Circle, Disc and Fake Sphere in GLSL (Shader Library)

Article index:

• 1 – Simple Circle in GLSL
• 2 – A better Circle in GLSL
• 3 – A Disc in GLSL
• 4 – A Fake Sphere in GLSL

4 – A Fake Sphere in GLSL

The fake sphere is a simple port of this GeeXLab demo.

Vertex shader:

#version 120    
void main()
{
  gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;		
  gl_TexCoord[0] = gl_MultiTexCoord0;
}

Fragment shader:

#version 120    
uniform sampler2D tex0;
uniform vec4 bkg_color;
uniform float time;
void main (void)
{
  vec2 p = -1.0 + 2.0 * gl_TexCoord[0].xy;
  float r = sqrt(dot(p,p));
  if (r < 1.0)
  {
    vec2 uv;
    float f = (1.0-sqrt(1.0-r))/(r);
    uv.x = p.x*f + time;
    uv.y = p.y*f + time;
    gl_FragColor = texture2D(tex0,uv);
  }
  else
  {
    gl_FragColor = bkg_color;
  }
}