C++ shader question - rendering

Question

Suppose I have some geometrical data and I wish to render it in wireframe mode. Obviously, this can be done using the API (for example, by setting some appropriate mode like D3DFILL_WIREFRAME in DirectX).
But I was interested if that is possible to achieve using vertex / geometry / pixel shaders (combined, probably).
Does someone have a sample of that?
Thank you.

Answer 1

Perhaps something like http://wn.com/DirectX_C++__Geometry_with_Wireframe_Effect ?
Try this: http://cgg-journal.com/2008-2/06/index.html -- code at the bottom
// ------------------ Vertex Shader --------------------------------
#version 120
#extension GL_EXT_gpu_shader4 : enable
void main(void)
{
gl_Position = ftransform();
}
// ------------------ Geometry Shader --------------------------------
#version 120
#extension GL_EXT_gpu_shader4 : enable
uniform vec2 WIN_SCALE;
noperspective varying vec3 dist;
void main(void)
{
vec2 p0 = WIN_SCALE * gl_PositionIn[0].xy/gl_PositionIn[0].w;
vec2 p1 = WIN_SCALE * gl_PositionIn[1].xy/gl_PositionIn[1].w;
vec2 p2 = WIN_SCALE * gl_PositionIn[2].xy/gl_PositionIn[2].w;
vec2 v0 = p2-p1;
vec2 v1 = p2-p0;
vec2 v2 = p1-p0;
float area = abs(v1.x*v2.y - v1.y * v2.x);
dist = vec3(area/length(v0),0,0);
gl_Position = gl_PositionIn[0];
EmitVertex();
dist = vec3(0,area/length(v1),0);
gl_Position = gl_PositionIn[1];
EmitVertex();
dist = vec3(0,0,area/length(v2));
gl_Position = gl_PositionIn[2];
EmitVertex();
EndPrimitive();
}
// ------------------ Fragment Shader --------------------------------
#version 120
#extension GL_EXT_gpu_shader4 : enable
noperspective varying vec3 dist;
const vec4 WIRE_COL = vec4(1.0,0.0,0.0,1);
const vec4 FILL_COL = vec4(1,1,1,1);
void main(void)
{
float d = min(dist[0],min(dist[1],dist[2]));
float I = exp2(-2*d*d);
gl_FragColor = I*WIRE_COL + (1.0 - I)*FILL_COL;
}