_halfBlur(targetIn,targetOut,lodIn,lodOut,sigmaRadians,direction,poleAxis){const renderer=this._renderer;const blurMaterial=this._blurMaterial;if(direction!=='latitudinal'&&direction!=='longitudinal'){console.error('blur direction must be either latitudinal or longitudinal!');}// Number of standard deviations at which to cut off the discrete approximation.
const STANDARD_DEVIATIONS=3;const blurMesh=new _three_core_js__WEBPACK_IMPORTED_MODULE_0__.Mesh(this._lodPlanes[lodOut],blurMaterial);const blurUniforms=blurMaterial.uniforms;const pixels=this._sizeLods[lodIn]-1;const radiansPerPixel=isFinite(sigmaRadians)?Math.PI/(2*pixels):2*Math.PI/(2*MAX_SAMPLES-1);const sigmaPixels=sigmaRadians/radiansPerPixel;const samples=isFinite(sigmaRadians)?1+Math.floor(STANDARD_DEVIATIONS*sigmaPixels):MAX_SAMPLES;if(samples>MAX_SAMPLES){console.warn(`sigmaRadians, ${sigmaRadians}, is too large and will clip, as it requested ${samples} samples when the maximum is set to ${MAX_SAMPLES}`);}const weights=[];let sum=0;for(let i=0;i<MAX_SAMPLES;++i){const x=i/sigmaPixels;const weight=Math.exp(-x*x/2);weights.push(weight);if(i===0){sum+=weight;}else if(i<samples){sum+=2*weight;}}for(let i=0;i<weights.length;i++){weights[i]=weights[i]/sum;}blurUniforms['envMap'].value=targetIn.texture;blurUniforms['samples'].value=samples;blurUniforms['weights'].value=weights;blurUniforms['latitudinal'].value=direction==='latitudinal';if(poleAxis){blurUniforms['poleAxis'].value=poleAxis;}const{_lodMax}=this;blurUniforms['dTheta'].value=radiansPerPixel;blurUniforms['mipInt'].value=_lodMax-lodIn;const outputSize=this._sizeLods[lodOut];const x=3*outputSize*(lodOut>_lodMax-LOD_MIN?lodOut-_lodMax+LOD_MIN:0);const y=4*(this._cubeSize-outputSize);_setViewport(targetOut,x,y,3*outputSize,2*outputSize);renderer.setRenderTarget(targetOut);renderer.render(blurMesh,_flatCamera);}
This is a two-pass Gaussian blur for a cubemap. Normally this is done
vertically and horizontally, but this breaks down on a cube. Here we apply
the blur latitudinally (around the poles), and then longitudinally (towards
the poles) to approximate the orthogonally-separable blur. It is least
accurate at the poles, but still does a decent job.

@param {WebGLRenderTarget} cubeUVRenderTarget
@param {number} lodIn
@param {number} lodOut
@param {number} sigma
@param {Vector3} [poleAxis]