Hi,

I created a shader in order to clip an object with a user defined clipping plane.

First I use the "standard OpenGL clipping", but this way restricted me too much because I just want to clip specific objects and not the whole halfspace.
So I decided to try it with GLSL.

Here my Vertex Shader:

varying float xpos;
varying float ypos;
varying float zpos;
varying vec3 normalVec;

varying float entfernung;

void main(void)
{
xpos = gl_Vertex.x;
ypos = gl_Vertex.y;
zpos = gl_Vertex.z;

normalVec = normalize (gl_NormalMatrix * gl_Normal);

gl_FrontColor = gl_Color;
gl_Position = ftransform();
}

And here my Fragment Shader: (clipping plane: Z = 10)

varying float xpos;
varying float ypos;
varying float zpos;

varying vec3 normalVec;

int enabled = 1;
bool invert = false;

float intensity;

float entfernung;

void main(void)
{
if(enabled == 1)
{

entfernung = zpos-10;

vec4 farbe = vec4(gl_Color);

if (!invert)
{
if (entfernung >= 0.0)
discard;
}
else
{
if (entfernung <= 0.0)
discard;
}
intensity = dot (vec3 (gl_LightSource[0].position), normalVec);
gl_FragColor = farbe * intensity;
}
else
{
gl_FragColor = gl_Color;
}
}

The result is that the object is clipped by the plane z=10. That's ok.
But taking a look at the "clipping side", I can look through the modell.
Means I have no back side.
(Is there no possibility to add an image?)

Can anybody help me? Or have anybody another idea how I can clip an modell?
I read something about a way to clip is to use a projected 2DTexture with a 2x1 texture, where 1 pixel alpha = 255 and the other pixel alpha = 0.
But I don't really understand it resp. don't know how to make it in this way.
Searching the www is until now not very helpful.

Thanks for help!!!