ragmentShader.replace(
                        'void main() {',
                        /* glsl */ `
                        uniform sampler2D thicknessMap;
                        uniform float thicknessDistortion;
                        uniform float thicknessAmbient;
                        uniform float thicknessAttenuation;
                        uniform float thicknessPower;
                        uniform float thicknessScale;

                        void RE_Direct_Scattering(IncidentLight directL