umituzun84 wrote:
> Hi Paul;
>
> Watch the video. It can tell you much of dot and cross product :)
>
> http://video.google.com/videosearch?q=cross+product&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&ei=LE4dSreZCpLt_AbS4OGxDQ&sa=X&oi=video_result_group&resnum=4&ct=title#
>
> (http://video.google.com/videosearch?q=cross+product&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&ei=LE4dSreZCpLt_AbS4OGxDQ&sa=X&oi=video_result_group&resnum=4&ct=title#)
>
> Regards.
>
> 2009/5/27 Paul Griffiths < ()>
>
> >
> > Kim C Bale wrote:
> >
> > > I presume this line:
> > >
> > > n = (pos1 -pos0) ^ (pos2 - pos1);
> > >
> > > is a cross product of two vectors. i.e. the normal, also known as the
> > > vector perpendicular to the two vectors that define the plane.
> > >
> > > In which case you would want to use the glsl function cross(vec3,vec3)
> > > as on the reference sheet I sent previously.
> > >
> > > You should have a read about the geometry math being used here. Blindy
> > > copying code without understanding it is a good way to shoot yourself in
> > > the foot later on.
> > >
> > >
> > > Kim.
> > >
> > >
> > > -----Original Message-----
> > > From:
> > >
> >
> >
> > > [mailto:] On Behalf Of Paul
> > > Griffiths
> > > Sent: 27 May 2009 13:40
> > > To:
> > >
> >
> >
> >
> > > Subject: Re: vertex shader help: compare position against
> > > plane
> > >
> > > ok, i got the world position with:
> > >
> > >
> > > Code:
> > > mat4 ToWorldMatrix= osg_ViewMatrixInverse* gl_ModelViewMatrix;
> > > vec3 worldPos = ToWorldMatrix * gl_Vertex;
> > >
> > >
> > >
> > >
> > > now i need to check which side of the plane the worldPos is.
> > > I googled and found some code for this but its not for glsl, ive came up
> > > with this but i get errors.
> > >
> > > the code is:
> > >
> > >
> > > Code:
> > > vec3 n;
> > > float d;
> > >
> > > n = (pos1 -pos0) ^ (pos2 - pos1);
> > > d = -n * pos0;
> > >
> > > inside = 1.0;
> > >
> > > if (dot(n, gl_Position) + w)
> > > {
> > > inside = 0.0;
> > > }
> > >
> > >
> > >
> > >
> > > the errors i get are:
> > >
> > >
> > > Code:
> > > VERTEX glCompileShader "" FAILED
> > > VERTEX Shader "" infolog:
> > > 0(46) : error C1021: operands to "^" must be integral
> > >
> > > glLinkProgram "eroded" FAILED
> > > Program "eroded" infolog:
> > > Vertex info
> > > -----------
> > > 0(46) : error C1021: operands to "^" must be integral
> > >
> > > Warning: detected OpenGL error 'invalid operation' after
> > > RenderBin::draw(,)
> > >
> > >
> > >
> > >
> > > so i tried
> > >
> > >
> > > Code:
> > > vec3 n;
> > > float w;
> > >
> > > int p0 = (pos1 -pos0);
> > > int p1 = (pos2 - pos1);
> > > n = p0 ^ p1;
> > > w = -n * pos0;
> > > inside = 1.0;
> > >
> > > if (dot(n, worldPos) + w)
> > > {
> > > inside = 0.0;
> > > }
> > >
> > >
> > >
> > > but it alway returns inside = 0.0;
> > >
> > > any ideas?
> > >
> > > ------------------
> > > Read this topic online here:
> > > http://forum.openscenegraph.org/viewtopic.php?p=13031#13031
> > > (http://forum.openscenegraph.org/viewtopic.php?p=13031#13031)
> > >
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > osg-users mailing list
> > >
> > >
> >
> >
> >
> > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or
> > > (http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or)
> > > g
> > >
> >
> >
> > > *****************************************************************************************
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> > > (http://www.hull.ac.uk/legal/email_disclaimer.html)
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> > >
> > >
> >
> >
> > > ------------------
> > > Post generated by Mail2Forum
> > >
> >
> >
> > Thanks kim. am new to this 3d math stuff.
> >
> > ------------------
> > Read this topic online here:
> >
> > http://forum.openscenegraph.org/viewtopic.php?p=13051#13051
> > (http://forum.openscenegraph.org/viewtopic.php?p=13051#13051)
> >
> >
> >
> >
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> >
>
>
>
> --
> Ümit Uzun
>
> ------------------
> Post generated by Mail2Forum
Thaks umituzun84, for the link. Ill have a watch when im home and not on mobile
broadband.
-----------------------------------------------------------------------------
Ive got my code working. But its clipping to a vertex level when I need it down
to the fragment level.
Is it possible to get the fragment world position in some way?
heres my code so far:
Vertex shader:
Code:
varying float lightIntensity;
varying vec3 Position;
uniform vec3 LightPosition;
uniform float Scale;
varying float inside;
uniform mat4 osg_ViewMatrixInverse;
varying vec3 pos0;
varying vec3 pos1;
varying vec3 pos2;
void main(void) {
vec4 pos = gl_ModelViewMatrix * gl_Vertex;
Position = vec3(gl_Vertex) * Scale;
vec3 tnorm = normalize(gl_NormalMatrix * gl_Normal);
float dotval = max(dot(normalize(LightPosition - vec3(pos)), tnorm),
0.0);
lightIntensity = dotval * 1.5;
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
pos0.x = 0.4;
pos0.y = 0.0;
pos0.z = 0.0;
pos1.x = 0.4;
pos1.y = 1.0;
pos1.z = 0.0;
pos2.x = 0.4;
pos2.y = 0.0;
pos2.z = 1.0;
mat4 ToWorldMatrix = osg_ViewMatrixInverse * gl_ModelViewMatrix;
vec3 worldPos = ToWorldMatrix * gl_Vertex;
vec3 n;
float d;
n = cross((pos1 -pos0),(pos2 - pos1));
d = -n * pos0;
inside = 1.0;
if (dot(n, worldPos) + d > 0.0)
{
inside = 0.0;
}
}
Fragment Shader:
Code:
varying float lightIntensity;
varying vec3 Position;
varying float inside;
void main (void)
{
if (inside) discard;
vec3 color;
color.r = 1.0;
color.g = 0.0;
color.b = 0.0;
color *= lightIntensity;
color = clamp(color, 0.0, 1.0);
gl_FragColor = vec4 (color, 1.0);
}
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=13058#13058
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