote my maya exporter with a custom edge export thing
and it works perfectly ...

what are the main optimisations things i could try for the
stencil shadows ?
i tried the GL_EXT_STENCIL_TWO_SIDE extension, but
it''s not hardware on my board (Ge2 GTS) so .. around 0.01 fps
emulated

any other idea ?

thanks again!

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