Babylon.js/src/Shaders/vrDistortionCorrection.fragment.fx

// Samplers
varying vec2 vUV;
uniform sampler2D textureSampler;
uniform vec2 LensCenter;
uniform vec2 Scale;
uniform vec2 ScaleIn;
uniform vec4 HmdWarpParam;

vec2 HmdWarp(vec2 in01) {

	vec2 theta = (in01 - LensCenter) * ScaleIn; // Scales to [-1, 1]
	float rSq = theta.x * theta.x + theta.y * theta.y;
	vec2 rvector = theta * (HmdWarpParam.x + HmdWarpParam.y * rSq + HmdWarpParam.z * rSq * rSq + HmdWarpParam.w * rSq * rSq * rSq);
	return LensCenter + Scale * rvector;
}

void main(void)
{
	vec2 tc = HmdWarp(vUV);
	if (tc.x <0.0 || tc.x>1.0 || tc.y<0.0 || tc.y>1.0)
		gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
	else{
		gl_FragColor = vec4(texture2D(textureSampler, tc).rgb, 1.0);
	}
}