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
>
>
>
>
>
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Thanks kim. am new to this 3d math stuff.
------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=13051#13051
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