Compute axis only once; take i==0 out of loop to remove conditional;

src/extras/PMREMGenerator.js

@@ -611,29 +611,28 @@ ${_getEncodings()}
 #define ENVMAP_TYPE_CUBE_UV
 #include <cube_uv_reflection_fragment>
 
-vec3 getSample(float theta) {
-	vec3 axis = latitudinal ? poleAxis : cross(poleAxis, vOutputDirection);
-	if (all(equal(axis, vec3(0.0))))
-		xis = cross(vec3(0.0, 1.0, 0.0), vOutputDirection);
-	axis = normalize(axis);
+vec3 getSample(float theta, vec3 axis) {
 	float cosTheta = cos(theta);
 	// Rodrigues' axis-angle rotation
-	vec3 sampleDirection = vOutputDirection * cosTheta 
-		+ cross(axis, vOutputDirection) * sin(theta) 
+	vec3 sampleDirection = vOutputDirection * cosTheta
+		+ cross(axis, vOutputDirection) * sin(theta)
 		+ axis * dot(axis, vOutputDirection) * (1.0 - cosTheta);
 	return bilinearCubeUV(envMap, sampleDirection, mipInt);
 }
 
 void main() {
+	vec3 axis = latitudinal ? poleAxis : cross(poleAxis, vOutputDirection);
+	if (all(equal(axis, vec3(0.0))))
+		axis = cross(vec3(0.0, 1.0, 0.0), vOutputDirection);
+	axis = normalize(axis);
 	gl_FragColor = vec4(0.0);
-	for (int i = 0; i < n; i++) {
+	gl_FragColor.rgb += weights[0] * getSample(0.0, axis);
+	for (int i = 1; i < n; i++) {
 		if (i >= samples)
 			break;
 		float theta = dTheta * float(i);
-		gl_FragColor.rgb += weights[i] * getSample(-1.0 * theta);
-		if(i == 0)
-			continue;
-		gl_FragColor.rgb += weights[i] * getSample(theta);
+		gl_FragColor.rgb += weights[i] * getSample(-1.0 * theta, axis);
+		gl_FragColor.rgb += weights[i] * getSample(theta, axis);
 	}
 	gl_FragColor = linearToOutputTexel(gl_FragColor);
 }