(Shader Library) Fish Eye, Dome and Barrel Distortion GLSL Post Processing Filters



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3 – Dome Distortion Shader



This shader is based on the following links:



Dome projection requires a fish eye projector lens, which necessarily distorts the image. A fisheye lens is needed for the projector to display across the nearly 180° of the dome. This necessarily introduces a distortion of the graphics that is being displayed through it. The trick is to then “pre-distort” the graphics in the opposite direction before sending it on to the projector.

The following GLSL program (which is not a post processing filter because it directly acts on the 3D object) shows the pre-distort effect:



Vertex shader:

#version 120
varying vec4 Vertex_UV;
uniform mat4 gxl3d_ModelViewMatrix;
uniform mat4 gxl3d_ProjectionMatrix;

uniform int do_distorsion;

const float PI = 3.1415926535;

void main()
{
  vec4 P = gxl3d_ModelViewMatrix * gl_Vertex;
  if (do_distorsion == 1)
  {  
    float rxy = length(P.xy);
    if (rxy > 0)
    {
      float phi = atan(rxy, -P.z);
      float lens_radius = phi * 180.0 / PI * 2.0;
      P.xy *= (lens_radius / rxy);
    }
  }
  gl_Position = gxl3d_ProjectionMatrix * P;
  Vertex_UV = gl_MultiTexCoord0 * 10.0;
}



Fragment shader:

#version 120
void main()
{
  gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}

(GLSL Shader Library) Fish Eye Post Processing Filter, Dome Distortion, barrel distortion
Dome distortion enabled

(GLSL Shader Library) Fish Eye Post Processing Filter, Dome Distortion, barrel distortion
Dome distortion disabled




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