View Full Version : Weird Specular
08-25-2002, 02:30 AM
Hi, im implementing a per-pixel lighting solution in my litle engine.
im using half-vector to aproximate specular reflections, but it looks strange, my specular highlights have a spherical aspect (instead of something elipsoidal i think).
is this correct ?
08-25-2002, 03:04 AM
pictures of what you have and what you want?
08-25-2002, 03:10 AM
hum, my spec highlights look something like, imagine a flat plane, now imagine a specular highlight that's totaly spherical (literally).
i've opened 3dmax3 meanwhile and been playing around with lights and the specular should be elipsoidal (or something like that, my english sucks ass a bit).
any thoughts, suggestions are welcome http://www.opengl.org/discussion_boards/ubb/wink.gif
08-25-2002, 03:14 AM
well, show what you do mathematical/codewise.. something went wrong, we have to find what, and without code thats really uhm.. difficult? http://www.opengl.org/discussion_boards/ubb/biggrin.gif
08-25-2002, 03:24 AM
im computing light and half vector in a vertex shader, then light and half vector's are normalized with a normalization cube map.
the math is something like:
light vector= light pos- vertex pos
half vector= eye pos-vertex pos
half vector+= ligth vector
then stuff is transformed into tangent space and saved in respective output registers.
then in pixel shader, i compute:
normalized light vector (dot3) normal map
normalized half vector (dot3) normal map
aproximate spec to ^16
and sum results (no decal & ambient)
any thoughts ?
tks again btw http://www.opengl.org/discussion_boards/ubb/wink.gif
08-25-2002, 03:32 AM
hm sounds okay.. if you tesselate the geometry to near_to_perpixel triangles, does it get bether? normally, you would need to _calculate_ the halfangle perpixel, means normalizing point_to_light and point_to_eye perpixel, and then summing them up (and normalize again http://www.opengl.org/discussion_boards/ubb/biggrin.gif god bless approx_normalize for pixelshaders.. http://www.opengl.org/discussion_boards/ubb/biggrin.gif)
if you sum them up before, and do the normalization, the direction of the halfangle gets wrong => wrong shading occurs..
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