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;
}