desaturation_shader_fs.glsl

#version 330 core
in vec2 uv;
uniform sampler2D sampler;
uniform float desaturationFactor;
out vec4 fragColor;
void main()
{
  vec3 color = texture2D( sampler , uv ).rgb;
  vec3 gray = vec3( dot( color , vec3( 0.2126 , 0.7152 , 0.0722 ) ) );
  fragColor = vec4( mix( color , gray , desaturationFactor ) , 1.0 );
}