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

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4 – A Fake Sphere in GLSL

GLSL Hacker - GLSL program to draw a fake sphere

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);
    gl_FragColor = bkg_color;

2 thoughts on “Circle, Disc and Fake Sphere in GLSL (Shader Library)”

  1. Nathan

    You can anti-alias the fake sphere’s edges by modifying the alpha channel with a smoothstep function. The one used in the Disc demo should do the trick, just adjust the values so it won’t be so thick.

  2. JeGX Post Author

    Thanks Nathan. I quickly ported the fake sphere demo without thinking to the antialiasing and as you said, the smoothstep function can help to antialiase.

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