occt/src/Shaders/Display.fs

//! Input image.
uniform sampler2D uInputTexture;

//! Output pixel color.
out vec4 OutColor;

void main (void)
{
  vec4 aColor = texelFetch (uInputTexture, ivec2 (gl_FragCoord.xy), 0);

  // apply gamma correction (we use gamma = 2)
  OutColor = vec4 (sqrt (aColor.rgb), aColor.a);
}